The Paid Membership Subscriptions WordPress plugin before 3.1.0 does not verify the reCAPTCHA on its registration handler when a form field is absent from the request, allowing unauthenticated users to create accounts without solving the reCAPTCHA the site has enabled.
https://wpscan.com/vulnerability/685f381e-97b5-4855-a0ca-5854043a7b9e/