Microsoft Issues Workaround for Windows 11 Domain Login Failures After September 2026 Updates

On September 17, 2026, Microsoft shared a temporary fix for a known issue impacting Windows 11 systems. The problem prevents users from logging in with valid domain credentials after installing the September 2026 security updates. The bug affects devices joined to Active Directory domains and appears to have been introduced by the cumulative security update. Microsoft has not released a permanent patch at this time, instead providing a temporary workaround to restore authentication functionality. The company has stated that no evidence of exploitation in the wild has been found, and the issue is treated as a bug rather than a security vulnerability. Microsoft advisories and support documentation detail the steps required to implement the workaround, which involves modifying specific registry keys or group policy settings. Affected organizations are advised to apply the workaround promptly to avoid productivity loss and user lockouts. A permanent update is expected in a future release, though Microsoft has not provided a specific timeline.