The check_privacy_settings AJAX action of the WordPress GDPR WordPress plugin before 1.9.27 available to both unauthenticated and authenticated users responds with JSON data without an \application/json\ content-type. Since an HTML payload isn't properly escaped it may be interpreted by a web browser led to this endpoint. Javascript code may be executed on a victim's browser. Due to v1.9.26 adding a CSRF check the XSS is only exploitable against unauthenticated users (as they all share the same nonce)