[Python-checkins] bpo-43075: Fix ReDoS in urllib AbstractBasicAuthHandler (GH-24391) (GH-25247)

[vstinner]

https://github.com/python/cpython/commit/a21d4fbd549ec9685068a113660553d7f80d9b09
commit: a21d4fbd549ec9685068a113660553d7f80d9b09
branch: 3.9
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: vstinner <vstinner at python.org>
date: 2021-04-07T17:58:04+02:00
summary:

bpo-43075: Fix ReDoS in urllib AbstractBasicAuthHandler (GH-24391) (GH-25247)

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 at ios.ac.cn>

Co-authored-by: Yeting Li <liyt at ios.ac.cn>

files:
A Misc/NEWS.d/next/Security/2021-01-31-05-28-14.bpo-43075.DoAXqO.rst
M Lib/urllib/request.py

diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index 57d991465a5b0..af3fb9ca54a0b 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -943,7 +943,7 @@ 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.