User Registration & Membership <= 5.2.8 - Cross-Site Request Forgery to trigger_bulk_action()

The User Registration & Membership – Free & Paid Memberships, Subscriptions, Content Restriction, User Profile, Custom User Registration & Login Builder plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 5.2.8 This is due to missing or incorrect nonce validation on the trigger_bulk_action function. This makes it possible for unauthenticated attackers to force administrators to approve pending user registrations or deny arbitrary user accounts, locking targeted users out of the site via a forged request granted they can trick a site administrator into performing an action such as clicking on a link. An attacker can bypass the earlier nonce check in trigger_query_actions() by supplying an empty new_role parameter, which causes that handler to return early and cede control to the unprotected trigger_bulk_action() handler; the exit() call at the end of that handler additionally prevents WordPress core's own bulk-users nonce validation from executing.