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Darkwebmessageboard

dark

Category:

OSINT , Crypto , Web

That's a lot of categories boy.

Difficulty:

It was pretty difficult

Writeup:

DISCLAIMER : This is going to be super LONG.....

This chall looked interesting because of its three different categories. So I completed the three parts one by one.

First Phase: OSINT

The url http://darkboard-01.pwn.beer:5001 gave a page dark2 a cool one with a password form. So I viewed the source and found the string :

| Dark Web Message Board | DEVELOPED BY K1tsCr3w | Open source at Kits-AB

which was commented out. Open Source gave a hint to github. So I searched in github for the user Kits-AB and got the source for the website. https://github.com/kits-ab/the-dark-message-board. Checking the directories, robots.txt caught my eye. It had an entry /boards/*. Opening http://darkboard-01.pwn.beer:5001/boards/1 gave a message board which contained lot of messages. The one which was of importance was :

rW+fOddzrtdP7ufLj9KTQa9W8T9JhEj7a2AITFA4a2UbeEAtV/ocxB/t4ikLCMsThUXXWz+UFnyXzgLgD9RM+2toOvWRiJPBM2ASjobT+bLLi31F2M3jPfqYK1L9NCSMcmpVGs+OZZhzJmTbfHLdUcDzDwdZcjKcGbwEGlL6Z7+CbHD7RvoJk7Ft3wvFZ7PWIUHPneVAsAglOalJQCyWKtkksy9oUdDfCL9yvLDV4H4HoXGfQwUbLJL4Qx4hXHh3fHDoplTqYdkhi/5E4l6HO0Qh/jmkNLuwUyhcZVnFMet1vK07ePAuu7kkMe6iZ8FNtmluFlLnrlQXrE74Z2vHbQ==

It was encrypted with something. Getting back to git repo, the tests dir had a test_crypto.py (this file was of super importance). Since it was OSINT the repo had 3 commits. So I looked the commit history which had this fishy commit which was deleted. dark3 So i viewed it and it had a PRIVATE_KEY (which was to be used later) and a description:

removed the production key, luckily it was encrypted with a password …

…from some file that reminds me of the song 'here i am something like a hurricane'

The song in the description was Rock_You_Like_a_Hurricane , so with this I concluded that somehow rockyou.txt was involved in the chall. And this ends our OSINT phase.

Second Phase: Crypto

Now comes the file test_crypto.py. Understanding the file, the script carries out random generation of private keys on top of a password and a PADDING... (Boy oh Boy that much Security).So this was the script in a nutshell, with this we needed to find a password from rockyou.txt to decrypt the text obtained from /boards/1 . So i modified the test_crypto.py to accomplish this. Here's my modified decryption function.

with open("rockyou.txt", errors='replace') as f:
    r = f.readlines()
    p_list = [i.strip() for i in r]
for l in p_list:
    try:
        private_key =      
        serialization.load_pem_private_key(
                    PEM_PRIVATE_KEY,
                    password=bytes(l, 'utf-8'),
                    backend=default_backend() )
                    
        plaintext = private_key.decrypt(
    base64.b64decode(ENCRYPTED_MESSAGE.encode('utf-8')),DEFAULT_PADDING)
        print(plaintext)
    except:
        continue

I looped thorugh all the pwds from rockyou to get a hit and replaced the PRIVATE_KEY with the one given in github deleted commit and waited for the decrypted text to appear. The heavy load nearly crashed my box. The decrypted text was a URL for our next phase.

Bank url: http://bankofsweden-01.pwn.beer

This marked the end for our Crypto Phase.

Third Phase: Web

Now the last and the longest phase. Opening the URL obtained got me nowhere. So the chall desription had this :

You will find a URL. If it says https://XXXXXXXXX/, change it to http://XXXXXXXXX:5000/

So our modified URL changed to http://bankofsweden-01.pwn.beer:5000

It directed us to the BANK website which the chall had in its description. It had a Login and Registration form. I registered with some creds but for some reason the account did'nt seem to activate. So while registering, I captured the request with Burp-Suite. It had an is_active param. Setting it to true did the trick to activate our account. dark4 Logging in gave us a Greeting msg (Nice site) dark5 Exploring the site, it had two features IMPORT and EXPORT. I first used the export feature dark6 When I clicked the export btn It tried to open a file which wasn't present in the dir. So It was a bit suspicious. So I called my frnd BURP again and captured the req. The param account had LFI so I used it to my advantage. dark7 Hahah I got /etc/passwd. Now the real part came. looking for the flag..... It took some time to find the dir and the flag file. Using /proc/self/environ I looked through the env variables and found this:

PWD=/home/bos/ctf

This was the last lead which I found and it took me a while to figure out that the webapp was FLASKED...(based on flask). So I looked tried tha app.py inside ctf/

/home/bos/ctf/app.py dark8

and yeaaa....It worked and the flag was right there.

sctf{h4ck3r5_60nn4_h4ck_4nd_b4nk3r5_60nn4_cr4ck}

That was the longest chall I ever solved. Hats off the my team mates: nullpxl mrT4ntr4 for helping me with this chall.

Hope u like it. Team Dc1ph3R.

The full script to the crypto part: darkcrypto.py