UserPro <= 5.1.6 - Disabled Membership Registration Bypass

The UserPro plugin for WordPress is vulnerable to Security Feature Bypass in all versions up to, and including, 5.1.6. This is due to the use of client-side restrictions to enforce the 'Disabled registration' Membership feature within the plugin's General settings. This makes it possible for unauthenticated attackers to register an account even when account registration has been disabled by an administrator.