File CVE-2021-45115.patch of Package python-Django

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File CVE-2021-45115.patch of Package python-Django

From 144022e6efeebc776372029e3426f182ae006b1d Mon Sep 17 00:00:00 2001
From: Florian Apolloner <florian@apolloner.eu>
Date: Mon, 27 Dec 2021 14:48:03 +0100
Subject: [PATCH] [2.2.x] Fixed CVE-2021-45115 -- Prevented DoS vector in
 UserAttributeSimilarityValidator.

Thanks Chris Bailey for the report.

Co-authored-by: Adam Johnson <me@adamj.eu>
---
 django/contrib/auth/password_validation.py | 40 ++++++++++++++++++++--
 docs/releases/2.2.26.txt                   | 14 +++++++-
 docs/topics/auth/passwords.txt             | 14 +++++---
 tests/auth_tests/test_validators.py        | 11 +++---
 4 files changed, 65 insertions(+), 14 deletions(-)

diff --git a/django/contrib/auth/password_validation.py b/django/contrib/auth/password_validation.py
index 948ded6dbc..a80214ded7 100644
--- a/django/contrib/auth/password_validation.py
+++ b/django/contrib/auth/password_validation.py
@@ -120,6 +120,36 @@ class MinimumLengthValidator:
         ) % {'min_length': self.min_length}
 
 
+def exceeds_maximum_length_ratio(password, max_similarity, value):
+    """
+    Test that value is within a reasonable range of password.
+
+    The following ratio calculations are based on testing SequenceMatcher like
+    this:
+
+    for i in range(0,6):
+      print(10**i, SequenceMatcher(a='A', b='A'*(10**i)).quick_ratio())
+
+    which yields:
+
+    1 1.0
+    10 0.18181818181818182
+    100 0.019801980198019802
+    1000 0.001998001998001998
+    10000 0.00019998000199980003
+    100000 1.999980000199998e-05
+
+    This means a length_ratio of 10 should never yield a similarity higher than
+    0.2, for 100 this is down to 0.02 and for 1000 it is 0.002. This can be
+    calculated via 2 / length_ratio. As a result we avoid the potentially
+    expensive sequence matching.
+    """
+    pwd_len = len(password)
+    length_bound_similarity = max_similarity / 2 * pwd_len
+    value_len = len(value)
+    return pwd_len >= 10 * value_len and value_len < length_bound_similarity
+
+
 class UserAttributeSimilarityValidator(object):
     """
     Validate whether the password is sufficiently different from the user's
@@ -135,19 +165,25 @@ class UserAttributeSimilarityValidator:
 
     def __init__(self, user_attributes=DEFAULT_USER_ATTRIBUTES, max_similarity=0.7):
         self.user_attributes = user_attributes
+        if max_similarity < 0.1:
+            raise ValueError('max_similarity must be at least 0.1')
         self.max_similarity = max_similarity
 
     def validate(self, password, user=None):
         if not user:
             return
 
+        password = password.lower()
         for attribute_name in self.user_attributes:
             value = getattr(user, attribute_name, None)
             if not value or not isinstance(value, string_types):
                 continue
-            value_parts = re.split(r'\W+', value) + [value]
+            value_lower = value.lower()
+            value_parts = re.split(r'\W+', value_lower) + [value_lower]
             for value_part in value_parts:
-                if SequenceMatcher(a=password.lower(), b=value_part.lower()).quick_ratio() >= self.max_similarity:
+                if exceeds_maximum_length_ratio(password, self.max_similarity, value_part):
+                    continue
+                if SequenceMatcher(a=password, b=value_part).quick_ratio() >= self.max_similarity:
                     try:
                         verbose_name = force_text(user._meta.get_field(attribute_name).verbose_name)
                     except FieldDoesNotExist:
diff --git a/docs/topics/auth/passwords.txt b/docs/topics/auth/passwords.txt
index bcf20a976d..c509a3a522 100644
--- a/docs/topics/auth/passwords.txt
+++ b/docs/topics/auth/passwords.txt
@@ -545,10 +545,16 @@ Django includes four validators:
     is used: ``'username', 'first_name', 'last_name', 'email'``.
     Attributes that don't exist are ignored.
 
-    The minimum similarity of a rejected password can be set on a scale of 0 to
-    1 with the ``max_similarity`` parameter. A setting of 0 rejects all
-    passwords, whereas a setting of 1 rejects only passwords that are identical
-    to an attribute's value.
+    The maximum allowed similarity of passwords can be set on a scale of 0.1
+    to 1.0 with the ``max_similarity`` parameter. This is compared to the
+    result of :meth:`difflib.SequenceMatcher.quick_ratio`. A value of 0.1
+    rejects passwords unless they are substantially different from the
+    ``user_attributes``, whereas a value of 1.0 rejects only passwords that are
+    identical to an attribute's value.
+
+    .. versionchanged:: 2.2.26
+
+        The ``max_similarity`` parameter was limited to a minimum value of 0.1.
 
 .. class:: CommonPasswordValidator(password_list_path=DEFAULT_PASSWORD_LIST_PATH)
 
diff --git a/tests/auth_tests/test_validators.py b/tests/auth_tests/test_validators.py
index 1c2c6b4aff..777e51ebde 100644
--- a/tests/auth_tests/test_validators.py
+++ b/tests/auth_tests/test_validators.py
@@ -132,13 +132,10 @@ class UserAttributeSimilarityValidatorTest(TestCase):
                 max_similarity=1,
             ).validate(user.first_name, user=user)
         self.assertEqual(cm.exception.messages, [expected_error % "first name"])
-        # max_similarity=0 rejects all passwords.
-        with self.assertRaises(ValidationError) as cm:
-            UserAttributeSimilarityValidator(
-                user_attributes=['first_name'],
-                max_similarity=0,
-            ).validate('XXX', user=user)
-        self.assertEqual(cm.exception.messages, [expected_error % "first name"])
+        # Very low max_similarity is rejected.
+        msg = 'max_similarity must be at least 0.1'
+        with self.assertRaisesMessage(ValueError, msg):
+            UserAttributeSimilarityValidator(max_similarity=0.09)
         # Passes validation.
         self.assertIsNone(
             UserAttributeSimilarityValidator(user_attributes=['first_name']).validate('testclient', user=user)
-- 
2.31.1

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