The User Registration & Membership – Custom Registration Form, Login Form, and User Profile plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 4.1.3 via the user_registration_membership_register_member() due to missing validation on the 'membership_id' user controlled key. This makes it possible for unauthenticated attackers to update any user's membership to any other active or non-active membership type.
CWE-639