MotoPress Hotel Booking <= 6.0.1 - Missing Authorization to Unauthenticated Arbitrary Booking Notes Modification via mphb_update_booking_notes AJAX Action

The MotoPress Hotel Booking plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 6.0.1. This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for unauthenticated attackers to overwrite or delete the internal notes (_mphb_booking_internal_notes) of any booking by supplying an arbitrary booking ID. The nonce for this action is output in the HTML source of every public page through wp_localize_script (MPHB._data.nonces), so any unauthenticated visitor can obtain a valid nonce and perform the action without any account or prior interaction.