From 29c669440dddba61d18e1b7fdd57180cae9e4ae3 Mon Sep 17 00:00:00 2001
From: Yeting Li <liyt@ios.ac.cn>
Date: Wed, 7 Apr 2021 19:27:41 +0800
Subject: [PATCH] bpo-43075: Fix ReDoS in urllib AbstractBasicAuthHandler
 (GH-24391)

Fix Regular Expression Denial of Service (ReDoS) vulnerability in
urllib.request.AbstractBasicAuthHandler. The ReDoS-vulnerable regex
has quadratic worst-case complexity and it allows cause a denial of
service when identifying crafted invalid RFCs. This ReDoS issue is on
the client side and needs remote attackers to control the HTTP server.
(cherry picked from commit 7215d1ae25525c92b026166f9d5cac85fb1defe1)

Co-authored-by: Yeting Li <liyt@ios.ac.cn>
---
 Lib/urllib/request.py                                           | 2 +-
 .../next/Security/2021-01-31-05-28-14.bpo-43075.DoAXqO.rst      | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Security/2021-01-31-05-28-14.bpo-43075.DoAXqO.rst

diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index 6624e04317ba2..56565405a7097 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -947,7 +947,7 @@ class AbstractBasicAuthHandler:
     # (single quotes are a violation of the RFC, but appear in the wild)
     rx = re.compile('(?:^|,)'   # start of the string or ','
                     '[ \t]*'    # optional whitespaces
-                    '([^ \t]+)' # scheme like "Basic"
+                    '([^ \t,]+)' # scheme like "Basic"
                     '[ \t]+'    # mandatory whitespaces
                     # realm=xxx
                     # realm='xxx'
diff --git a/Misc/NEWS.d/next/Security/2021-01-31-05-28-14.bpo-43075.DoAXqO.rst b/Misc/NEWS.d/next/Security/2021-01-31-05-28-14.bpo-43075.DoAXqO.rst
new file mode 100644
index 0000000000000..1c9f727e965fb
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2021-01-31-05-28-14.bpo-43075.DoAXqO.rst
@@ -0,0 +1 @@
+Fix Regular Expression Denial of Service (ReDoS) vulnerability in :class:`urllib.request.AbstractBasicAuthHandler`.  The ReDoS-vulnerable regex has quadratic worst-case complexity and it allows cause a denial of service when identifying crafted invalid RFCs. This ReDoS issue is on the client side and needs remote attackers to control the HTTP server.