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>
Co-authored-by: Jamie Davis <davisjam@vt.edu>
(cherry picked from commit 0e6c8ee2358a2e23117501826c008842acb835ac)

1 files changed, 1 insertions, 0 deletions

diff --git a/Misc/ACKS b/Misc/ACKS
index 4c0b0e5720..d598520e93 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