Windows bugs and fixes September 22 2026: status

Why are valid domain credentials being rejected?

The domain-login fix has not shipped, BleepingComputer reported on September 17, 2026.

BleepingComputer reported on September 17, 2026, that KB5124008 for Windows 11 24H2 and 25H2 and KB5124012 for Windows 11 26H1 make Windows honor existing or policy-provisioned Machine Identity Isolation enforcement settings.

The Register reported on September 17, 2026, that affected Credential Guard-protected machine accounts can lose their secure channel with an on-premises Active Directory domain, rejecting valid domain credentials.

The entry joined Microsoft’s Windows known issues on September 16, according to The Register on September 17, 2026, and applies when domain controllers do not meet the Windows Server 2025 Domain Functional Level.

BleepingComputer reported on September 17, 2026, that administrators must disable Machine Identity Isolation through the method that enabled it, while The Register said a restart and Test-ComputerSecureChannel repair follow.

The workaround costs a restart, administrative work and the loss of Machine Identity Isolation enforcement, while BleepingComputer warned on September 17, 2026, that disabling enforcement can require unjoining and rejoining the device.

Which emergency Windows updates have shipped?

KB5129195 and KB5129194 have shipped, Neoteo reported on September 16, 2026.

Finance Biggo reported on September 16, 2026, that Microsoft began distributing the cumulative out-of-band updates on September 14 after the September 8 monthly security update.

Finance Biggo reported on September 16, 2026, that KB5129195 serves Windows 11 24H2 and 25H2, KB5129242 serves 23H2, and KB5129194 serves 26H1.

The Windows update fix resolves Remote Desktop connection instability and Hyper-V Plan9 folder-sharing failures, according to Finance Biggo on September 16, 2026, while Neoteo also lists configuration hangs and inaccessible host folders.

My September 15, 2026 report on KB5129195 records the same division between repaired Remote Desktop failures and USB audio symptoms that remained open.

Neoteo reported on September 16, 2026, that Microsoft distributes KB5129195 through Windows Update, Windows Update for Business, Windows Server Update Services and the Microsoft Update Catalog.

What remains broken after the emergency update?

USB audio and Radeon failures remain unresolved, TweakTown reported on September 15, 2026.

TweakTown reported on September 15, 2026, that KB5129195 does not fix reported Radeon driver timeouts, black screens, disappearing displays or system freezes, and Microsoft had not acknowledged those reports as a known issue.

PCMag reported on September 16, 2026, that KB5129195 repairs multichannel USB audio failures involving 8-channel or 3D audio modes but does not repair devices producing no sound.

Neoteo reported on September 16, 2026, that remaining USB audio symptoms were still under investigation, so installing KB5129195 cannot guarantee a complete audio repair.

TweakTown also reported on September 15, 2026, that Explorer.exe crashes and File History failures involving external drives remained open, with no fix listed in KB5129195.

I cannot name a shipped repair or official workaround for the Radeon, no-sound, Explorer.exe or File History faults because TweakTown and PCMag published none on their respective publication dates.

Did Microsoft fix the false Defender warning?

Microsoft's Defender update fixed the false antivirus warning, TechPowerUp reported on September 19, 2026.

TechPowerUp reported on September 19, 2026, that Windows Security had incorrectly claimed Microsoft Defender Antivirus was turned off even when the Windows Security home tab showed protection as active.

Microsoft acknowledged the fault on August 28 and released Microsoft's Defender update on September 17, according to TechPowerUp on September 19, 2026, without identifying one responsible update or rollback KB.

TechPowerUp reported on September 19, 2026, that no manual action is required because the Defender update should arrive automatically unless mandatory security updates are blocked through Group Policy or Registry Editor.

My September 18, 2026 report on Microsoft's Defender update explains the resolved warning separately from the domain-login and emergency-update faults covered today.

TechPowerUp reported on September 19, 2026, that the false alert could appear during startup or return at random, even when notifications had been turned off.

What can a Windows user do today?

Install the package that matches your Windows version, Neoteo advised on September 16, 2026.

For Windows 11 24H2 or 25H2, I would check Windows Update for KB5129195; for Windows 11 26H1, I would check for KB5129194, following Neoteo’s September 16, 2026 version mapping.

For a domain-joined computer rejecting valid credentials, I would have an administrator disable Machine Identity Isolation through its original management method, restart, and repair the secure channel with Test-ComputerSecureChannel, following The Register’s September 17, 2026 instructions.

I would not treat KB5129195 as a complete USB audio repair because PCMag reported on September 16, 2026, that no-sound failures remain, while TweakTown reported on September 15, 2026, that Radeon failures received no fix.

For a false Defender warning, I would allow Microsoft's Defender update to install automatically rather than search for a rollback KB, following TechPowerUp’s September 19, 2026 report.