[2.2.x] Fixed CVE-2020-24584 -- Fixed permission escalation in intermediate-level directories of the file system cache on Python 3.7+.

Backport of f56b57976133129b0b351a38bba4ac882badabf0 from master.

django/core/cache/backends/filebased.py

@@ -114,10 +114,15 @@ class FileBasedCache(BaseCache):
 
     def _createdir(self):
         if not os.path.exists(self._dir):
+            # Set the umask because os.makedirs() doesn't apply the "mode" argument
+            # to intermediate-level directories.
+            old_umask = os.umask(0o077)
             try:
                 os.makedirs(self._dir, 0o700)
             except FileExistsError:
                 pass
+            finally:
+                os.umask(old_umask)
 
     def _key_to_file(self, key, version=None):
         """

docs/releases/2.2.16.txt

@@ -4,7 +4,7 @@ Django 2.2.16 release notes
 
 *Expected September 1, 2020*
 
-Django 2.2.16 fixes a security issue and two data loss bugs in 2.2.15.
+Django 2.2.16 fixes two security issues and two data loss bugs in 2.2.15.
 
 CVE-2020-24583: Incorrect permissions on intermediate-level directories on Python 3.7+
 ======================================================================================
@@ -17,6 +17,13 @@ files and to intermediate-level collected static directories when using the
 You should review and manually fix permissions on existing intermediate-level
 directories.
 
+CVE-2020-24584: Permission escalation in intermediate-level directories of the file system cache on Python 3.7+
+===============================================================================================================
+
+On Python 3.7+, the intermediate-level directories of the file system cache had
+the system's standard umask rather than ``0o077`` (no group or others
+permissions).
+
 Bugfixes
 ========
 

tests/cache/tests.py

@@ -6,11 +6,13 @@ import os
 import pickle
 import re
 import shutil
+import sys
 import tempfile
 import threading
 import time
 import unittest
-from unittest import mock
+from pathlib import Path
+from unittest import mock, skipIf
 
 from django.conf import settings
 from django.core import management, signals
@@ -1430,6 +1432,28 @@ class FileBasedCacheTests(BaseCacheTests, TestCase):
         # Returns the default instead of erroring.
         self.assertEqual(cache.get('foo', 'baz'), 'baz')
 
+    @skipIf(
+        sys.platform == 'win32',
+        'Windows only partially supports umasks and chmod.',
+    )
+    def test_cache_dir_permissions(self):
+        os.rmdir(self.dirname)
+        dir_path = Path(self.dirname) / 'nested' / 'filebasedcache'
+        for cache_params in settings.CACHES.values():
+            cache_params['LOCATION'] = str(dir_path)
+        setting_changed.send(self.__class__, setting='CACHES', enter=False)
+        cache.set('foo', 'bar')
+        self.assertIs(dir_path.exists(), True)
+        tests = [
+            dir_path,
+            dir_path.parent,
+            dir_path.parent.parent,
+        ]
+        for directory in tests:
+            with self.subTest(directory=directory):
+                dir_mode = directory.stat().st_mode & 0o777
+                self.assertEqual(dir_mode, 0o700)
+
     def test_get_does_not_ignore_non_filenotfound_exceptions(self):
         with mock.patch('builtins.open', side_effect=IOError):
             with self.assertRaises(IOError):