Eventin < 4.1.24 - Unauthenticated Order and Attendee Status Reset via Payment REST Endpoint

The Eventin WordPress plugin before 4.1.24 does not properly authorise order finalisation when its offline (local) payment method is enabled, relying on a nonce that is exposed to unauthenticated visitors and never checking that the caller owns the order, allowing unauthenticated attackers to reset any existing order and its attendees to a pending state and thereby invalidate paid tickets.