[5.1.x] Fixed CVE-2025-64458 -- Mitigated potential DoS in HttpResponseRedirect/HttpResponsePermanentRedirect on Windows.

Thanks Seokchan Yoon for the report, Markus Holtermann for the
triage, and Jake Howard for the review.

Follow-up to CVE-2025-27556 and 39e2297210d9d2938c75fc911d45f0e863dc4821.

Backport of c880530ddd4fabd5939bab0e148bebe36699432a from main.

4 files changed, 27 insertions, 4 deletions

diff --git a/django/http/response.py b/django/http/response.py
index eecd972cd6..eaeccdc97a 100644
--- a/django/http/response.py
+++ b/django/http/response.py
@@ -21,7 +21,7 @@ from django.http.cookie import SimpleCookie
 from django.utils import timezone
 from django.utils.datastructures import CaseInsensitiveMapping
 from django.utils.encoding import iri_to_uri
-from django.utils.http import content_disposition_header, http_date
+from django.utils.http import MAX_URL_LENGTH, content_disposition_header, http_date
 from django.utils.regex_helper import _lazy_re_compile
 
 _charset_from_content_type_re = _lazy_re_compile(
@@ -616,7 +616,12 @@ class HttpResponseRedirectBase(HttpResponse):
     def __init__(self, redirect_to, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self["Location"] = iri_to_uri(redirect_to)
-        parsed = urlparse(str(redirect_to))
+        redirect_to_str = str(redirect_to)
+        if len(redirect_to_str) > MAX_URL_LENGTH:
+            raise DisallowedRedirect(
+                f"Unsafe redirect exceeding {MAX_URL_LENGTH} characters"
+            )
+        parsed = urlparse(redirect_to_str)
         if parsed.scheme and parsed.scheme not in self.allowed_schemes:
             raise DisallowedRedirect(
                 "Unsafe redirect to URL with protocol '%s'" % parsed.scheme
diff --git a/docs/releases/4.2.26.txt b/docs/releases/4.2.26.txt
index e0db257c04..ae274c3361 100644
--- a/docs/releases/4.2.26.txt
+++ b/docs/releases/4.2.26.txt
@@ -7,4 +7,12 @@ Django 4.2.26 release notes
 Django 4.2.26 fixes one security issue with severity "high" and one security
 issue with severity "moderate" in 4.2.25.
 
-...
+CVE-2025-64458: Potential denial-of-service vulnerability in ``HttpResponseRedirect`` and ``HttpResponsePermanentRedirect`` on Windows
+======================================================================================================================================
+
+Python's :func:`NFKC normalization <python:unicodedata.normalize>` is slow on
+Windows. As a consequence, :class:`~django.http.HttpResponseRedirect`,
+:class:`~django.http.HttpResponsePermanentRedirect`, and the shortcut
+:func:`redirect() <django.shortcuts.redirect>` were subject to a potential
+denial-of-service attack via certain inputs with a very large number of Unicode
+characters (follow up to :cve:`2025-27556`).
diff --git a/docs/releases/5.1.14.txt b/docs/releases/5.1.14.txt
index 79a7a260e3..8dba96e487 100644
--- a/docs/releases/5.1.14.txt
+++ b/docs/releases/5.1.14.txt
@@ -7,4 +7,12 @@ Django 5.1.14 release notes
 Django 5.1.14 fixes one security issue with severity "high" and one security
 issue with severity "moderate" in 5.1.13.
 
-...
+CVE-2025-64458: Potential denial-of-service vulnerability in ``HttpResponseRedirect`` and ``HttpResponsePermanentRedirect`` on Windows
+======================================================================================================================================
+
+Python's :func:`NFKC normalization <python:unicodedata.normalize>` is slow on
+Windows. As a consequence, :class:`~django.http.HttpResponseRedirect`,
+:class:`~django.http.HttpResponsePermanentRedirect`, and the shortcut
+:func:`redirect() <django.shortcuts.redirect>` were subject to a potential
+denial-of-service attack via certain inputs with a very large number of Unicode
+characters (follow up to :cve:`2025-27556`).
diff --git a/tests/httpwrappers/tests.py b/tests/httpwrappers/tests.py
index 2197c6f7ea..9d23c59e10 100644
--- a/tests/httpwrappers/tests.py
+++ b/tests/httpwrappers/tests.py
@@ -24,6 +24,7 @@ from django.http import (
 )
 from django.test import SimpleTestCase
 from django.utils.functional import lazystr
+from django.utils.http import MAX_URL_LENGTH
 
 
 class QueryDictTests(SimpleTestCase):
@@ -490,6 +491,7 @@ class HttpResponseTests(SimpleTestCase):
             'data:text/html,<script>window.alert("xss")</script>',
             "mailto:test@example.com",
             "file:///etc/passwd",
+            "é" * (MAX_URL_LENGTH + 1),
         ]
         for url in bad_urls:
             with self.assertRaises(DisallowedRedirect):