CVE-2026-8239: Concretecms Concrete CMS

Medium severity, CVSS 5.3. EPSS: 0.3% chance of exploitation in the next 30 days.

Concrete CMS 9.5.0 and below is vulnerable to IDOR. The '/ccm/frontend/conversations/get_rating' endpoint confirms existence and returns rating score for any message by ID. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 6.3 with Vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks Tristan Madani for reporting.

Affected products

• Concretecms Concrete CMS: before 9.5.1 (fixed in 9.5.1)

Published 2026-05-21. Last modified 2026-07-23.