KiviCare <= 4.4.0 - Missing Authorization to Unauthenticated Payment Bypass and Appointment Status Manipulation via /payment-success REST Endpoint

The KiviCare – Clinic & Patient Management System (EHR) plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 4.4.0. This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for unauthenticated attackers to mark arbitrary pending appointments as Confirmed and forge an associated completed payment record in wp_kc_payments_appointment_mappings using an attacker-supplied payment ID, bypassing payment entirely. This exploit is achievable on a default installation because the gateway resolution logic returns all registered gateways regardless of admin-enabled status, making the manual (KCPayLater) gateway always selectable.