90-Day Reminder: AD FS DKM container ACL hardening begins in October 2026

Windows updates released in October 2026 will begin Enforcement mode for AD FS Distributed Key Manager (DKM) container ACL hardening. This change is designed to address the elevation of privilege vulnerability documented in CVE-2026-56155 by automatically remediating insecure DKM container ACL configurations on supported Windows Server versions. Organizations using Active Directory Federation Services (AD FS) should use the current Audit mode period to review DKM container permissions and identify potential compatibility issues before enforcement begins. Rollout schedule Enforcement mode begins with the October 2026 Windows security update. Impact on your organization Organizations using AD FS might experience changes to DKM container permissions when remediation is applied during Enforcement mode. Starting with the October 2026 update, remediation will run by default on supported Windows Server versions unless administrators explicitly opt out. Windows Server 2012 and Windows Server 2012 R2 require manual remediation and are not automatically remediated. Action required/recommendations Organizations using AD FS should: Install the July 2026 Windows security update or a later Windows update on AD FS servers. Review AD FS Admin event logs for Event ID 1132, which indicates that DKM container permissions require attention. Review and test remediation during the current Audit mode phase before Enforcement mode begins in October 2026. Review the guidance in: CVE-2026-56155: AD FS Distributed Key Manager container ACL hardening. Compliance considerations No compliance considerations are identified. Review as appropriate for your organization. Message ID: MC1442510

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