Auth bypass in Concrete Cms

CVE-2026-8239

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.

Vulnerability class: Broken Access Control

Published · last modified .

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.003 (23.1th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 23rd percentile — 23.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-8239: held from 0.002 to 0.003.

EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001

Affected products

Weakness classification (CWE)

Public proof-of-concept exploits

References

Frequently asked questions

What is CVE-2026-8239?
CVE-2026-8239 is a medium-severity vulnerability in Concrete Cms, classified under Missing Authorization. CVSS score: 5.3/10. Published 2026-05-21.
How severe is CVE-2026-8239?
Medium severity. CVSS v3 base score is 5.3 out of 10.
Is CVE-2026-8239 known to be exploited?
1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.