The Ultimate Member WordPress plugin before 2.13.0 does not validate a submitted role selection...

The Ultimate Member WordPress plugin before 2.13.0 does not validate a submitted role selection when it cannot resolve the set of roles a profile form permits, and screens the value against the site's registered role names rather than against the form's own allow-list, allowing unauthenticated users who register through the Ultimate Member WordPress plugin before 2.13.0's own form to grant themselves arbitrary capabilities and reach administrator-equivalent access.