Fixed #37095 -- Checked maximum redirect lengths against percent-encoded URLs.

2 files changed, 15 insertions, 3 deletions

diff --git a/django/http/response.py b/django/http/response.py
index 45fb0177d1..17b8da4da1 100644
--- a/django/http/response.py
+++ b/django/http/response.py
@@ -642,12 +642,11 @@ class HttpResponseRedirectBase(HttpResponse):
     ):
         super().__init__(*args, **kwargs)
         self["Location"] = iri_to_uri(redirect_to)
-        redirect_to_str = str(redirect_to)
-        if max_length is not None and len(redirect_to_str) > max_length:
+        if max_length is not None and len(self["Location"]) > max_length:
             raise DisallowedRedirect(
                 f"Unsafe redirect exceeding {max_length} characters"
             )
-        parsed = urlsplit(redirect_to_str)
+        parsed = urlsplit(str(redirect_to))
         if preserve_request:
             self.status_code = self.status_code_preserve_request
         if parsed.scheme and parsed.scheme not in self.allowed_schemes:
diff --git a/tests/httpwrappers/tests.py b/tests/httpwrappers/tests.py
index b990e9f816..151088909c 100644
--- a/tests/httpwrappers/tests.py
+++ b/tests/httpwrappers/tests.py
@@ -24,6 +24,7 @@ from django.http import (
     parse_cookie,
 )
 from django.test import SimpleTestCase
+from django.utils.encoding import iri_to_uri
 from django.utils.functional import lazystr
 from django.utils.http import MAX_URL_REDIRECT_LENGTH
 
@@ -498,6 +499,18 @@ class HttpResponseTests(SimpleTestCase):
                 response = response_class(long_url)
                 self.assertEqual(response.url, long_url)
 
+    def test_redirect_url_max_length_checks_encoded_location(self):
+        long_url = "/" + "é" * (MAX_URL_REDIRECT_LENGTH - 1)
+        self.assertLessEqual(len(long_url), MAX_URL_REDIRECT_LENGTH)
+        self.assertGreater(len(iri_to_uri(long_url)), MAX_URL_REDIRECT_LENGTH)
+        for response_class in (HttpResponseRedirect, HttpResponsePermanentRedirect):
+            msg = f"Unsafe redirect exceeding {MAX_URL_REDIRECT_LENGTH} characters"
+            with (
+                self.subTest(response_class=response_class),
+                self.assertRaisesMessage(DisallowedRedirect, msg),
+            ):
+                response_class(long_url)
+
     def test_redirect_url_max_length_override_via_param(self):
         base_url = "https://example.com/"
         for (max_length, length), response_class in itertools.product(