The Easy Appointments WordPress plugin before 3.12.28 does not correctly validate shortcode input in one of its block-rendering actions, checking only the first tag of the supplied string against an allowlist while rendering the entire string, allowing users with contributor-level access to execute arbitrary registered shortcodes.
https://wpscan.com/vulnerability/6e95e74b-89b2-4a4f-b8a8-91d7b76cdcd2/