8000 CVE-2021-4189 cherry-pick Fix 4134f154ae2f621f25c5d698cc0f1748035a1b88 · ActiveState/cpython@73bb207 · GitHub
[go: up one dir, main page]
Skip to content

Commit 73bb207

Browse files
rickpricegpshead
rickprice
and
gpshead
committed
CVE-2021-4189 cherry-pick Fix 4134f15
[3.6] bpo-43285 Make ftplib not trust the PASV response. (pythonGH-24838) (G… …H-24881) (pythonGH-24882) The IPv4 address value returned from the server in response to the PASV command should not be trusted. This prevents a malicious FTP server from using the response to probe IPv4 address and port combinations on the client network. Instead of using the returned address, we use the IP address we're already connected to. This is the strategy other ftp clients adopted, and matches the only strategy available for the modern IPv6 EPSV command where the server response must return a port number and nothing else. For the rare user who _wants_ this ugly behavior, set a `trust_server_pasv_ipv4_address` attribute on your `ftplib.FTP` instance to True.. (cherry picked from commit 0ab152c) Co-authored-by: Gregory P. Smith <greg@krypto.org> (cherry picked from commit 664d1d1)
1 parent 8627fbf commit 73bb207

File tree

4 files changed

+135
-5
lines changed

4 files changed

+135
-5
lines changed

‎Doc/whatsnew/2.7.rst

Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2777,6 +2777,15 @@ It has been replaced by the new ``make regen-all`` target.
27772777
27782778
.. _acks27:
27792779

2780+
Security fix for FTP
2781+
================================
2782+
2783+
A security fix alters the :class:`ftplib.FTP` behavior to not trust the
2784+
IPv4 address sent from the remote server when setting up a passive data
2785+
channel. We reuse the ftp server IP address instead. For unusual code
2786+
requiring the old behavior, set a ``trust_server_pasv_ipv4_address``
2787+
attribute on your FTP instance to ``True``. (See :issue:`43285`)
2788+
27802789
Acknowledgements
27812790
================
27822791

‎Lib/ftplib.py

Lines changed: 9 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -108,6 +108,9 @@ class FTP:
108108
file = None
109109
welcome = None
110110
passiveserver = 1
111+
encoding = "latin-1"
112+
# Disables https://bugs.python.org/issue43285 security if set to True.
113+
trust_server_pasv_ipv4_address = False
111114

112115
# Initialization method (called by class instantiation).
113116
# Initialize host to localhost, port to standard ftp port
@@ -310,8 +313,13 @@ def makeport(self):
310313
return sock
311314

312315
def makepasv(self):
316+
"""Internal: Does the PASV or EPSV handshake -> (address, port)"""
313317
if self.af == socket.AF_INET:
314-
host, port = parse227(self.sendcmd('PASV'))
318+
untrusted_host, port = parse227(self.sendcmd('PASV'))
319+
if self.trust_server_pasv_ipv4_address:
320+
host = untrusted_host
321+
else:
322+
host = self.sock.getpeername()[0]
315323
else:
316324
host, port = parse229(self.sendcmd('EPSV'), self.sock.getpeername())
317325
return host, port

‎Lib/test/test_ftplib.py

Lines changed: 109 additions & 4 deletions
9E88
Original file line numberDiff line numberDiff line change
@@ -67,6 +67,10 @@ def __init__(self, conn):
6767
self.rest = None
6868
self.next_retr_data = RETR_DATA
6969
self.push('220 welcome')
70+
# We use this as the string IPv4 address to direct the client
71+
# to in response to a PASV command. To test security behavior.
72+
# https://bugs.python.org/issue43285/.
73+
self.fake_pasv_server_ip = '252.253.254.255'
7074

7175
def collect_incoming_data(self, data):
7276
self.in_buffer.append(data)
@@ -109,13 +113,13 @@ def cmd_pasv(self, arg):
109113
sock.bind((self.socket.getsockname()[0], 0))
110114
sock.listen(5)
111115
sock.settimeout(10)
112-
ip, port = sock.getsockname()[:2]
113-
ip = ip.replace('.', ',')
114-
p1, p2 = divmod(port, 256)
116+
port = sock.getsockname()[1]
117+
ip = self.fake_pasv_server_ip
118+
ip = ip.replace('.', ','); p1 = port / 256; p2 = port % 256
115119
self.push('227 entering passive mode (%s,%d,%d)' %(ip, p1, p2))
116120
conn, addr = sock.accept()
117121
self.dtp = self.dtp_handler(conn, baseclass=self)
118-
122+
119123
def cmd_eprt(self, arg):
120124
af, ip, port = arg.split(arg[0])[1:-1]
121125
port = int(port)
@@ -577,6 +581,107 @@ def test_makepasv(self):
577581
# IPv4 is in use, just make sure send_epsv has not been used
578582
self.assertEqual(self.server.handler_instance.last_received_cmd, 'pasv')
579583

584+
def test_makepasv_issue43285_security_disabled(self):
585+
"""Test the opt-in to the old vulnerable behavior."""
586+
self.client.trust_server_pasv_ipv4_address = True
587+
bad_host, port = self.client.makepasv()
588+
self.assertEqual(
589+
bad_host, self.server.handler_instance.fake_pasv_server_ip)
590+
# Opening and closing a connection keeps the dummy server happy
591+
# instead of timing out on accept.
592+
socket.create_connection((self.client.sock.getpeername()[0], port),
593+
timeout=TIMEOUT).close()
594+
595+
def test_makepasv_issue43285_security_enabled_default(self):
596+
self.assertFalse(self.client.trust_server_pasv_ipv4_address)
597+
trusted_host, port = self.client.makepasv()
598+
self.assertNotEqual(
599+
trusted_host, self.server.handler_instance.fake_pasv_server_ip)
600+
# Opening and closing a connection keeps the dummy server happy
601+
# instead of timing out on accept.
602+
socket.create_connection((trusted_host, port), timeout=TIMEOUT).close()
603+
604+
def test_with_statement(self):
605+
self.client.quit()
606+
607+
def is_client_connected():
608+
if self.client.sock is None:
609+
return False
610+
try:
611+
self.client.sendcmd('noop')
612+
except (OSError, EOFError):
613+
return False
614+
return True
615+
616+
# base test
617+
with ftplib.FTP(timeout=TIMEOUT) as self.client:
618+
self.client.connect(self.server.host, self.server.port)
619+
self.client.sendcmd('noop')
620+
self.assertTrue(is_client_connected())
621+
self.assertEqual(self.server.handler_instance.last_received_cmd, 'quit')
622+
self.assertFalse(is_client_connected())
623+
624+
# QUIT sent inside the with block
625+
with ftplib.FTP(timeout=TIMEOUT) as self.client:
626+
self.client.connect(self.server.host, self.server.port)
627+
self.client.sendcmd('noop')
628+
self.client.quit()
629+
self.assertEqual(self.server.handler_instance.last_received_cmd, 'quit')
630+
self.assertFalse(is_client_connected())
631+
632+
# force a wrong response code to be sent on QUIT: error_perm
633+
# is expected and the connection is supposed to be closed
634+
try:
635+
with ftplib.FTP(timeout=TIMEOUT) as self.client:
636+
self.client.connect(self.server.host, self.server.port)
637+
self.client.sendcmd('noop')
638+
self.server.handler_instance.next_response = '550 error on quit'
639+
except ftplib.error_perm as err:
640+
self.assertEqual(str(err), '550 error on quit')
641+
else:
642+
self.fail('Exception not raised')
643+
# needed to give the threaded server some time to set the attribute
644+
# which otherwise would still be == 'noop'
645+
time.sleep(0.1)
646+
self.assertEqual(self.server.handler_instance.last_received_cmd, 'quit')
647+
self.assertFalse(is_client_connected())
648+
649+
def test_source_address(self):
650+
self.client.quit()
651+
port = support.find_unused_port()
652+
try:
653+
self.client.connect(self.server.host, self.server.port,
654+
source_address=(HOST, port))
655+
self.assertEqual(self.client.sock.getsockname()[1], port)
656+
self.client.quit()
657+
except OSError as e:
658+
if e.errno == errno.EADDRINUSE:
659+
self.skipTest("couldn't bind to port %d" % port)
660+
raise
661+
662+
def test_source_address_passive_connection(self):
663+
port = support.find_unused_port()
664+
self.client.source_address = (HOST, port)
665+
try:
666+
with self.client.transfercmd('list') as sock:
667+
self.assertEqual(sock.getsockname()[1], port)
668+
except OSError as e:
669+
if e.errno == errno.EADDRINUSE:
670+
self.skipTest("couldn't bind to port %d" % port)
671+
raise
672+
673+
def test_parse257(self):
674+
self.assertEqual(ftplib.parse257('257 "/foo/bar"'), '/foo/bar')
675+
self.assertEqual(ftplib.parse257('257 "/foo/bar" created'), '/foo/bar')
676+
self.assertEqual(ftplib.parse257('257 ""'), '')
677+
self.assertEqual(ftplib.parse257('257 "" created'), '')
678+
self.assertRaises(ftplib.error_reply, ftplib.parse257, '250 "/foo/bar"')
679+
# The 257 response is supposed to include the directory
680+
# name and in case it contains embedded double-quotes
681+
# they must be doubled (see RFC-959, chapter 7, appendix 2).
682+
self.assertEqual(ftplib.parse257('257 "/foo/b""ar"'), '/foo/b"ar')
683+
self.assertEqual(ftplib.parse257('257 "/foo/b""ar" created'), '/foo/b"ar')
684+
580685
def test_line_too_long(self):
581686
self.assertRaises(ftplib.Error, self.client.sendcmd,
582687
'x' * self.client.maxline * 2)

‎Misc/NEWS.d/next/Security/2021-03-13-03-48-14.bpo-43285.g-Hah3.rst

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,8 @@
1+
:mod:`ftplib` no longer trusts the IP address value returned from the server
2+
in response to the PASV command by default. This prevents a malicious FTP
3+
server from using the response to probe IPv4 address and port combinations
4+
on the client network.
5+
6+
Code that requires the former vulnerable behavior may set a
7+
``trust_server_pasv_ipv4_address`` attribute on their
8+
:class:`ftplib.FTP` instances to ``True`` to re-enable it.

0 commit comments

Comments
 (0)
0