security: fix CVE-2023-26481 (#4832)

fix CVE-2023-26481

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

authentik/flows/views/executor.py

@@ -162,7 +162,7 @@ class FlowExecutorView(APIView):
             token.delete()
         if not isinstance(plan, FlowPlan):
             return None
-        plan.context[PLAN_CONTEXT_IS_RESTORED] = True
+        plan.context[PLAN_CONTEXT_IS_RESTORED] = token
         self._logger.debug("f(exec): restored flow plan from token", plan=plan)
         return plan
 

authentik/stages/email/stage.py

@@ -15,7 +15,7 @@ from authentik.flows.challenge import Challenge, ChallengeResponse, ChallengeTyp
 from authentik.flows.models import FlowToken
 from authentik.flows.planner import PLAN_CONTEXT_IS_RESTORED, PLAN_CONTEXT_PENDING_USER
 from authentik.flows.stage import ChallengeStageView
-from authentik.flows.views.executor import QS_KEY_TOKEN, SESSION_KEY_GET
+from authentik.flows.views.executor import QS_KEY_TOKEN
 from authentik.stages.email.models import EmailStage
 from authentik.stages.email.tasks import send_mails
 from authentik.stages.email.utils import TemplateEmailMessage
@@ -103,12 +103,14 @@ class EmailStageView(ChallengeStageView):
 
     def get(self, request: HttpRequest, *args, **kwargs) -> HttpResponse:
         # Check if the user came back from the email link to verify
-        if QS_KEY_TOKEN in request.session.get(
+        restore_token: FlowToken = self.executor.plan.context.get(PLAN_CONTEXT_IS_RESTORED, None)
-            SESSION_KEY_GET, {}
+        user = self.get_pending_user()
-        ) and self.executor.plan.context.get(PLAN_CONTEXT_IS_RESTORED, False):
+        if restore_token:
+            if restore_token.user != user:
+                self.logger.warning("Flow token for non-matching user, denying request")
+                return self.executor.stage_invalid()
             messages.success(request, _("Successfully verified Email."))
             if self.executor.current_stage.activate_user_on_success:
-                user = self.get_pending_user()
                 user.is_active = True
                 user.save()
             return self.executor.stage_ok()

authentik/stages/email/tests/test_stage.py

@@ -7,10 +7,9 @@ from django.core.mail.backends.smtp import EmailBackend as SMTPEmailBackend
 from django.urls import reverse
 from django.utils.http import urlencode
 
-from authentik.core.models import Token
 from authentik.core.tests.utils import create_test_admin_user, create_test_flow
 from authentik.flows.markers import StageMarker
-from authentik.flows.models import FlowDesignation, FlowStageBinding
+from authentik.flows.models import FlowDesignation, FlowStageBinding, FlowToken
 from authentik.flows.planner import PLAN_CONTEXT_PENDING_USER, FlowPlan
 from authentik.flows.tests import FlowTestCase
 from authentik.flows.views.executor import QS_KEY_TOKEN, SESSION_KEY_PLAN
@@ -134,7 +133,7 @@ class TestEmailStage(FlowTestCase):
         session = self.client.session
         session[SESSION_KEY_PLAN] = plan
         session.save()
-        token: Token = Token.objects.get(user=self.user)
+        token: FlowToken = FlowToken.objects.get(user=self.user)
 
         with patch("authentik.flows.views.executor.FlowExecutorView.cancel", MagicMock()):
             # Call the executor shell to preseed the session
@@ -165,3 +164,43 @@ class TestEmailStage(FlowTestCase):
             plan: FlowPlan = session[SESSION_KEY_PLAN]
             self.assertEqual(plan.context[PLAN_CONTEXT_PENDING_USER], self.user)
             self.assertTrue(plan.context[PLAN_CONTEXT_PENDING_USER].is_active)
+
+    def test_token_invalid_user(self):
+        """Test with token with invalid user"""
+        # Make sure token exists
+        self.test_pending_user()
+        self.user.is_active = False
+        self.user.save()
+        plan = FlowPlan(flow_pk=self.flow.pk.hex, bindings=[self.binding], markers=[StageMarker()])
+        session = self.client.session
+        session[SESSION_KEY_PLAN] = plan
+        session.save()
+        # Set flow token user to a different user
+        token: FlowToken = FlowToken.objects.get(user=self.user)
+        token.user = create_test_admin_user()
+        token.save()
+
+        with patch("authentik.flows.views.executor.FlowExecutorView.cancel", MagicMock()):
+            # Call the executor shell to preseed the session
+            url = reverse(
+                "authentik_api:flow-executor",
+                kwargs={"flow_slug": self.flow.slug},
+            )
+            url_query = urlencode(
+                {
+                    QS_KEY_TOKEN: token.key,
+                }
+            )
+            url += f"?query={url_query}"
+            self.client.get(url)
+
+            # Call the actual executor to get the JSON Response
+            response = self.client.get(
+                reverse(
+                    "authentik_api:flow-executor",
+                    kwargs={"flow_slug": self.flow.slug},
+                )
+            )
+
+            self.assertEqual(response.status_code, 200)
+            self.assertStageResponse(response, component="ak-stage-access-denied")

blueprints/example/flows-recovery-email-verification.yaml

@@ -154,6 +154,7 @@ entries:
       policy: !KeyOf default-recovery-skip-if-restored
       target: !KeyOf flow-binding-email
       order: 0
+    state: absent
     model: authentik_policies.policybinding
     attrs:
       negate: false

website/docs/policies/expression.mdx

@@ -99,7 +99,7 @@ This includes the following:
 -   `context['application']`: The application the user is in the process of authorizing. (Optional)
 -   `context['source']`: The source the user is authenticating/enrolling with. (Optional)
 -   `context['pending_user']`: The currently pending user, see [User](../user-group/user.md#object-attributes)
--   `context['is_restored']`: Set to `True` when the flow plan has been restored from a flow token, for example the user clicked a link to a flow which was sent by an email stage. (Optional)
+-   `context['is_restored']`: Contains the flow token when the flow plan was restored from a link, for example the user clicked a link to a flow which was sent by an email stage. (Optional)
 -   `context['auth_method']`: Authentication method (this value is set by password stages) (Optional)
 
     Depending on method, `context['auth_method_args']` is also set.

website/docs/security/CVE-2023-26481.md

@@ -0,0 +1,27 @@
+# CVE-2023-26481
+
+_Reported by [@fuomag9](https://github.com/fuomag9)_
+
+## Insufficient user check in FlowTokens by Email stage
+
+### Summary
+
+Due to an insufficient access check, a recovery flow link that is created by an admin (or sent via email by an admin) can be used to set the password for any arbitrary user.
+
+### Patches
+
+authentik 2022.12.3, 2023.1.3, 2023.2.3 fix this issue.
+
+### Impact
+
+This attack is only possible if a recovery flow exists, which has both an Identification and an Email stage bound to it. If the flow has policies on the identification stage to skip it when the flow is restored (by checking `request.context['is_restored']`), the flow is not affected by this. With this flow in place, an administrator must create a recovery Link or send a recovery URL to the attacker, who can, due to the improper validation of the token create, set the password for any account.
+
+### Workaround
+
+It is recommended to upgrade to the patched version of authentik. Regardless, for custom recovery flows it is recommended to add a policy that checks if the flow is restored, and skips the identification stage.
+
+### For more information
+
+If you have any questions or comments about this advisory:
+
+-   Email us at [security@goauthentik.io](mailto:security@goauthentik.io)

website/sidebars.js

@@ -300,9 +300,10 @@ module.exports = {
             },
             items: [
                 "security/policy",
+                "security/CVE-2022-23555",
                 "security/CVE-2022-46145",
                 "security/CVE-2022-46172",
-                "security/CVE-2022-23555",
+                "security/CVE-2023-26481",
             ],
         },
     ],