CVE-2026-81901 Concrete CMS CVE debrief

Who should care

Defenders responsible for Concrete CMS installations, particularly those with user content-editing rights, should assess exposure and prioritize verification and remediation. This includes reviewing user permissions, monitoring for suspicious activity, and ensuring that content-editing rights are restricted to trusted users. Additionally, defenders should verify and update Concrete CMS versions to 9.5.3 or later to prevent exploitation of this and similar

Why it matters

Defenders should prioritize verifying and updating Concrete CMS versions to 9.5.3 or later, restricting content-editing rights to trusted users, and monitoring for suspicious activity.

• Users with content-editing rights can alter page properties, template, and type, potentially leading to unauthorized changes.
• The ability to persist JavaScript in the head element of every page can lead to XSS attacks on visitors, including higher-privileged reviewers.

Technical summary

The REST API page update endpoint (PUT /ccm/api/1.0/pages/{cID}) in Concrete CMS 9.2.0 through 9.5.2 did not enforce page-property, page-template, or page-type authorization, allowing users with content-editing rights to alter page properties, template, and type, and persist JavaScript in the head element of every page. This could lead to unauthorized changes and potential XSS attacks on visitors, including higher-privileged reviewers. The vulnerability has a CVSS v4.0 score of 7.2, indicating a high severity level.

Defensive priority

Defenders should prioritize verifying and updating Concrete CMS versions to 9.5.3 or later, and restrict content-editing rights to trusted users.

Recommended defensive actions

• Verify and update Concrete CMS versions to 9.5.3 or later
• Restrict content-editing rights to trusted users
• Monitor for suspicious activity on pages with content-editing rights
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD vulnerability detail provide information on the vulnerability, its CVSS score, and affected versions. The vulnerability was reported by Yonatan Drori from Tenzai. The CVE record was published on 2026-09-14T21:17:26.123Z and has not been modified since then. The NVD detail page provides additional information on the vulnerability, including its CVSS v4.0 score of 7.2 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.