RegistrationMagic 5.0.1.8 - 6.0.9.8 - Unauthenticated Authentication Bypass via Missing Facebook Token Audience Validation

Description

The plugin does not verify which application a Facebook access token was issued to before accepting it as proof of identity, allowing unauthenticated attackers to log in as an existing user whose token they can obtain, or to create and log into a new account even when user registration is disabled.

Disabling the plugin's Facebook login option does not prevent this: the setting guards only the login button, not the code path that accepts the token.