CVE-2026-81912 Concrete CMS CVE debrief

Who should care

Concrete CMS administrators and users with group management privileges should assess their exposure and apply necessary patches. Defenders should care about CVE-2026-81912 because it allows for Cross-Site Request Forgery in Concrete CMS, potentially leading to unauthorized changes in group permissions and affecting effective authorization. They should verify their Concrete CMS version, review and update group permissions, and monitor for suspicious group  

Why it matters

Defenders should care about CVE-2026-81912 because it allows for Cross-Site Request Forgery in Concrete CMS, potentially leading to unauthorized changes in group permissions and affecting effective authorization. Concrete CMS administrators and users with group management privileges should assess their exposure, verify their version, and apply necessary patches.

• Potential unauthorized changes to group permissions
• Risk of privilege escalation for group members
• Need for verification of Concrete CMS version and patch application
• Possible impact on effective authorization settings

Technical summary

The vulnerability exists in the Move Multiple Groups feature of Concrete CMS before version 9.5.3. An attacker could exploit this by tricking an authenticated user into performing unintended actions, potentially altering group permissions. The vulnerability allows for Cross-Site Request Forgery attacks, which could lead to unauthorized changes in group permissions and affect effective authorization. The CVSS v4.0 score of 5.7 indicates a medium severity vulnerability. Defenders should prioritize verifying their Concrete CMS version and applying the necessary patches to prevent potential unauthorized group changes.

Defensive priority

Defenders should prioritize verifying their Concrete CMS version and applying the necessary patches to prevent potential unauthorized group changes.

Recommended defensive actions

• Verify Concrete CMS version and apply patches
• Review and update group permissions
• Monitor for suspicious group changes
• 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 riodrwn and given a CVSS v4.0 score of 5.7. The affected endpoint is dashboard/users/groups/bulkupdate/confirm(). The vulnerability exists due to the lack of validation for an action token in the Move Multiple Groups feature, allowing for Cross-Site Request Forgery attacks. Defenders should verify their Concrete CMS version and apply patches to prevent potential unauthorized group changes.

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.