User Registration & Membership < 5.2.8 - Subscriber+ Privilege Escalation via Membership Purchase

The User Registration & Membership WordPress plugin before 5.2.8 does not check the capability of the user making a membership purchase, and does not validate the payment method or the plan submitted with it, allowing any authenticated user such as a subscriber to be granted the WordPress role attached to a paid plan without paying for it. Where the site owner has mapped a plan to a privileged role, this leads to privilege escalation up to administrator.