User Registration & Membership <= 5.1.2 - Insecure Direct Object Reference to Unauthenticated Limited User Deletion

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, 5.1.2 via the 'register_member' function, due to missing validation on the 'member_id' user controlled key. This makes it possible for unauthenticated attackers to delete arbitrary user accounts that newly registered on the site who has the 'urm_user_just_created' user meta set.