From 937ac1fe069a4dc8471dff205f553d82e724015b Mon Sep 17 00:00:00 2001
From: Ned Deily <nad@python.org>
Date: Sun, 11 Mar 2018 14:29:05 -0400
Subject: [PATCH] [3.5] bpo-32981: Fix catastrophic backtracking vulns
 (GH-5955) (#6034)

* 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)
---
 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/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 000000000000..9ebabb44f91e
--- /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.