The Registration Forms – User Registration Forms, Invitation-Based Registrations, Front-end User Profile, Login Form & Content Restriction plugin for WordPress is vulnerable to unauthorized arbitrary plugin installation and activation/deactivation due to missing capability checks on the pieregister_install_addon, pieregister_activate_addon and pieregister_deactivate_addon functions in all versions up to, and including, 3.8.3.4. This makes it possible for authenticated attackers, with Subscriber-level access and above, to install, activate and deactivate arbitrary plugins. As a result attackers might achieve code execution on the targeted server