Easy!Appointments through 1.6.0 Authorization Bypass via booking/register Endpoint

Easy!Appointments through 1.6.0 contains an authorization bypass vulnerability in Booking::register() that allows unauthenticated attackers to modify any appointment by supplying an appointment id without its hash. Attackers can enumerate sequential appointment ids with a self-asserted manage_mode flag to rewrite appointment details, rebind them to attacker-controlled customers, and obtain management hashes for rescheduling or cancellation.