[3.1.x] Fixed #30530, CVE-2021-44420 -- Fixed potential bypass of an upstream access control based on URL paths.

Thanks Sjoerd Job Postmus and TengMA(@te3t123) for reports.

Backport of d4dcd5b9dd9e462fec8220e33e3e6c822b7e88a6 from main.

4 files changed, 29 insertions, 4 deletions

diff --git a/django/urls/resolvers.py b/django/urls/resolvers.py
index e565d34b27..abf0a11572 100644
--- a/django/urls/resolvers.py
+++ b/django/urls/resolvers.py
@@ -153,7 +153,11 @@ class RegexPattern(CheckURLMixin):
         self.converters = {}
 
     def match(self, path):
-        match = self.regex.search(path)
+        match = (
+            self.regex.fullmatch(path)
+            if self._is_endpoint and self.regex.pattern.endswith('$')
+            else self.regex.search(path)
+        )
         if match:
             # If there are any named groups, use those as kwargs, ignoring
             # non-named groups. Otherwise, pass all non-named arguments as
@@ -240,7 +244,7 @@ def _route_to_regex(route, is_endpoint=False):
         converters[parameter] = converter
         parts.append('(?P<' + parameter + '>' + converter.regex + ')')
     if is_endpoint:
-        parts.append('$')
+        parts.append(r'\Z')
     return ''.join(parts), converters
 
 
diff --git a/docs/releases/2.2.25.txt b/docs/releases/2.2.25.txt
index e8e552d80e..1662451a30 100644
--- a/docs/releases/2.2.25.txt
+++ b/docs/releases/2.2.25.txt
@@ -6,4 +6,8 @@ Django 2.2.25 release notes
 
 Django 2.2.25 fixes a security issue with severity "low" in 2.2.24.
 
-...
+CVE-2021-44420: Potential bypass of an upstream access control based on URL paths
+=================================================================================
+
+HTTP requests for URLs with trailing newlines could bypass an upstream access
+control based on URL paths.
diff --git a/docs/releases/3.1.14.txt b/docs/releases/3.1.14.txt
index 45775c3ce6..fb6fef8884 100644
--- a/docs/releases/3.1.14.txt
+++ b/docs/releases/3.1.14.txt
@@ -6,4 +6,8 @@ Django 3.1.14 release notes
 
 Django 3.1.14 fixes a security issue with severity "low" in 3.1.13.
 
-...
+CVE-2021-44420: Potential bypass of an upstream access control based on URL paths
+=================================================================================
+
+HTTP requests for URLs with trailing newlines could bypass an upstream access
+control based on URL paths.
diff --git a/tests/urlpatterns/tests.py b/tests/urlpatterns/tests.py
index 54b7e09813..98866f0b79 100644
--- a/tests/urlpatterns/tests.py
+++ b/tests/urlpatterns/tests.py
@@ -147,6 +147,19 @@ class SimplifiedURLTests(SimpleTestCase):
         with self.assertRaisesMessage(ImproperlyConfigured, msg):
             path('space/<int: num>', empty_view)
 
+    def test_path_trailing_newlines(self):
+        tests = [
+            '/articles/2003/\n',
+            '/articles/2010/\n',
+            '/en/foo/\n',
+            '/included_urls/extra/\n',
+            '/regex/1/\n',
+            '/users/1/\n',
+        ]
+        for url in tests:
+            with self.subTest(url=url), self.assertRaises(Resolver404):
+                resolve(url)
+
 
 @override_settings(ROOT_URLCONF='urlpatterns.converter_urls')
 class ConverterTests(SimpleTestCase):