CVE-2026-81905 Concrete CMS CVE debrief

Who should care

Defenders responsible for Concrete CMS installations, security teams, and administrators should assess exposure and implement mitigations to prevent potential hash redemption attacks.

Why it matters

The vulnerability in Concrete CMS allows an attacker to redeem a hash issued for one purpose for another purpose, amplifying the impact of any hash disclosure. Defenders should prioritize verifying inventory, monitoring for potential hash disclosure, and implementing compensating controls to mitigate the impact of hash redemption.

• An attacker can use a long-lived registration hash to set a new password on the target account
• An attacker can use a password-reset hash to activate an account
• Defenders need to verify inventory and monitor for potential hash disclosure
• Defenders need to implement compensating controls to mitigate the impact of hash redemption

Technical summary

The vulnerability in Concrete CMS allows an attacker to redeem a hash issued for one purpose for another purpose due to the redemption path resolving a hash by value alone without verifying its type. This issue requires the attacker to first obtain a valid hash through a separate channel, such as email interception or log exposure. The attacker can then use a long-lived registration hash to set a new password on the target account or use a password-reset hash to activate an account. Defenders should prioritize verifying inventory, monitoring for potential hash disclosure, and implementing compensating controls to mitigate the impact of hash redemption.

Defensive priority

Defenders should prioritize verifying inventory and monitoring for potential hash disclosure, assessing exposure, and implementing compensating controls to mitigate the impact of hash redemption.

Recommended defensive actions

• Verify inventory of Concrete CMS installations and assess exposure to potential hash disclosure
• Monitor logs and email for potential hash leakage
• Implement compensating controls to mitigate the impact of hash redemption
• Consider upgrading to Concrete CMS version 9.5.3 or later
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and NVD vulnerability detail page provide information on the vulnerability, including its CVSS v4.0 score of 6.3 and vector CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/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.