GP Premium <= 2.4.0 - Cross-Site Scripting

The GP Premium plugin for WordPress up to 2.4.0 is vulnerable to reflected XSS via the 'message' parameter in inc/verify.php lines 95-101, where a message passed with slactivation=false is URL-decoded and used unsanitized in addsettingserror, allowing XSS payloads to be reflected in admin notices...