CVE-2026-81918 Concrete CMS CVE debrief

Who should care

Concrete CMS administrators, security teams, and developers responsible for maintaining and securing Concrete CMS installations. Concrete CMS administrators and security teams should prioritize updating to version 9.5.3 or later, reviewing user permissions, and monitoring for suspicious activity on pages with the Page Attribute Display block.

Why it matters

This vulnerability requires attention from Concrete CMS administrators and security teams due to the potential for malicious payload execution. It is crucial to update to version 9.5.3 or later, review user permissions, and monitor for suspicious activity.

• Potential for malicious payload execution in visitor browsers
• Required verification of Concrete CMS version and user permissions
• Need for monitoring and incident response planning

Technical summary

The vulnerability exists in the Page Attribute Display block of Concrete CMS, allowing an authenticated user with edit_page_contents permissions to store a payload that executes in the browser of any visitor who views a page where the block is configured to display a date-type attribute. The vulnerability requires attention from Concrete CMS administrators and security teams due to the potential for malicious payload execution. It is crucial to update to version 9.5.3 or later, review user permissions, and monitor for suspicious activity.

Defensive priority

Medium priority for Concrete CMS administrators and security teams

Recommended defensive actions

• Update Concrete CMS to version 9.5.3 or later
• Review and limit user permissions for edit_page_contents
• Monitor for suspicious activity on pages with the Page Attribute Display block
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• 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

Evidence notes

The vulnerability was reported by Oriol Ortiz and assigned a CVSS v4.0 score of 4.8 by the Concrete CMS security team. The NVD entry is currently Analyzed. The vulnerability requires attention from Concrete CMS administrators and security teams due to the potential for malicious payload execution in visitor browsers. It is crucial to update to version 9.5.3 or later, review user permissions, and monitor for suspicious activity on pages with the Page Attribute Display block.

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.