The Booking for Appointments and Events Calendar – Amelia (Premium) plugin for WordPress is vulnerable to Privilege Escalation in versions 8.0 - 9.6.2. This is due to insufficient validation of the attacker-controlled 'type' parameter in the customer update endpoint, which allows customers to set their role to 'manager' and trigger creation of a WordPress user with the wpamelia-manager role when the 'externalId' parameter is set to 0. This makes it possible for unauthenticated attackers to escalate their privileges to administrator by first elevating to the manager role, then creating a provider entity linked to an administrator user ID and overwriting that administrator's password.