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, 2.11.10. This is due to the 'wcfmvm_membership_change' AJAX action not validating user permission to modify other users. This makes it possible for authenticated attackers, with vendor level access and above, to change any user's role to 'wcfm_vendor' by changing their membership plan.