Hi.Events through 1.9.0 public check-in list endpoints use short_id as sole access control, allowing unauthenticated access to retrieve full attendee lists including emails and personal information. Attackers with knowledge of the short_id can call GET /api/public/check-in-lists/{short_id}/attendees to read attendee data and create or delete check-in records without authentication.
Exploitability
AV:NAC:HAT:NPR:NUI:NVulnerable System
VC:HVI:LVA:NSubsequent System
SC:NSI:NSA:N8.3/CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:NOther