CVE-2026-40165

@@ -231,12 +231,12 @@ def _handle_name_id_transient(self) -> SourceFlowManager:
         user has an attribute that refers to our Source for cleanup. The user is also deleted
         on logout and periodically."""
         # Create a temporary User
-        name_id = self._get_name_id()
+        name_id_el, name_id = self._get_name_id()
         expiry = mktime(
             (now() + timedelta_from_string(self._source.temporary_user_delete_after)).timetuple()
         )
         user: User = User.objects.create(
-            username=name_id.text,
+            username=name_id,
             attributes={
                 USER_ATTRIBUTE_GENERATED: True,
                 USER_ATTRIBUTE_SOURCES: [
@@ -247,20 +247,18 @@ def _handle_name_id_transient(self) -> SourceFlowManager:
             },
             path=self._source.get_user_path(),
         )
-        LOGGER.debug("Created temporary user for NameID Transient", username=name_id.text)
+        LOGGER.debug("Created temporary user for NameID Transient", username=name_id)
         user.set_unusable_password()
         user.save()
-        UserSAMLSourceConnection.objects.create(
-            source=self._source, user=user, identifier=name_id.text
-        )
+        UserSAMLSourceConnection.objects.create(source=self._source, user=user, identifier=name_id)
         return SAMLSourceFlowManager(
             source=self._source,
             request=self._http_request,
-            identifier=str(name_id.text),
+            identifier=str(name_id),
             user_info={
                 "root": self._root,
                 "assertion": self.get_assertion(),
-                "name_id": name_id,
+                "name_id": name_id_el,
             },
             policy_context={},
         )
@@ -271,7 +269,7 @@ def get_assertion(self) -> _Element | None:
             return self._assertion
         return self._root.find(f"{{{NS_SAML_ASSERTION}}}Assertion")
 
-    def _get_name_id(self) -> _Element:
+    def _get_name_id(self) -> tuple[_Element, str]:
         """Get NameID Element"""
         assertion = self.get_assertion()
         if assertion is None:
@@ -282,12 +280,11 @@ def _get_name_id(self) -> _Element:
         name_id = subject.find(f"{{{NS_SAML_ASSERTION}}}NameID")
         if name_id is None:
             raise ValueError("NameID element not found")
-        return name_id
+        return name_id, "".join(name_id.itertext())
 
     def _get_name_id_filter(self) -> dict[str, str]:
         """Returns the subject's NameID as a Filter for the `User`"""
-        name_id_el = self._get_name_id()
-        name_id = name_id_el.text
+        name_id_el, name_id = self._get_name_id()
         if not name_id:
             raise UnsupportedNameIDFormat("Subject's NameID is empty.")
         _format = name_id_el.attrib["Format"]
@@ -308,26 +305,26 @@ def _get_name_id_filter(self) -> dict[str, str]:
 
     def prepare_flow_manager(self) -> SourceFlowManager:
         """Prepare flow plan depending on whether or not the user exists"""
-        name_id = self._get_name_id()
+        name_id_el, name_id = self._get_name_id()
         # Sanity check, show a warning if NameIDPolicy doesn't match what we go
-        if self._source.name_id_policy != name_id.attrib["Format"]:
+        if self._source.name_id_policy != name_id_el.attrib["Format"]:
             LOGGER.warning(
                 "NameID from IdP doesn't match our policy",
                 expected=self._source.name_id_policy,
-                got=name_id.attrib["Format"],
+                got=name_id_el.attrib["Format"],
             )
         # transient NameIDs are handled separately as they don't have to go through flows.
-        if name_id.attrib["Format"] == SAML_NAME_ID_FORMAT_TRANSIENT:
+        if name_id_el.attrib["Format"] == SAML_NAME_ID_FORMAT_TRANSIENT:
             return self._handle_name_id_transient()
 
         return SAMLSourceFlowManager(
             source=self._source,
             request=self._http_request,
-            identifier=str(name_id.text),
+            identifier=name_id,
             user_info={
                 "root": self._root,
                 "assertion": self.get_assertion(),
-                "name_id": name_id,
+                "name_id": name_id_el,
             },
             policy_context={
                 "saml_response": etree.tostring(self._root),

@@ -193,8 +193,33 @@ def test_verification_assertion_duplicate(self):
 
         parser = ResponseProcessor(self.source, request)
         parser.parse()
-        self.assertNotEqual(parser._get_name_id().text, "bad")
-        self.assertEqual(parser._get_name_id().text, "_ce3d2948b4cf20146dee0a0b3dd6f69b6cf86f62d7")
+        self.assertNotEqual(parser._get_name_id()[1], "bad")
+        self.assertEqual(parser._get_name_id()[1], "_ce3d2948b4cf20146dee0a0b3dd6f69b6cf86f62d7")
+
+    @freeze_time("2022-10-14T14:15:00")
+    def test_name_id_comment(self):
+        """Test comment in name ID"""
+        fixture = load_fixture("fixtures/response_signed_assertion_dup.xml")
+        fixture = fixture.replace(
+            "_ce3d2948b4cf20146dee0a0b3dd6f69b6cf86f62d7",
+            "_ce3d2948b4cf20146dee0a0b3dd6f<!--x-->69b6cf86f62d7",
+        )
+        key = load_fixture("fixtures/signature_cert.pem")
+        kp = CertificateKeyPair.objects.create(
+            name=generate_id(),
+            certificate_data=key,
+        )
+        self.source.verification_kp = kp
+        self.source.signed_assertion = True
+        self.source.signed_response = False
+        request = self.factory.post(
+            "/",
+            data={"SAMLResponse": b64encode(fixture.encode()).decode()},
+        )
+
+        parser = ResponseProcessor(self.source, request)
+        parser.parse()
+        self.assertEqual(parser._get_name_id()[1], "_ce3d2948b4cf20146dee0a0b3dd6f69b6cf86f62d7")
 
     @freeze_time("2014-07-17T01:02:18Z")
     def test_verification_response(self):

@@ -0,0 +1,33 @@
+# CVE-2026-40165
+
+_Reported by [@kodareef5](https://github.com/kodareef5), [@Android-Login-Analysis](https://github.com/Android-Login-Analysis), and [@AyushParkara](https://github.com/AyushParkara)_
+
+## SAML Source Fails to Validate Assertion Conditions
+
+### Summary
+
+Due to how authentik used to extract the NameID value from a SAML assertion, it was possible for an attacker to trick authentik into only seeing a part of the NameID value, potentially allowing an attacker to get access to other accounts.
+
+### Patches
+
+authentik 2025.12.5 and 2026.2.3 fix this issue, for other versions the workaround below can be used.
+
+### Impact
+
+This issue can be exploited given an authentik instance with a SAML Source, where the attacker has an account on the SAML Source and the ability to modify their NameID value (commonly username or E-mail), and XML Signing is enabled. The attacker can modify the SAML assertion given to authentik by injecting a comment within the NameID value, which effectively truncates the NameID value to the snippet before the comment, and give the attack access to any user account.
+
+### Workarounds
+
+Create a SAML Source property mapping with the following expression and add it to all SAML Sources:
+
+```python
+if name_id.text != "".join(name_id.itertext()):
+  raise ValueError("Mismatched NameID")
+return {}
+```
+
+### For more information
+
+If you have any questions or comments about this advisory:
+
+- Email us at [security@goauthentik.io](mailto:security@goauthentik.io).