The User Registration & Membership WordPress plugin before 5.2.2 does not verify the authenticity of incoming payment-provider webhook notifications before acting on them, allowing unauthenticated attackers to forge a payment-approved event and activate a paid membership subscription without completing a real payment.
https://wpscan.com/vulnerability/faf55649-8f76-4abf-a6b9-0d0774e22d29/