PIcoCTF 2018 – Binary Exploitation - buffer overflow0

PIcoCTF 2018 – Binary Exploitation - buffer overflow0

Objective:

Let's start off simple, can you overflow the right buffer in this program [1]  to get the flag? You can also find it in /problems/buffer-overflow-0_1_316c391426b9319fbdfb523ee15b37db on the shell server. Source [2] .

Hints:

(1)    How can you trigger the flag to print? (2) 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:

  I started by CDing over to the problem folder

Ls shows us a flag file(Which we can’t open) the program and the c code

The title tells us this is about a buffer over flow

Running the program we get this

./vuln

This program takes 1 argument.

Ok let’s give it an argument

./vuln 1

Thanks! Received: 1

Lets try just throwing a bunch values at it

./vuln 11111111111111111111111111111111111

picoCTF{ov3rfl0ws_ar3nt_that_bad_3598a894}

that was super simple but expected since it was the first flag in binary exploitation