ClipBucket v5 has IDOR in Collection Item Management

ClipBucket v5 is an open source video sharing platform. Prior to version 5.5.3 #59, collection item operations are vulnerable to authorization flaws, allowing a normal authenticated user to modify another user’s collection items. This affects both add item (/actions/add_to_collection.php) due to missing authorization checks and delete item (/manage_collections.php?mode=manage_items...) due to a broken ownership check in removeItemFromCollection(). As a result, attackers can insert and remove items from collections they do not own. Version 5.5.3 #59 fixes the issue.