Harden revoke access token for password changes

Author: sevdog

rest_framework_simplejwt/authentication.py

@@ -2,6 +2,7 @@
 
 from django.contrib.auth import get_user_model
 from django.contrib.auth.models import AbstractBaseUser
+from django.utils.crypto import constant_time_compare
 from django.utils.translation import gettext_lazy as _
 from rest_framework import HTTP_HEADER_ENCODING, authentication
 from rest_framework.request import Request
@@ -10,7 +11,7 @@
 from .models import TokenUser
 from .settings import api_settings
 from .tokens import Token
-from .utils import get_md5_hash_password
+from .utils import get_fallback_token_auth_hash, get_token_auth_hash
 
 AUTH_HEADER_TYPES = api_settings.AUTH_HEADER_TYPES
 
@@ -135,9 +136,17 @@ def get_user(self, validated_token: Token) -> AuthUser:
             raise AuthenticationFailed(_("User is inactive"), code="user_inactive")
 
         if api_settings.CHECK_REVOKE_TOKEN:
-            if validated_token.get(
-                api_settings.REVOKE_TOKEN_CLAIM
-            ) != get_md5_hash_password(user.password):
+            validation_claim = validated_token.get(api_settings.REVOKE_TOKEN_CLAIM)
+            if (
+                validation_claim is None
+                or not constant_time_compare(
+                    validation_claim, get_token_auth_hash(user)
+                )
+                and not any(
+                    constant_time_compare(validation_claim, fallback_auth_hash)
+                    for fallback_auth_hash in get_fallback_token_auth_hash(user)
+                )
+            ):
                 raise AuthenticationFailed(
                     _("The user's password has been changed."), code="password_changed"
                 )

rest_framework_simplejwt/tokens.py

@@ -16,7 +16,7 @@
     datetime_from_epoch,
     datetime_to_epoch,
     format_lazy,
-    get_md5_hash_password,
+    get_token_auth_hash,
 )
 
 if TYPE_CHECKING:
@@ -208,9 +208,7 @@ def for_user(cls, user: AuthUser) -> "Token":
         token[api_settings.USER_ID_CLAIM] = user_id
 
         if api_settings.CHECK_REVOKE_TOKEN:
-            token[api_settings.REVOKE_TOKEN_CLAIM] = get_md5_hash_password(
-                user.password
-            )
+            token[api_settings.REVOKE_TOKEN_CLAIM] = get_token_auth_hash(user)
 
         return token
 

rest_framework_simplejwt/utils.py

@@ -1,18 +1,44 @@
-import hashlib
 from calendar import timegm
 from datetime import datetime, timezone
-from typing import Callable
+from typing import TYPE_CHECKING, Callable, TypeVar
 
 from django.conf import settings
+from django.contrib.auth.models import AbstractBaseUser
+from django.utils.crypto import salted_hmac
 from django.utils.functional import lazy
 from django.utils.timezone import is_naive, make_aware
 
+if TYPE_CHECKING:
+    from .models import TokenUser
 
-def get_md5_hash_password(password: str) -> str:
+    AuthUser = TypeVar("AuthUser", AbstractBaseUser, TokenUser)
+
+
+def _get_token_auth_hash(user: "AuthUser", secret=None) -> str:
+    key_salt = "rest_framework_simplejwt.utils.get_token_auth_hash"
+    return salted_hmac(key_salt, user.password, secret=secret).hexdigest()
+
+
+def get_token_auth_hash(user: "AuthUser") -> str:
     """
-    Returns MD5 hash of the given password
+    Return an HMAC of the given user password field.
     """
-    return hashlib.md5(password.encode()).hexdigest().upper()
+    if hasattr(user, "get_session_auth_hash"):
+        return user.get_session_auth_hash()
+    return _get_token_auth_hash(user)
+
+
+def get_fallback_token_auth_hash(user: "AuthUser") -> str:
+    """
+    Yields a sequence of fallback HMACs of the given user password field.
+    """
+    if hasattr(user, "get_session_auth_fallback_hash"):
+        yield from user.get_session_auth_fallback_hash()
+
+    fallback_keys = getattr(settings, "SECRET_KEY_FALLBACKS", [])
+    yield from (
+        _get_token_auth_hash(user, fallback_secret) for fallback_secret in fallback_keys
+    )
 
 
 def make_utc(dt: datetime) -> datetime:

tests/conftest.py

@@ -16,6 +16,10 @@ def pytest_configure():
         },
         SITE_ID=1,
         SECRET_KEY="not very secret in tests",
+        SECRET_KEY_FALLBACKS=[
+            "old not very secure secret",
+            "other old not very secure secret",
+        ],
         USE_I18N=True,
         STATIC_URL="/static/",
         ROOT_URLCONF="tests.urls",

tests/test_authentication.py

@@ -10,7 +10,7 @@
 from rest_framework_simplejwt.models import TokenUser
 from rest_framework_simplejwt.settings import api_settings
 from rest_framework_simplejwt.tokens import AccessToken, SlidingToken
-from rest_framework_simplejwt.utils import get_md5_hash_password
+from rest_framework_simplejwt.utils import _get_token_auth_hash, get_token_auth_hash
 
 from .utils import override_api_settings
 
@@ -145,60 +145,47 @@ def test_get_user(self):
         with self.assertRaises(AuthenticationFailed):
             self.backend.get_user(payload)
 
-        u = User.objects.create_user(username="markhamill")
-        u.is_active = False
-        u.save()
+        user = User.objects.create_user(username="markhamill", is_active=False)
 
-        payload[api_settings.USER_ID_CLAIM] = getattr(u, api_settings.USER_ID_FIELD)
+        payload[api_settings.USER_ID_CLAIM] = getattr(user, api_settings.USER_ID_FIELD)
 
         # Should raise exception if user is inactive
         with self.assertRaises(AuthenticationFailed):
             self.backend.get_user(payload)
 
-        u.is_active = True
-        u.save()
+        user.is_active = True
+        user.save()
 
         # Otherwise, should return correct user
-        self.assertEqual(self.backend.get_user(payload).id, u.id)
+        self.assertEqual(self.backend.get_user(payload).id, user.id)
 
     @override_api_settings(
         CHECK_REVOKE_TOKEN=True, REVOKE_TOKEN_CLAIM="revoke_token_claim"
     )
     def test_get_user_with_check_revoke_token(self):
-        payload = {"some_other_id": "foo"}
-
-        # Should raise error if no recognizable user identification
-        with self.assertRaises(InvalidToken):
-            self.backend.get_user(payload)
-
-        payload[api_settings.USER_ID_CLAIM] = 42
-
-        # Should raise exception if user not found
-        with self.assertRaises(AuthenticationFailed):
-            self.backend.get_user(payload)
-
-        u = User.objects.create_user(username="markhamill")
-        u.is_active = False
-        u.save()
+        user = User.objects.create_user(username="markhamill")
+        payload = {
+            api_settings.USER_ID_CLAIM: getattr(user, api_settings.USER_ID_FIELD)
+        }
 
-        payload[api_settings.USER_ID_CLAIM] = getattr(u, api_settings.USER_ID_FIELD)
-
-        # Should raise exception if user is inactive
+        # Should raise exception if claim is missing
         with self.assertRaises(AuthenticationFailed):
             self.backend.get_user(payload)
 
-        u.is_active = True
-        u.save()
-
-        # Should raise exception if hash password is different
+        payload[api_settings.REVOKE_TOKEN_CLAIM] = "differenthash"
+        # Should raise exception if claim is different
         with self.assertRaises(AuthenticationFailed):
             self.backend.get_user(payload)
 
-        if api_settings.CHECK_REVOKE_TOKEN:
-            payload[api_settings.REVOKE_TOKEN_CLAIM] = get_md5_hash_password(u.password)
+        payload[api_settings.REVOKE_TOKEN_CLAIM] = _get_token_auth_hash(
+            user, "other old not very secure secret"
+        )
+        # Should return correct user if claim was signed with an old key
+        self.assertEqual(self.backend.get_user(payload).id, user.id)
 
+        payload[api_settings.REVOKE_TOKEN_CLAIM] = get_token_auth_hash(user)
         # Otherwise, should return correct user
-        self.assertEqual(self.backend.get_user(payload).id, u.id)
+        self.assertEqual(self.backend.get_user(payload).id, user.id)
 
 
 class TestJWTStatelessUserAuthentication(TestCase):