gh-144370: Disallow usage of control characters in status in wsgiref.handlers for security (#144371)

Disallow usage of control characters in status in wsgiref.handlers
to prevent HTTP header injections.

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>

Author: 3 people

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)])
+
 
 class TestModule(unittest.TestCase):
     def test_deprecated__version__(self):

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
 
@@ -250,6 +250,8 @@ 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():

Misc/ACKS

@@ -1086,6 +1086,7 @@ Wolfgang Langner
 Detlef Lannert
 Rémi Lapeyre
 Soren Larsen
+Seth Michael Larson
 Amos Latteier
 Keenan Lau
 Piers Lauder

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.