The Paid Memberships Pro plugin for WordPress is a piece of software that is vulnerable to malicious activity. Up to and including version 2.12.3, it has an issue with file type validation that makes it possible for people with certain permissions to upload files to the site. This could allow someone to put code onto the server that could be executed remotely. This is only possible if either 2Checkout (which is not supported after version 2.6) or PayPal Express is used for payments and a custom user field is added that only appears when a user is viewing their profile, but not when they are checking out.