KB5126657: Windows 10 Version 21H2 Security Update (October 2026)

Full tracking and change history for KB5126657

Released

2026-10-13

Last changed

2026-10-13

Changes tracked

1

Senserva began recording day-to-day change history on 2026-07-07, and refreshes it several times a day. Release dates are historical where Microsoft publishes them; revision history is tracked from that date forward, so it does not include changes made before then.

Check if KB5126657 is installed

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Known issues, from Microsoft

Quoted from Microsoft's support article for KB5126657 (checked 2026-10-13). Verify against the article before acting.

USB Audio Class 1.0 devices with error Code 10 or no output

Symptoms

After installing the September 8, 2026, Windows security update, some USB Audio Class 1.0 devices might fail to start or produce audio. Affected devices might experience one or more of the following symptoms:

The device displays an error in Device Manager: "This device cannot start (Code 10).”

No audio output.

Volume controls are unresponsive or remain at zero.

Sound settings are unresponsive or unavailable.

Some devices might function in standard stereo configurations but fail when using multichannel audio features, including 8-channel or 3D audio modes. Some customers have reported that they're able to restore audio in these cases by switching to 2-channel mode.

This issue is limited to USB Audio Class 1.0 devices.

Resolution

This issue is partially resolved in the out-of-band (OOB) update released on September 14, 2026. This OOB update resolves the symptoms experienced on devices using 8-channel or 3D audio modes. Microsoft is working to address the other symptoms and will provide more information when it is available.

IT administrators who need an immediate workaround for the symptoms not addressed yet by the OOB update should contact Microsoft Support for Business for assistance.

Applies to: Windows 10 Enterprise LTSC 2021 and Windows 10 IoT Enterprise LTSC 2021

Important

Use EKB KB5003791 to update to Windows 10, version 21H2 on supported editions.

This security update includes fixes and quality improvements that are part of the following updates:

September 8, 2026—KB5122878 (OS Builds 19045.7725 and 19044.7725)

Extended Security Updates (ESU) Licensing Preparation Package for Windows 10

September 14, 2026—KB5129236 (OS Builds 19045.7727 and 19044.7727) Out-of-band

The following is a summary of the issues that this update addresses when you install this update. If there are new features, it lists them as well. The bold text within the brackets indicates the item or area of the change we are documenting.

[Time and Date]

This update enables permanent Daylight Savings Time (DST) support for British Columbia and Alberta starting in November 2026.

This update introduces the new time zone Manitoba Standard Time "(UTC-5:00) Manitoba".

[ReFS security] This update adds auditing and optional policy controls for ReFS volumes on externally attached storage devices. Auditing is enabled by default, while enforcement controls remain disabled by default to give administrators time to evaluate and prepare for future security hardening changes. To learn more, see KB5130741 .

[Storage Spaces] ...

CVEs fixed by this update

Sorted exploited-first, then by CVSS. Every CVE links to its Senserva page with the full risk facts, references, and a ready-to-paste AI prompt.