CVE-2026-52839: Easy!Appointments appointments/store and appointments/update allow cross-provider appointment injection — Authorization Bypass

Easy!Appointments correctly filters provider-scoped appointments in the appointments/search response, proving that provider isolation is an intended security boundary. However, the direct mutation endpoints appointments/store and appointments/update only check generic appointment privileges and never verify that the submitted id_users_provider belongs to the current session.

A normal authenticated provider can inject new appointments into another provider’s schedule via store, or reassign existing appointments into a foreign provider’s calendar via update. The store path contains an additional write-before-crash bug: the unauthorized row is committed to the database before the controller crashes on a type error, so the attacker receives an error response while the foreign appointment is already persisted.