From 20293be1fd671edc7fec675c78fc1cf9e05b98f4 Mon Sep 17 00:00:00 2001
From: Benedikt Johannes <benedikt.johannes.hofer@gmail.com>
Date: Fri, 6 Mar 2026 13:22:21 +0100
Subject: [PATCH] gh-144370: Disallow usage of control characters in status in
 wsgiref.handlers for security (GH-144371)

Disallow usage of control characters in status in wsgiref.handlers
to prevent HTTP header injections.
(cherry picked from commit d931725bc850cd096f6703bc285e885f1e015f05)

Co-authored-by: Benedikt Johannes <benedikt.johannes.hofer@gmail.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>
---
 Lib/test/test_wsgiref.py                      | 19 +++++++++++++++++++
 Lib/wsgiref/handlers.py                       |  4 +++-
 Misc/ACKS                                     |  1 +
 ...-01-31-21-56-54.gh-issue-144370.fp9m8t.rst |  2 ++
 4 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Security/2026-01-31-21-56-54.gh-issue-144370.fp9m8t.rst

diff --git a/Lib/test/test_wsgiref.py b/Lib/test/test_wsgiref.py
index bb575bdaef62a2..a8b03d15130791 100644
--- a/Lib/test/test_wsgiref.py
+++ b/Lib/test/test_wsgiref.py
@@ -855,6 +855,25 @@ def write(self, b):
         self.assertIsNotNone(h.status)
         self.assertIsNotNone(h.environ)
 
+    def testRaisesControlCharacters(self):
+        for c0 in control_characters_c0():
+            with self.subTest(c0):
+                base = BaseHandler()
+                with self.assertRaises(ValueError):
+                    base.start_response(c0, [('x', 'y')])
+
+                base = BaseHandler()
+                with self.assertRaises(ValueError):
+                    base.start_response('200 OK', [(c0, 'y')])
+
+                # HTAB (\x09) is allowed in header values, but not in names.
+                base = BaseHandler()
+                if c0 != "\t":
+                    with self.assertRaises(ValueError):
+                        base.start_response('200 OK', [('x', c0)])
+                else:
+                    base.start_response('200 OK', [('x', c0)])
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Lib/wsgiref/handlers.py b/Lib/wsgiref/handlers.py
index cafe872c7aae9b..f8fe89f6e13436 100644
--- a/Lib/wsgiref/handlers.py
+++ b/Lib/wsgiref/handlers.py
@@ -1,7 +1,7 @@
 """Base classes for server/gateway implementations"""
 
 from .util import FileWrapper, guess_scheme, is_hop_by_hop
-from .headers import Headers
+from .headers import Headers, _name_disallowed_re
 
 import sys, os, time
 
@@ -249,6 +249,8 @@ def start_response(self, status, headers,exc_info=None):
         return self.write
 
     def _validate_status(self, status):
+        if _name_disallowed_re.search(status):
+            raise ValueError("Control characters are not allowed in status")
         if len(status) < 4:
             raise AssertionError("Status must be at least 4 characters")
         if not status[:3].isdigit():
diff --git a/Misc/ACKS b/Misc/ACKS
index a6e63a991f9288..022718b9333886 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1041,6 +1041,7 @@ Wolfgang Langner
 Detlef Lannert
 Rémi Lapeyre
 Soren Larsen
+Seth Michael Larson
 Amos Latteier
 Piers Lauder
 Ben Laurie
diff --git a/Misc/NEWS.d/next/Security/2026-01-31-21-56-54.gh-issue-144370.fp9m8t.rst b/Misc/NEWS.d/next/Security/2026-01-31-21-56-54.gh-issue-144370.fp9m8t.rst
new file mode 100644
index 00000000000000..2d13a0611322c5
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2026-01-31-21-56-54.gh-issue-144370.fp9m8t.rst
@@ -0,0 +1,2 @@
+Disallow usage of control characters in status in :mod:`wsgiref.handlers` to prevent HTTP header injections.
+Patch by Benedikt Johannes.