CVE-2026-18121 Concrete CMS 9.5.2 and below is vulnerable to an authorization bypass (IDOR) in the Calendar block's frontend event dialog (/ccm/calendar/view_event/{bID}/{occurrence_id}).

Concrete CMS 9.5.2 and below is vulnerable to an authorization bypass IDOR because the frontend calendar lightbox endpoint /ccm/calendar/viewevent/bID/occurrenceid does not verify that the caller is permitted to view the calendar that owns the requested event occurrence. The controller loads the...