247CTF - My Magic Bytes

Posted on In Views: Disqus: Word count in article: 175 Reading time ≈ 1 mins.

Socket challenge requiring automation to solve 500 arithmetic problems programmatically. Use Python with pwntools to interface with the remote service and automate the solution.

Key Considerations

  • Library: pwntools for socket communication
  • Custom delimiter: Uses \r\n instead of standard \n
  • Approach: Parse math expressions dynamically and compute answers

Solution

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#!/usr/bin/env python3
import pwn

HOST = "7a3875d00fa5d462.247ctf.com"
PORT = 50337

pwn.context.log_level = "info"
pwn.tube.newline = b"\r\n"


def solve_challenge():
    conn = None
    try:
        conn = pwn.remote(HOST, PORT)

        for i in range(500):
            conn.recvuntil(b"answer to ")
            question_line = conn.recvline().decode().strip()
            expression = question_line.replace("?", "")
            result = int(eval(expression))
            conn.sendline(str(result).encode())
            pwn.log.info(f"Progress: [{i + 1}/500] Solved: {expression} = {result}")

        pwn.log.success("500 problems solved! Waiting for flag...")
        conn.interactive()

    except Exception as e:
        pwn.log.error(f"An error occurred: {e}")

    finally:
        if conn:
            pwn.log.info("Connection closed.")
            conn.close()


if __name__ == "__main__":
    solve_challenge()

Execution Output

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❯ python tcp_auto.py
[+] Opening connection to 7a3875d00fa5d462.247ctf.com on port 50337: Done
...
[*] Progress: [499/500] Solved: 221 + 474 = 695
[*] Progress: [500/500] Solved: 4 + 449 = 453
[+] 500 problems solved! Waiting for flag...
[*] Switching to interactive mode
247CTF{flag_here}