providers/oauth2: fix CVE-2024-21637 (#8104)

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

authentik/providers/oauth2/tests/test_authorize.py

@@ -87,6 +87,25 @@ class TestAuthorize(OAuthTestCase):
             )
             OAuthAuthorizationParams.from_request(request)
 
+    def test_blocked_redirect_uri(self):
+        """test missing/invalid redirect URI"""
+        OAuth2Provider.objects.create(
+            name=generate_id(),
+            client_id="test",
+            authorization_flow=create_test_flow(),
+            redirect_uris="data:local.invalid",
+        )
+        with self.assertRaises(RedirectUriError):
+            request = self.factory.get(
+                "/",
+                data={
+                    "response_type": "code",
+                    "client_id": "test",
+                    "redirect_uri": "data:localhost",
+                },
+            )
+            OAuthAuthorizationParams.from_request(request)
+
     def test_invalid_redirect_uri_empty(self):
         """test missing/invalid redirect URI"""
         provider = OAuth2Provider.objects.create(

authentik/providers/oauth2/views/authorize.py

@@ -76,6 +76,7 @@ PLAN_CONTEXT_PARAMS = "goauthentik.io/providers/oauth2/params"
 SESSION_KEY_LAST_LOGIN_UID = "authentik/providers/oauth2/last_login_uid"
 
 ALLOWED_PROMPT_PARAMS = {PROMPT_NONE, PROMPT_CONSENT, PROMPT_LOGIN}
+FORBIDDEN_URI_SCHEMES = {"javascript", "data", "vbscript"}
 
 
 @dataclass(slots=True)
@@ -179,6 +180,10 @@ class OAuthAuthorizationParams:
         self.check_scope(github_compat)
         self.check_nonce()
         self.check_code_challenge()
+        if self.request:
+            raise AuthorizeError(
+                self.redirect_uri, "request_not_supported", self.grant_type, self.state
+            )
 
     def check_redirect_uri(self):
         """Redirect URI validation."""
@@ -216,10 +221,9 @@ class OAuthAuthorizationParams:
                     redirect_uri_expected=allowed_redirect_urls,
                 )
                 raise RedirectUriError(self.redirect_uri, allowed_redirect_urls)
-        if self.request:
+        # Check against forbidden schemes
-            raise AuthorizeError(
+        if urlparse(self.redirect_uri).scheme in FORBIDDEN_URI_SCHEMES:
-                self.redirect_uri, "request_not_supported", self.grant_type, self.state
+            raise RedirectUriError(self.redirect_uri, allowed_redirect_urls)
-            )
 
     def check_scope(self, github_compat=False):
         """Ensure openid scope is set in Hybrid flows, or when requesting an id_token"""

authentik/providers/oauth2/views/token.py

@@ -6,6 +6,7 @@ from hashlib import sha256
 from re import error as RegexError
 from re import fullmatch
 from typing import Any, Optional
+from urllib.parse import urlparse
 
 from django.http import HttpRequest, HttpResponse
 from django.utils import timezone
@@ -55,6 +56,7 @@ from authentik.providers.oauth2.models import (
     RefreshToken,
 )
 from authentik.providers.oauth2.utils import TokenResponse, cors_allow, extract_client_auth
+from authentik.providers.oauth2.views.authorize import FORBIDDEN_URI_SCHEMES
 from authentik.sources.oauth.models import OAuthSource
 from authentik.stages.password.stage import PLAN_CONTEXT_METHOD, PLAN_CONTEXT_METHOD_ARGS
 
@@ -206,6 +208,10 @@ class TokenParams:
                 ).from_http(request)
                 raise TokenError("invalid_client")
 
+        # Check against forbidden schemes
+        if urlparse(self.redirect_uri).scheme in FORBIDDEN_URI_SCHEMES:
+            raise TokenError("invalid_request")
+
         self.authorization_code = AuthorizationCode.objects.filter(code=raw_code).first()
         if not self.authorization_code:
             LOGGER.warning("Code does not exist", code=raw_code)

website/docs/security/CVE-2024-21637.md

@@ -0,0 +1,39 @@
+# CVE-2024-21637
+
+_Reported by [@lauritzh](https://github.com/lauritzh)_
+
+## XSS in Authentik via JavaScript-URI as Redirect URI and form_post Response Mode
+
+### Summary
+
+Given an OAuth2 provider configured with allowed redirect URIs set to `*` or `.*`, an attacker can send an OAuth Authorization request using `response_mode=form_post` and setting `redirect_uri` to a malicious URI, to capture authentik's session token.
+
+### Patches
+
+authentik 2023.8.6 and 2023.10.6 fix this issue.
+
+### Impact
+
+The impact depends on the attack scenario. In the following I will describe the two scenario that were identified for Authentik.
+
+#### Redirect URI Misconfiguration
+
+While advising that this may cause security issues, Authentik generally allows wildcards as Redirect URI. Therefore, using a wildcard-only effectively allowing arbitrary URLS is possible misconfiguration that may be present in real-world instances.
+
+In such cases, unauthenticated and unprivileged attackers can perform the above described actions.
+
+### User with (only) App Administration Permissions
+
+A more likely scenario is an administrative user (e.g. a normal developer) having only permissions to manage applications.
+
+This relatively user could use the described attacks to perform a privilege escalation.
+
+### Workaround
+
+It is recommended to upgrade to the patched version of authentik. If not possible, ensure that OAuth2 providers do not use a wildcard (`*` or `.*`) value as allowed redirect URI setting. (This is _not_ exploitable if part of the redirect URI has a wildcard, for example `https://foo-.*\.bar\.com`)
+
+### 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

@@ -408,6 +408,7 @@ const docsSidebar = {
             },
             items: [
                 "security/policy",
+                "security/CVE-2024-21637",
                 "security/CVE-2023-48228",
                 "security/GHSA-rjvp-29xq-f62w",
                 "security/CVE-2023-39522",