The WPBookit plugin for WordPress is vulnerable to privilege escalation via account takeover in all versions up to, and including, 1.0.2. This is due to the plugin not properly validating a user's identity prior to updating their details like email through the edit_newdata_customer_callback() function. This makes it possible for unauthenticated attackers to change arbitrary user's email addresses, including administrators, and leverage that to reset the user's password and gain access to their account.
The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.