The Frontend Login and Registration Blocks plugin for WordPress is vulnerable to privilege escalation via account takeover in all versions up to, and including, 1.0.7. This is due to the plugin not properly validating a user's identity prior to updating their details like email via the flr_blocks_user_settings_handle_ajax_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.