Microsoft Releases Temporary Fix for Domain Login Issues Caused by Security Updates
Microsoft has released a temporary fix for a known issue affecting Windows 11 users who cannot log in with valid domain credentials after installing the September security updates. The problem, which causes domain trust failures and sign-in issues with valid domain credentials, is linked to the Machine Identity Isolation feature enabled by the latest security patches.
Admins have reported that enabling Machine Identity Isolation in enforcement mode and then disabling it breaks domain authentication and requires the device to be unjoined and rejoined to the Windows domain. Microsoft has confirmed that these authentication issues are triggered by the September 2026 security updates, which enable Machine Identity Isolation.
The company has warned admins that this feature is only supported for environments connected to domain controllers running at a Windows Server 2025 Domain Functional Level (DFL) and above. To resolve the issue, admins must disable Machine Identity Isolation on all devices previously configured to use it and not connected to Windows Server 2025 domain controllers.