From 0e6c8ee2358a2e23117501826c008842acb835ac Mon Sep 17 00:00:00 2001 From: Jamie Davis Date: Sun, 4 Mar 2018 00:33:32 -0500 Subject: bpo-32981: Fix catastrophic backtracking vulns (#5955) * Prevent low-grade poplib REDOS (CVE-2018-1060) The regex to test a mail server's timestamp is susceptible to catastrophic backtracking on long evil responses from the server. Happily, the maximum length of malicious inputs is 2K thanks to a limit introduced in the fix for CVE-2013-1752. A 2KB evil response from the mail server would result in small slowdowns (milliseconds vs. microseconds) accumulated over many apop calls. This is a potential DOS vector via accumulated slowdowns. Replace it with a similar non-vulnerable regex. The new regex is RFC compliant. The old regex was non-compliant in edge cases. * Prevent difflib REDOS (CVE-2018-1061) The default regex for IS_LINE_JUNK is susceptible to catastrophic backtracking. This is a potential DOS vector. Replace it with an equivalent non-vulnerable regex. Also introduce unit and REDOS tests for difflib. Co-authored-by: Tim Peters Co-authored-by: Christian Heimes --- Lib/difflib.py | 2 +- Lib/poplib.py | 2 +- Lib/test/test_difflib.py | 22 +++++++++++++++++++++- Lib/test/test_poplib.py | 12 +++++++++++- Misc/ACKS | 1 + .../2018-03-02-10-24-52.bpo-32981.O_qDyj.rst | 4 ++++ 6 files changed, 39 insertions(+), 4 deletions(-) create mode 100644 Misc/NEWS.d/next/Security/2018-03-02-10-24-52.bpo-32981.O_qDyj.rst diff --git a/Lib/difflib.py b/Lib/difflib.py index 8296471..043a169 100644 --- a/Lib/difflib.py +++ b/Lib/difflib.py @@ -1083,7 +1083,7 @@ class Differ: import re -def IS_LINE_JUNK(line, pat=re.compile(r"\s*#?\s*$").match): +def IS_LINE_JUNK(line, pat=re.compile(r"\s*(?:#\s*)?$").match): r""" Return 1 for ignorable line: iff `line` is blank or contains a single '#'. diff --git a/Lib/poplib.py b/Lib/poplib.py index 6bcfa5c..d8a62c0 100644 --- a/Lib/poplib.py +++ b/Lib/poplib.py @@ -308,7 +308,7 @@ class POP3: return self._shortcmd('RPOP %s' % user) - timestamp = re.compile(br'\+OK.*(<[^>]+>)') + timestamp = re.compile(br'\+OK.[^<]*(<.*>)') def apop(self, user, password): """Authorisation diff --git a/Lib/test/test_difflib.py b/Lib/test/test_difflib.py index 156b523..aaefe6d 100644 --- a/Lib/test/test_difflib.py +++ b/Lib/test/test_difflib.py @@ -466,13 +466,33 @@ class TestBytes(unittest.TestCase): list(generator(*args)) self.assertEqual(msg, str(ctx.exception)) +class TestJunkAPIs(unittest.TestCase): + def test_is_line_junk_true(self): + for line in ['#', ' ', ' #', '# ', ' # ', '']: + self.assertTrue(difflib.IS_LINE_JUNK(line), repr(line)) + + def test_is_line_junk_false(self): + for line in ['##', ' ##', '## ', 'abc ', 'abc #', 'Mr. Moose is up!']: + self.assertFalse(difflib.IS_LINE_JUNK(line), repr(line)) + + def test_is_line_junk_REDOS(self): + evil_input = ('\t' * 1000000) + '##' + self.assertFalse(difflib.IS_LINE_JUNK(evil_input)) + + def test_is_character_junk_true(self): + for char in [' ', '\t']: + self.assertTrue(difflib.IS_CHARACTER_JUNK(char), repr(char)) + + def test_is_character_junk_false(self): + for char in ['a', '#', '\n', '\f', '\r', '\v']: + self.assertFalse(difflib.IS_CHARACTER_JUNK(char), repr(char)) def test_main(): difflib.HtmlDiff._default_prefix = 0 Doctests = doctest.DocTestSuite(difflib) run_unittest( TestWithAscii, TestAutojunk, TestSFpatches, TestSFbugs, - TestOutputFormat, TestBytes, Doctests) + TestOutputFormat, TestBytes, TestJunkAPIs, Doctests) if __name__ == '__main__': test_main() diff --git a/Lib/test/test_poplib.py b/Lib/test/test_poplib.py index fd0db79..bf568bd 100644 --- a/Lib/test/test_poplib.py +++ b/Lib/test/test_poplib.py @@ -308,9 +308,19 @@ class TestPOP3Class(TestCase): def test_rpop(self): self.assertOK(self.client.rpop('foo')) - def test_apop(self): + def test_apop_normal(self): self.assertOK(self.client.apop('foo', 'dummypassword')) + def test_apop_REDOS(self): + # Replace welcome with very long evil welcome. + # NB The upper bound on welcome length is currently 2048. + # At this length, evil input makes each apop call take + # on the order of milliseconds instead of microseconds. + evil_welcome = b'+OK' + (b'<' * 1000000) + with test_support.swap_attr(self.client, 'welcome', evil_welcome): + # The evil welcome is invalid, so apop should throw. + self.assertRaises(poplib.error_proto, self.client.apop, 'a', 'kb') + def test_top(self): expected = (b'+OK 116 bytes', [b'From: postmaster@python.org', b'Content-Type: text/plain', diff --git a/Misc/ACKS b/Misc/ACKS index e2addfc..d8179c8 100644 --- a/Misc/ACKS +++ b/Misc/ACKS @@ -356,6 +356,7 @@ Jonathan Dasteel Pierre-Yves David A. Jesse Jiryu Davis Jake Davis +Jamie (James C.) Davis Ratnadeep Debnath Merlijn van Deen John DeGood diff --git a/Misc/NEWS.d/next/Security/2018-03-02-10-24-52.bpo-32981.O_qDyj.rst b/Misc/NEWS.d/next/Security/2018-03-02-10-24-52.bpo-32981.O_qDyj.rst new file mode 100644 index 0000000..9ebabb4 --- /dev/null +++ b/Misc/NEWS.d/next/Security/2018-03-02-10-24-52.bpo-32981.O_qDyj.rst @@ -0,0 +1,4 @@ +Regexes in difflib and poplib were vulnerable to catastrophic backtracking. +These regexes formed potential DOS vectors (REDOS). They have been +refactored. This resolves CVE-2018-1060 and CVE-2018-1061. +Patch by Jamie Davis. -- cgit v0.12