The Easy Appointments WordPress plugin before 4.0.2.2 does not use an unguessable token to authorize its mail-link appointment cancellation and confirmation action, deriving the token from a hardcoded source-embedded salt and the appointment's creation timestamp, so unauthenticated attackers who know or guess that timestamp can cancel or confirm arbitrary appointments.
https://wpscan.com/vulnerability/b498fba8-8969-45af-8cef-e91d6be34912/