diff options
| -rw-r--r-- | dev-requirements.txt | 1 | ||||
| -rw-r--r-- | paramiko/auth_handler.py | 36 | ||||
| -rw-r--r-- | paramiko/transport.py | 24 | ||||
| -rw-r--r-- | sites/www/changelog.rst | 17 | ||||
| -rw-r--r-- | tests/test_transport.py | 76 |
5 files changed, 143 insertions, 11 deletions
diff --git a/dev-requirements.txt b/dev-requirements.txt index 7f2ab0b9..8814627f 100644 --- a/dev-requirements.txt +++ b/dev-requirements.txt @@ -6,6 +6,7 @@ pytest>=3.2,<3.3 pytest-relaxed==1.1.4 # pytest-xdist for test dir watching and the inv guard task pytest-xdist>=1.22,<2.0 +mock==2.0.0 # Linting! flake8==2.4.0 # Coverage! diff --git a/paramiko/auth_handler.py b/paramiko/auth_handler.py index 3f0456e5..26605a16 100644 --- a/paramiko/auth_handler.py +++ b/paramiko/auth_handler.py @@ -705,17 +705,39 @@ Error Message: {} self.auth_event.set() return - _handler_table = { + # TODO: do the same to the other tables, in Transport. + # TODO 3.0: MAY make sense to make these tables into actual + # classes/instances that can be fed a mode bool or whatever. Or, + # alternately (both?) make the message types small classes or enums that + # embed this info within themselves (which could also then tidy up the + # current 'integer -> human readable short string' stuff in common.py). + # TODO: if we do that, also expose 'em publicly. + + # Messages which should be handled _by_ servers (sent by clients) + _server_handler_table = { MSG_SERVICE_REQUEST: _parse_service_request, - MSG_SERVICE_ACCEPT: _parse_service_accept, MSG_USERAUTH_REQUEST: _parse_userauth_request, + MSG_USERAUTH_INFO_RESPONSE: _parse_userauth_info_response, + } + + # Messages which should be handled _by_ clients (sent by servers) + _client_handler_table = { + MSG_SERVICE_ACCEPT: _parse_service_accept, MSG_USERAUTH_SUCCESS: _parse_userauth_success, MSG_USERAUTH_FAILURE: _parse_userauth_failure, MSG_USERAUTH_BANNER: _parse_userauth_banner, MSG_USERAUTH_INFO_REQUEST: _parse_userauth_info_request, - MSG_USERAUTH_INFO_RESPONSE: _parse_userauth_info_response, } + # NOTE: prior to the fix for #1283, this was a static dict instead of a + # property. Should be backwards compatible in most/all cases. + @property + def _handler_table(self): + if self.transport.server_mode: + return self._server_handler_table + else: + return self._client_handler_table + class GssapiWithMicAuthHandler(object): """A specialized Auth handler for gssapi-with-mic @@ -811,9 +833,15 @@ class GssapiWithMicAuthHandler(object): self._restore_delegate_auth_handler() return self._delegate._parse_userauth_request(m) - _handler_table = { + __handler_table = { MSG_SERVICE_REQUEST: _parse_service_request, MSG_USERAUTH_REQUEST: _parse_userauth_request, MSG_USERAUTH_GSSAPI_TOKEN: _parse_userauth_gssapi_token, MSG_USERAUTH_GSSAPI_MIC: _parse_userauth_gssapi_mic, } + + @property + def _handler_table(self): + # TODO: determine if we can cut this up like we did for the primary + # AuthHandler class. + return self.__handler_table diff --git a/paramiko/transport.py b/paramiko/transport.py index aa3b8dcc..410ff273 100644 --- a/paramiko/transport.py +++ b/paramiko/transport.py @@ -82,6 +82,8 @@ from paramiko.common import ( DEFAULT_WINDOW_SIZE, DEFAULT_MAX_PACKET_SIZE, HIGHEST_USERAUTH_MESSAGE_ID, + MSG_UNIMPLEMENTED, + MSG_NAMES, ) from paramiko.compress import ZlibCompressor, ZlibDecompressor from paramiko.dsskey import DSSKey @@ -2035,12 +2037,22 @@ class Transport(threading.Thread, ClosingContextManager): if len(self._expected_packet) > 0: continue else: - err = "Oops, unhandled type {:d}".format(ptype) - self._log(WARNING, err) - msg = Message() - msg.add_byte(cMSG_UNIMPLEMENTED) - msg.add_int(m.seqno) - self._send_message(msg) + # Respond with "I don't implement this particular + # message type" message (unless the message type was + # itself literally MSG_UNIMPLEMENTED, in which case, we + # just shut up to avoid causing a useless loop). + name = MSG_NAMES[ptype] + self._log( + WARNING, + "Oops, unhandled type {} ({!r})".format( + ptype, name + ), + ) + if ptype != MSG_UNIMPLEMENTED: + msg = Message() + msg.add_byte(cMSG_UNIMPLEMENTED) + msg.add_int(m.seqno) + self._send_message(msg) self.packetizer.complete_handshake() except SSHException as e: self._log(ERROR, "Exception: " + str(e)) diff --git a/sites/www/changelog.rst b/sites/www/changelog.rst index 67a8bb00..be488de6 100644 --- a/sites/www/changelog.rst +++ b/sites/www/changelog.rst @@ -2,6 +2,23 @@ Changelog ========= +- :bug:`-` Modify protocol message handling such that ``Transport`` does not + respond to ``MSG_UNIMPLEMENTED`` with its own ``MSG_UNIMPLEMENTED`` message. + This behavior probably didn't cause any outright errors, but it doesn't seem + to conform to the RFCs and could cause (non-infinite) feedback loops in some + scenarios (usually those involving Paramiko on both ends). +- :bug:`1283 (1.17+)` Fix exploit (CVE pending) in Paramiko's server mode + (**not** client mode) where hostile clients could trick the server into + thinking they were authenticated without actually submitting valid + authentication. + + Specifically, steps have been taken to start separating client and server + related message types in the message handling tables within ``Transport`` and + ``AuthHandler``; this work is not complete but enough has been performed to + close off this particular exploit (which was the only obvious such exploit + for this particular channel). + + Thanks to Daniel Hoffman for the detailed report. - :support:`1292 backported` Backport changes from :issue:`979` (added in Paramiko 2.3) to Paramiko 2.0-2.2, using duck-typing to preserve backwards compatibility. This allows these older versions to use newer Cryptography diff --git a/tests/test_transport.py b/tests/test_transport.py index 13fb302e..2b8ee3bc 100644 --- a/tests/test_transport.py +++ b/tests/test_transport.py @@ -30,6 +30,7 @@ import threading import random from hashlib import sha1 import unittest +from mock import Mock from paramiko import ( Transport, @@ -41,19 +42,24 @@ from paramiko import ( ChannelException, Packetizer, Channel, + AuthHandler, ) from paramiko import AUTH_FAILED, AUTH_SUCCESSFUL from paramiko import OPEN_SUCCEEDED, OPEN_FAILED_ADMINISTRATIVELY_PROHIBITED from paramiko.common import ( MSG_KEXINIT, cMSG_CHANNEL_WINDOW_ADJUST, + cMSG_UNIMPLEMENTED, MIN_PACKET_SIZE, MIN_WINDOW_SIZE, MAX_WINDOW_SIZE, DEFAULT_WINDOW_SIZE, DEFAULT_MAX_PACKET_SIZE, + MSG_NAMES, + MSG_UNIMPLEMENTED, + MSG_USERAUTH_SUCCESS, ) -from paramiko.py3compat import bytes +from paramiko.py3compat import bytes, byte_chr from paramiko.message import Message from .util import needs_builtin, _support, slow @@ -1027,3 +1033,71 @@ class TransportTest(unittest.TestCase): assert "forwarding request denied" in str(e) else: assert False, "Did not raise SSHException!" + + def _send_unimplemented(self, server_is_sender): + self.setup_test_server() + sender, recipient = self.tc, self.ts + if server_is_sender: + sender, recipient = self.ts, self.tc + recipient._send_message = Mock() + msg = Message() + msg.add_byte(cMSG_UNIMPLEMENTED) + sender._send_message(msg) + # TODO: I hate this but I literally don't see a good way to know when + # the recipient has received the sender's message (there are no + # existing threading events in play that work for this), esp in this + # case where we don't WANT a response (as otherwise we could + # potentially try blocking on the sender's receipt of a reply...maybe). + time.sleep(0.1) + assert not recipient._send_message.called + + def test_server_does_not_respond_to_MSG_UNIMPLEMENTED(self): + self._send_unimplemented(server_is_sender=False) + + def test_client_does_not_respond_to_MSG_UNIMPLEMENTED(self): + self._send_unimplemented(server_is_sender=True) + + def _send_client_message(self, message_type): + self.setup_test_server(connect_kwargs={}) + self.ts._send_message = Mock() + # NOTE: this isn't 100% realistic (most of these message types would + # have actual other fields in 'em) but it suffices to test the level of + # message dispatch we're interested in here. + msg = Message() + # TODO: really not liking the whole cMSG_XXX vs MSG_XXX duality right + # now, esp since the former is almost always just byte_chr(the + # latter)...but since that's the case... + msg.add_byte(byte_chr(message_type)) + self.tc._send_message(msg) + # No good way to actually wait for server action (see above tests re: + # MSG_UNIMPLEMENTED). Grump. + time.sleep(0.1) + + def _expect_unimplemented(self): + # Ensure MSG_UNIMPLEMENTED was sent (implies it hit end of loop instead + # of truly handling the given message). + # NOTE: When bug present, this will actually be the first thing that + # fails (since in many cases actual message handling doesn't involve + # sending a message back right away). + assert self.ts._send_message.call_count == 1 + reply = self.ts._send_message.call_args[0][0] + reply.rewind() # Because it's pre-send, not post-receive + assert reply.get_byte() == cMSG_UNIMPLEMENTED + + def test_server_transports_reject_client_message_types(self): + # TODO: handle Transport's own tables too, not just its inner auth + # handler's table. See TODOs in auth_handler.py + for message_type in AuthHandler._client_handler_table: + self._send_client_message(message_type) + self._expect_unimplemented() + # Reset for rest of loop + self.tearDown() + self.setUp() + + def test_server_rejects_client_MSG_USERAUTH_SUCCESS(self): + self._send_client_message(MSG_USERAUTH_SUCCESS) + # Sanity checks + assert not self.ts.authenticated + assert not self.ts.auth_handler.authenticated + # Real fix's behavior + self._expect_unimplemented() |