WWBN AVideo is an open source video platform. In versions up to and including 26.0, the `categories.json.php` endpoint, which serves the category listing API, fails to enforce user group-based access controls on categories. In the default request path (no `?user=` parameter), user group filtering is entirely skipped, exposing all non-private categories including those restricted to specific user groups. When the `?user=` parameter is supplied, a type confusion bug causes the filter to use the admin user's (user_id=1) group memberships instead of the current user's, rendering the filter ineffective. Commit 6e8a673eed07be5628d0b60fbfabd171f3ce74c9 contains a fix.