Microsoft has shared a temporary workaround for a Windows 11 issue caused by the September 2026 security updates that blocks some users from signing in with valid domain credentials. The problem is tied to Machine Identity Isolation enforcement and can break domain trust on affected enterprise systems, especially outside Windows Server 2025 DFL environments. #Microsoft #Windows11 #MachineIdentityIsolation #KB5124008 #KB5124012
Keypoints
- September 2026 updates triggered domain trust and sign-in failures on some Windows 11 systems.
- The issue is linked to Machine Identity Isolation being honored in enforcement mode.
- The feature is only supported in environments using Windows Server 2025 Domain Functional Level or above.
- Microsoft advises disabling Machine Identity Isolation on unsupported devices and then restarting them.
- Admins may need to reset the secure channel after turning off the feature.