[2.7] bpo-32981: Fix catastrophic backtracking vulns (GH-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 <tim.peters@gmail.com>
Co-authored-by: Christian Heimes <christian@python.org>.
(cherry picked from commit 0e6c8ee2358a2e23117501826c008842acb835ac)
diff --git a/Lib/test/test_poplib.py b/Lib/test/test_poplib.py
index 23d6887..d214375 100644
--- a/Lib/test/test_poplib.py
+++ b/Lib/test/test_poplib.py
@@ -211,6 +211,16 @@
def test_rpop(self):
self.assertOK(self.client.rpop('foo'))
+ 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 = ('+OK 116 bytes',
['From: postmaster@python.org', 'Content-Type: text/plain',