The HivePress Authentication plugin for WordPress is vulnerable to Authentication Bypass via the access_token parameter in all versions up to, and including, 1.1.4. This is due to the authenticate_user function's Facebook authenticator resolving third-party identity by forwarding the attacker-supplied access_token to the Facebook Graph API and trusting the returned email and ID verbatim, without performing any application ID or audience validation — specifically, no /debug_token verification and no comparison of the token's app_id against the configured hp_facebook_app_id. This makes it possible for unauthenticated attackers to authenticate as any existing WordPress user, including administrators, whose email address is associated with a Facebook account for which the attacker can obtain any valid access token. Important Note: To exploit the vulnerability, the attacker must obtain the victim's access token.
https://plugins.trac.wordpress.org/changeset/3664231/hivepress-authentication
https://developers.facebook.com/docs/facebook-login/guides/advanced/manual-flow/#confirm