Username enumeration attack in goauthentik

@@ -12,7 +12,7 @@
 from rest_framework.serializers import ValidationError
 
 from authentik.flows.challenge import Challenge, ChallengeResponse, ChallengeTypes
-from authentik.flows.models import FlowToken
+from authentik.flows.models import FlowDesignation, 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
@@ -82,6 +82,11 @@ def send_email(self):
         """Helper function that sends the actual email. Implies that you've
         already checked that there is a pending user."""
         pending_user = self.get_pending_user()
+        if not pending_user.pk and self.executor.flow.designation == FlowDesignation.RECOVERY:
+            # Pending user does not have a primary key, and we're in a recovery flow,
+            # which means the user entered an invalid identifier, so we pretend to send the
+            # email, to not disclose if the user exists
+            return
         email = self.executor.plan.context.get(PLAN_CONTEXT_EMAIL_OVERRIDE, None)
         if not email:
             email = pending_user.email

@@ -5,18 +5,20 @@
 from django.core import mail
 from django.core.mail.backends.locmem import EmailBackend
 from django.urls import reverse
-from rest_framework.test import APITestCase
 
+from authentik.core.models import User
 from authentik.core.tests.utils import create_test_admin_user, create_test_flow
 from authentik.events.models import Event, EventAction
 from authentik.flows.markers import StageMarker
 from authentik.flows.models import FlowDesignation, FlowStageBinding
 from authentik.flows.planner import PLAN_CONTEXT_PENDING_USER, FlowPlan
+from authentik.flows.tests import FlowTestCase
 from authentik.flows.views.executor import SESSION_KEY_PLAN
+from authentik.lib.generators import generate_id
 from authentik.stages.email.models import EmailStage
 
 
-class TestEmailStageSending(APITestCase):
+class TestEmailStageSending(FlowTestCase):
     """Email tests"""
 
     def setUp(self):
@@ -44,6 +46,13 @@ def test_pending_user(self):
         ):
             response = self.client.post(url)
             self.assertEqual(response.status_code, 200)
+            self.assertStageResponse(
+                response,
+                self.flow,
+                response_errors={
+                    "non_field_errors": [{"string": "email-sent", "code": "email-sent"}]
+                },
+            )
             self.assertEqual(len(mail.outbox), 1)
             self.assertEqual(mail.outbox[0].subject, "authentik")
             events = Event.objects.filter(action=EventAction.EMAIL_SENT)
@@ -54,6 +63,32 @@ def test_pending_user(self):
             self.assertEqual(event.context["to_email"], [self.user.email])
             self.assertEqual(event.context["from_email"], "system@authentik.local")
 
+    def test_pending_fake_user(self):
+        """Test with pending (fake) user"""
+        self.flow.designation = FlowDesignation.RECOVERY
+        self.flow.save()
+        plan = FlowPlan(flow_pk=self.flow.pk.hex, bindings=[self.binding], markers=[StageMarker()])
+        plan.context[PLAN_CONTEXT_PENDING_USER] = User(username=generate_id())
+        session = self.client.session
+        session[SESSION_KEY_PLAN] = plan
+        session.save()
+
+        url = reverse("authentik_api:flow-executor", kwargs={"flow_slug": self.flow.slug})
+        with patch(
+            "authentik.stages.email.models.EmailStage.backend_class",
+            PropertyMock(return_value=EmailBackend),
+        ):
+            response = self.client.post(url)
+            self.assertEqual(response.status_code, 200)
+            self.assertStageResponse(
+                response,
+                self.flow,
+                response_errors={
+                    "non_field_errors": [{"string": "email-sent", "code": "email-sent"}]
+                },
+            )
+            self.assertEqual(len(mail.outbox), 0)
+
     def test_send_error(self):
         """Test error during sending (sending will be retried)"""
         plan = FlowPlan(flow_pk=self.flow.pk.hex, bindings=[self.binding], markers=[StageMarker()])

@@ -118,8 +118,12 @@ def validate(self, attrs: dict[str, Any]) -> dict[str, Any]:
                 username=uid_field,
                 email=uid_field,
             )
+            self.pre_user = self.stage.executor.plan.context[PLAN_CONTEXT_PENDING_USER]
             if not current_stage.show_matched_user:
                 self.stage.executor.plan.context[PLAN_CONTEXT_PENDING_USER_IDENTIFIER] = uid_field
+            if self.stage.executor.flow.designation == FlowDesignation.RECOVERY:
+                # When used in a recovery flow, always continue to not disclose if a user exists
+                return attrs
             raise ValidationError("Failed to authenticate.")
         self.pre_user = pre_user
         if not current_stage.password_stage:

@@ -188,7 +188,7 @@ def test_enrollment_flow(self):
             ],
         )
 
-    def test_recovery_flow(self):
+    def test_link_recovery_flow(self):
         """Test that recovery flow is linked correctly"""
         flow = create_test_flow()
         self.stage.recovery_flow = flow
@@ -226,6 +226,38 @@ def test_recovery_flow(self):
             ],
         )
 
+    def test_recovery_flow_invalid_user(self):
+        """Test that an invalid user can proceed in a recovery flow"""
+        self.flow.designation = FlowDesignation.RECOVERY
+        self.flow.save()
+        response = self.client.get(
+            reverse("authentik_api:flow-executor", kwargs={"flow_slug": self.flow.slug}),
+        )
+        self.assertStageResponse(
+            response,
+            self.flow,
+            component="ak-stage-identification",
+            user_fields=["email"],
+            password_fields=False,
+            show_source_labels=False,
+            primary_action="Continue",
+            sources=[
+                {
+                    "challenge": {
+                        "component": "xak-flow-redirect",
+                        "to": "/source/oauth/login/test/",
+                        "type": ChallengeTypes.REDIRECT.value,
+                    },
+                    "icon_url": "/static/authentik/sources/default.svg",
+                    "name": "test",
+                }
+            ],
+        )
+        form_data = {"uid_field": generate_id()}
+        url = reverse("authentik_api:flow-executor", kwargs={"flow_slug": self.flow.slug})
+        response = self.client.post(url, form_data)
+        self.assertEqual(response.status_code, 200)
+
     def test_api_validate(self):
         """Test API validation"""
         self.assertTrue(

@@ -152,6 +152,10 @@ image:
 
 -   \*: fix [CVE-2023-36456](../security/CVE-2023-36456), Reported by [@thijsa](https://github.com/thijsa)
 
+## Fixed in 2023.5.6
+
+-   \*: fix [CVE-2023-39522](../security/CVE-2023-39522), Reported by [@markrassamni](https://github.com/markrassamni)
+
 ## API Changes
 
 #### What's Changed

@@ -88,6 +88,10 @@ helm upgrade authentik authentik/authentik -f values.yaml --version ^2023.6
 -   sources/ldap: fix more errors (#6191)
 -   sources/ldap: fix page size (#6187)
 
+## Fixed in 2023.6.2
+
+-   \*: fix [CVE-2023-39522](../security/CVE-2023-39522), Reported by [@markrassamni](https://github.com/markrassamni)
+
 ## API Changes
 
 #### What's New

@@ -0,0 +1,27 @@
+# CVE-2023-39522
+
+_Reported by [@markrassamni](https://github.com/markrassamni)_
+
+## Username enumeration attack
+
+### Summary
+
+Using a recovery flow with an identification stage an attacker is able to determine if a username exists.
+
+### Patches
+
+authentik 2023.5.6 and 2023.6.2 fix this issue.
+
+### Impact
+
+Only setups configured with a recovery flow are impacted by this.
+
+### Details
+
+An attacker can easily enumerate and check users' existence using the recovery flow, as a clear message is shown when a user doesn't exist. Depending on configuration this can either be done by username, email, or both.
+
+### For more information
+
+If you have any questions or comments about this advisory:
+
+-   Email us at [security@goauthentik.io](mailto:security@goauthentik.io)

@@ -361,6 +361,7 @@ const docsSidebar = {
             },
             items: [
                 "security/policy",
+                "security/CVE-2023-39522",
                 "security/CVE-2023-36456",
                 "security/2023-06-cure53",
                 "security/CVE-2023-26481",