sELF_control

sELF control

Category

Reverse

Description

I found a program to read the flag but it seems to be broken... Could you help me patching patching two bytes to make it functional ?

Host : chall0.heroctf.fr
Port : 2048

Format : Hero{flag}
Author : SoEasY

Files

• READFLAG.bin

Write up

The title of the challenge is containing a clue : "ELF". We can check the ELF header then (see wikipedia here, a we find that :

• The architecture is not correct (IA-64 instead of amd64)
• The entry point is 0x10A1 instead of 0x10A0 (see _start and start)

Solution

$ nc chall0.heroctf.fr 2048
██╗  ██╗███████╗██████╗  ██████╗  ██████╗████████╗███████╗
██║  ██║██╔════╝██╔══██╗██╔═══██╗██╔════╝╚══██╔══╝██╔════╝
███████║█████╗  ██████╔╝██║   ██║██║        ██║   █████╗  
██╔══██║██╔══╝  ██╔══██╗██║   ██║██║        ██║   ██╔══╝  
██║  ██║███████╗██║  ██║╚██████╔╝╚██████╗   ██║   ██║     
╚═╝  ╚═╝╚══════╝╚═╝  ╚═╝ ╚═════╝  ╚═════╝   ╚═╝   ╚═╝     
================ sELF control (by SoEasY) ================


Position of the byte to patch in hex (example: 03) : 12
Value to put at this offset in hex (example: 14) : 3e

Position of the byte to patch in hex (example: 1C) : 18
Value to put at this offset in hex (example: 03) : A0

[+] Execution : 
Hero{W0w_s0_y0u_4r3_4n_ELF_h34d3r_M4sT3r???}

Flag

Hero{W0w_s0_y0u_4r3_4n_ELF_h34d3r_M4sT3r???}