ProfilePress < 4.16.18 - Unauthenticated Privilege Escalation via Registration Role Selection

The Paid Membership Plugin, Ecommerce, User Registration Form, Login Form, User Profile & Restrict Content WordPress plugin before 4.16.18 does not consistently enforce the role restriction configured on its front-end registration role-selection field. The set of roles offered to the visitor and the set of roles the registration handler accepts are derived by two different parsers, and for some valid ways of configuring the offered roles the handler ignores the restriction and falls back to accepting any non-administrator role. Combined with the absence of a nonce on the public registration handler, this allows an unauthenticated visitor to register an account with a higher role, such as Editor or Author, than the form was configured to offer.