Salon Booking System – Free Version <= 10.30.33 - Unauthenticated Google Calendar Connection Hijack via OAuth Callback

The Salon Booking System WordPress plugin through 10.30.33 does not perform any capability check or validate an OAuth state value on its Google Calendar authorization callback, which is also hooked for unauthenticated users, allowing an unauthenticated attacker to overwrite the site's stored Google Calendar connection tokens with attacker-controlled ones and hijack the integration. Exploitation requires the site to have configured its own Google OAuth client for the calendar feature.