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python3-doc.35772
CVE-2023-40217-avoid-ssl-pre-close.patch
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File CVE-2023-40217-avoid-ssl-pre-close.patch of Package python3-doc.35772
From f0c1e55dfd28970196768a6997a6dc0eab0f5259 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?=C5=81ukasz=20Langa?= <lukasz@langa.pl> Date: Tue, 22 Aug 2023 17:39:17 +0200 Subject: [PATCH] gh-108310: Fix CVE-2023-40217: Check for & avoid the ssl pre-close flaw MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Instances of `ssl.SSLSocket` were vulnerable to a bypass of the TLS handshake and included protections (like certificate verification) and treating sent unencrypted data as if it were post-handshake TLS encrypted data. The vulnerability is caused when a socket is connected, data is sent by the malicious peer and stored in a buffer, and then the malicious peer closes the socket within a small timing window before the other peers’ TLS handshake can begin. After this sequence of events the closed socket will not immediately attempt a TLS handshake due to not being connected but will also allow the buffered data to be read as if a successful TLS handshake had occurred. Co-Authored-By: Gregory P. Smith [Google LLC] <greg@krypto.org> --- Lib/ssl.py | 35 + Lib/test/test_ssl.py | 214 ++++++++++ Misc/NEWS.d/next/Security/2023-08-22-17-39-12.gh-issue-108310.fVM3sg.rst | 7 3 files changed, 253 insertions(+), 3 deletions(-) create mode 100644 Misc/NEWS.d/next/Security/2023-08-22-17-39-12.gh-issue-108310.fVM3sg.rst --- a/Lib/ssl.py +++ b/Lib/ssl.py @@ -543,6 +543,8 @@ class SSLSocket(socket): "in client mode") if self._context.check_hostname and not server_hostname: raise ValueError("check_hostname requires server_hostname") + self._closed = False + self._sslobj = None self.server_side = server_side self.server_hostname = server_hostname self.do_handshake_on_connect = do_handshake_on_connect @@ -553,7 +555,7 @@ class SSLSocket(socket): type=sock.type, proto=sock.proto, fileno=sock.fileno()) - self.settimeout(sock.gettimeout()) + sock_timeout = sock.gettimeout() sock.detach() elif fileno is not None: socket.__init__(self, fileno=fileno) @@ -567,11 +569,38 @@ class SSLSocket(socket): if e.errno != errno.ENOTCONN: raise connected = False + blocking = self.gettimeout() == 0 + self.setblocking(False) + try: + # We are not connected so this is not supposed to block, but + # testing revealed otherwise on macOS and Windows so we do + # the non-blocking dance regardless. Our raise when any data + # is found means consuming the data is harmless. + notconn_pre_handshake_data = self.recv(1) + except OSError as e: + # EINVAL occurs for recv(1) on non-connected on unix sockets. + if e.errno not in (errno.ENOTCONN, errno.EINVAL): + raise + notconn_pre_handshake_data = b'' + self.setblocking(blocking) + if notconn_pre_handshake_data: + # This prevents pending data sent to the socket before it was + # closed from escaping to the caller who could otherwise + # presume it came through a successful TLS connection. + reason = "Closed before TLS handshake with data in recv buffer." + notconn_pre_handshake_data_error = SSLError(e.errno, reason) + # Add the SSLError attributes that _ssl.c always adds. + notconn_pre_handshake_data_error.reason = reason + notconn_pre_handshake_data_error.library = None + try: + self.close() + except OSError: + pass + raise notconn_pre_handshake_data_error else: connected = True - self._closed = False - self._sslobj = None + self.settimeout(sock_timeout) # Must come after setblocking() calls. self._connected = connected if connected: # create the SSL object --- a/Lib/test/test_ssl.py +++ b/Lib/test/test_ssl.py @@ -3,11 +3,14 @@ import sys import unittest from test import support +import re import socket import select +import struct import time import datetime import gc +import http.client import os import errno import pprint @@ -2917,6 +2920,217 @@ else: self.assertRaises(ValueError, s.write, b'hello') +def set_socket_so_linger_on_with_zero_timeout(sock): + sock.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER, struct.pack('ii', 1, 0)) + + +class TestPreHandshakeClose(unittest.TestCase): + """Verify behavior of close sockets with received data before to the handshake. + """ + + class SingleConnectionTestServerThread(threading.Thread): + + def __init__(self, *, name, call_after_accept): + self.call_after_accept = call_after_accept + self.received_data = b'' # set by .run() + self.wrap_error = None # set by .run() + self.listener = None # set by .start() + self.port = None # set by .start() + super().__init__(name=name) + + def __enter__(self): + self.start() + return self + + def __exit__(self, *args): + try: + if self.listener: + self.listener.close() + except OSError: + pass + self.join() + self.wrap_error = None # avoid dangling references + + def start(self): + self.ssl_ctx = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH) + self.ssl_ctx.verify_mode = ssl.CERT_REQUIRED + self.ssl_ctx.load_verify_locations(cafile=ONLYCERT) + self.ssl_ctx.load_cert_chain(certfile=ONLYCERT, keyfile=ONLYKEY) + self.listener = socket.socket() + self.port = support.bind_port(self.listener) + self.listener.settimeout(2.0) + self.listener.listen(1) + super().start() + + def run(self): + conn, address = self.listener.accept() + self.listener.close() + with conn: + if self.call_after_accept(conn): + return + try: + tls_socket = self.ssl_ctx.wrap_socket(conn, server_side=True) + except OSError as err: # ssl.SSLError inherits from OSError + self.wrap_error = err + else: + try: + self.received_data = tls_socket.recv(400) + except OSError: + pass # closed, protocol error, etc. + + def non_linux_skip_if_other_okay_error(self, err): + if sys.platform == "linux": + return # Expect the full test setup to always work on Linux. + if (isinstance(err, ConnectionResetError) or + (isinstance(err, OSError) and err.errno == errno.EINVAL) or + re.search('wrong.version.number', getattr(err, "reason", ""), re.I)): + # On Windows the TCP RST leads to a ConnectionResetError + # (ECONNRESET) which Linux doesn't appear to surface to userspace. + # If wrap_socket() winds up on the "if connected:" path and doing + # the actual wrapping... we get an SSLError from OpenSSL. Typically + # WRONG_VERSION_NUMBER. While appropriate, neither is the scenario + # we're specifically trying to test. The way this test is written + # is known to work on Linux. We'll skip it anywhere else that it + # does not present as doing so. + self.skipTest("Could not recreate conditions on %s: %s" % (sys.platform, err)) + # If maintaining this conditional winds up being a problem. + # just turn this into an unconditional skip anything but Linux. + # The important thing is that our CI has the logic covered. + + def test_preauth_data_to_tls_server(self): + server_accept_called = threading.Event() + ready_for_server_wrap_socket = threading.Event() + + def call_after_accept(unused): + server_accept_called.set() + if not ready_for_server_wrap_socket.wait(2.0): + raise RuntimeError("wrap_socket event never set, test may fail.") + return False # Tell the server thread to continue. + + server = self.SingleConnectionTestServerThread( + call_after_accept=call_after_accept, + name="preauth_data_to_tls_server") + server.__enter__() # starts it + self.addCleanup(server.__exit__) # ... & unittest.TestCase stops it. + + with socket.socket() as client: + client.connect(server.listener.getsockname()) + # This forces an immediate connection close via RST on .close(). + set_socket_so_linger_on_with_zero_timeout(client) + client.setblocking(False) + + server_accept_called.wait() + client.send(b"DELETE /data HTTP/1.0\r\n\r\n") + client.close() # RST + + ready_for_server_wrap_socket.set() + server.join() + wrap_error = server.wrap_error + self.assertEqual(b"", server.received_data) + self.assertIsInstance(wrap_error, OSError) # All platforms. + self.non_linux_skip_if_other_okay_error(wrap_error) + self.assertIsInstance(wrap_error, ssl.SSLError) + self.assertIn("before TLS handshake with data", wrap_error.args[1]) + self.assertIn("before TLS handshake with data", wrap_error.reason) + self.assertNotEqual(0, wrap_error.args[0]) + self.assertIsNone(wrap_error.library, msg="attr must exist") + + def test_preauth_data_to_tls_client(self): + client_can_continue_with_wrap_socket = threading.Event() + + def call_after_accept(conn_to_client): + # This forces an immediate connection close via RST on .close(). + set_socket_so_linger_on_with_zero_timeout(conn_to_client) + conn_to_client.send( + b"HTTP/1.0 307 Temporary Redirect\r\n" + b"Location: https://example.com/someone-elses-server\r\n" + b"\r\n") + conn_to_client.close() # RST + client_can_continue_with_wrap_socket.set() + return True # Tell the server to stop. + + server = self.SingleConnectionTestServerThread( + call_after_accept=call_after_accept, + name="preauth_data_to_tls_client") + server.__enter__() # starts it + self.addCleanup(server.__exit__) # ... & unittest.TestCase stops it. + + # Redundant; call_after_accept sets SO_LINGER on the accepted conn. + set_socket_so_linger_on_with_zero_timeout(server.listener) + + with socket.socket() as client: + client.connect(server.listener.getsockname()) + if not client_can_continue_with_wrap_socket.wait(2.0): + self.fail("test server took too long.") + ssl_ctx = ssl.create_default_context() + try: + tls_client = ssl_ctx.wrap_socket( + client, server_hostname="localhost") + except OSError as err: # SSLError inherits from OSError + wrap_error = err + received_data = b"" + else: + wrap_error = None + received_data = tls_client.recv(400) + tls_client.close() + + server.join() + self.assertEqual(b"", received_data) + self.assertIsInstance(wrap_error, OSError) # All platforms. + self.non_linux_skip_if_other_okay_error(wrap_error) + self.assertIsInstance(wrap_error, ssl.SSLError) + self.assertIn("before TLS handshake with data", wrap_error.args[1]) + self.assertIn("before TLS handshake with data", wrap_error.reason) + self.assertNotEqual(0, wrap_error.args[0]) + self.assertIsNone(wrap_error.library, msg="attr must exist") + + def test_https_client_non_tls_response_ignored(self): + + server_responding = threading.Event() + + class SynchronizedHTTPSConnection(http.client.HTTPSConnection): + def connect(self): + http.client.HTTPConnection.connect(self) + # Wait for our fault injection server to have done its thing. + if not server_responding.wait(1.0) and support.verbose: + sys.stdout.write("server_responding event never set.") + self.sock = self._context.wrap_socket( + self.sock, server_hostname=self.host) + + def call_after_accept(conn_to_client): + # This forces an immediate connection close via RST on .close(). + set_socket_so_linger_on_with_zero_timeout(conn_to_client) + conn_to_client.send( + b"HTTP/1.0 402 Payment Required\r\n" + b"\r\n") + conn_to_client.close() # RST + server_responding.set() + return True # Tell the server to stop. + + server = self.SingleConnectionTestServerThread( + call_after_accept=call_after_accept, + name="non_tls_http_RST_responder") + server.__enter__() # starts it + self.addCleanup(server.__exit__) # ... & unittest.TestCase stops it. + # Redundant; call_after_accept sets SO_LINGER on the accepted conn. + set_socket_so_linger_on_with_zero_timeout(server.listener) + + connection = SynchronizedHTTPSConnection( + "localhost", + port=server.port, + context=ssl.create_default_context(), + timeout=2.0, + ) + # There are lots of reasons this raises as desired, long before this + # test was added. Sending the request requires a successful TLS wrapped + # socket; that fails if the connection is broken. It may seem pointless + # to test this. It serves as an illustration of something that we never + # want to happen... properly not happening. + with self.assertRaises(OSError) as err_ctx: + connection.request("HEAD", "/test", headers={"Host": "localhost"}) + response = connection.getresponse() + + def test_main(verbose=False): if support.verbose: plats = { --- /dev/null +++ b/Misc/NEWS.d/next/Security/2023-08-22-17-39-12.gh-issue-108310.fVM3sg.rst @@ -0,0 +1,7 @@ +Fixed an issue where instances of :class:`ssl.SSLSocket` were vulnerable to +a bypass of the TLS handshake and included protections (like certificate +verification) and treating sent unencrypted data as if it were +post-handshake TLS encrypted data. Security issue reported as +`CVE-2023-40217 +<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-40217>`_ by +Aapo Oksman. Patch by Gregory P. Smith.
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