WP Booking System <= 2.1.0.3 - Missing Authorization to Authenticated (Subscriber+) Privilege Escalation via 'user_permission' Parameter via Cross-Form Nonce Reuse

The WP Booking System – Booking Calendar plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 2.1.0.3 This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for authenticated attackers, with subscriber-level access and above, to grant themselves and arbitrary other users edit access to every booking form on the site by overwriting the user_permission meta that governs the plugin's own access-control list. Exploitation requires the attacker to have already been delegated edit rights on at least one booking form, as this delegation both downgrades the submenu capability to 'read' (making the edit page accessible) and allows them to harvest a valid wpbs_edit_form nonce that will pass validation against any other form_id.