The WCFM Membership – WooCommerce Memberships for Multivendor Marketplace plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 2.11.8 via the 'WCFMvm_Memberships_Payment_Controller::processing' due to missing validation on a user controlled key. This makes it possible for authenticated attackers, with Subscriber-level access and above, to modify other users' membership payments.