The Registration Forms – User Registration Forms, Invitation-Based Registrations, Front-end User Profile, Login Form & Content Restriction Social Sites Login plugin for WordPress is vulnerable to authentication bypass in all versions up to, and including, 1.7.9. This is due to insufficient verification on the user being returned by the social login token. This makes it possible for unauthenticated attackers to log in as any existing user on the site, such as an administrator, if they have access to the email and the user does not have an already-existing account for the service returning the token.
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.