XWiki Full Calendar Macro displays objects from the wiki on the calendar. Prior to version 2.4.5, users with the right to view the Calendar.JSONService page (including guest users) can exploit a SQL injection vulnerability by accessing database info or starting a DoS attack. This issue has been patched in version 2.4.5.
https://github.com/xwiki-contrib/macro-fullcalendar/security/advisories/GHSA-2g22-wg49-fgv5
https://github.com/xwiki-contrib/macro-fullcalendar/commit/5fdcf06a05015786492fda69b4d9dea5460cc994