The Bookit — Booking & Appointment Calendar WordPress plugin before 2.6.0.1 does not properly restrict the data returned by an availability-check request, allowing unauthenticated users to retrieve other customers' appointment details, including free-text booking comments and contact information.
https://wpscan.com/vulnerability/5a6f6d75-e7b8-44ad-a0f6-f6e4938ac3d5/