From 34e25a97709a05f7c804036dd1e16afda6bdfa33 Mon Sep 17 00:00:00 2001 From: Victor Stinner Date: Thu, 30 Jan 2020 16:13:03 +0100 Subject: [PATCH 1/2] bpo-39503: Fix urllib basic auth regex The AbstractBasicAuthHandler class of the urllib.request module uses an inefficient regular expression which can be exploited by an attacker to cause a denial of service. Fix the regex to prevent the catastrophic backtracking. Vulnerability reported by Matt Schwager. --- Lib/urllib2.py | 2 +- Misc/NEWS.d/next/Security/2020-01-30-16-15-29.bpo-39503.B299Yq.rst | 4 ++++ 2 files changed, 5 insertions(+), 1 deletion(-) create mode 100644 Misc/NEWS.d/next/Security/2020-01-30-16-15-29.bpo-39503.B299Yq.rst --- /dev/null +++ b/Misc/NEWS.d/next/Security/2020-01-30-16-15-29.bpo-39503.B299Yq.rst @@ -0,0 +1,4 @@ +CVE-2020-8492: The :class:`~urllib.request.AbstractBasicAuthHandler` class of the +:mod:`urllib.request` module uses an inefficient regular expression which can +be exploited by an attacker to cause a denial of service. Fix the regex to +prevent the catastrophic backtracking. Vulnerability reported by Matt Schwager. --- a/Lib/urllib2.py +++ b/Lib/urllib2.py @@ -856,7 +856,7 @@ class AbstractBasicAuthHandler: # allow for double- and single-quoted realm values # (single quotes are a violation of the RFC, but appear in the wild) - rx = re.compile('(?:.*,)*[ \t]*([^ \t]+)[ \t]+' + rx = re.compile('(?:[^,]*,)*[ \t]*([^ \t]+)[ \t]+' 'realm=(["\']?)([^"\']*)\\2', re.I) # XXX could pre-emptively send auth info already accepted (RFC 2617,