The plugin is lacking any capability and CSRF check when saving it's settings, allowing any authenticated users (such as subscriber) to change them. If users can't register, this can be done through CSRF. Furthermore, the cookie banner setting is not sanitised or validated before being output in all pages of the frontend and the backend settings one, leading to a Stored Cross-Site Scripting issue.
Proof of Concept
POST /wp-admin/admin-ajax.php HTTP/1.1
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Cookie: [Any authenticated user / via CSRF]