The Paid Membership Subscriptions – Effortless Memberships, Recurring Payments & Content Restriction plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 2.13.7. This is due to the pms_pb_payment_redirect_link function using the user-controlled value supplied via the 'pms_payment_id' parameter to authenticate users without any further identity validation. This makes it possible for unauthenticated attackers with knowledge of a valid payment ID to log in as any user who has made a purchase on the targeted site.