The WordPress Online Booking and Scheduling Plugin WordPress plugin before 22.5 does not sanitise and escape some of its settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup)
https://wpscan.com/vulnerability/dea6077a-81ee-451f-b049-3749a2252c88