The WPCOM Member plugin for WordPress is vulnerable to authentication bypass in all versions up to, and including, 1.7.5. This is due to insufficient verification on the user_phone parameter when logging in. This makes it possible for unauthenticated attackers to log in as any existing user on the site, such as an administrator, if SMS login is enabled.
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.