Windows 10 KB5126657: October 2026 Security Update Details

Microsoft has released the October 2026 Extended Security Update for Windows 10: KB5126657. This update arrived on October 13, 2026, the very day the first year of the ESU program ends. Here’s what you need to know about it.

This update includes a large number of security fixes, notably because the October 2026 Patch Tuesday addresses more than 1,400 vulnerabilities across Microsoft’s product lineup. September’s record has already been broken, and by a wide margin. After installing this update, Windows 10 22H2 machines move to build 19045.7807, while Windows 10 Enterprise LTSC 2021 systems move to build 19044.7807.

As mentioned in the introduction, this update also marks the end of the first year of the Windows 10 ESU program, which ends on October 13, 2026. To keep receiving fixes until October 12, 2027, organizations must pay for an additional year. Private users can also benefit from one more year (see this article). This Patch Tuesday also spells the end for Windows 10 Enterprise LTSB 2016: October’s update is the last one for this edition.

File History, Secure Boot: what KB5126657 fixes

As expected, Microsoft is not delivering any new features on Windows 10. However, KB5126657 fixes bugs:

• File History: backup and restore to an external drive or network location now works again. I previously published an article about this File History bug introduced by the September 2026 updates. It is now fixed.
• Storage Spaces Direct: some virtual disks could remain offline after an update because valid metadata was treated as invalid during recovery.
• Secure Boot: Microsoft continues the automatic rollout of the new Secure Boot certificates through Windows Update.
• Time zones: daylight saving time becomes permanent for British Columbia and Alberta starting in November 2026, and a new time zone, “(UTC-5:00) Manitoba,” appears.

However, a known issue remains with some USB Audio Class 1.0 devices since the September 2026 updates. The symptoms are as follows: Code 10 error in Device Manager, no sound, or volume controls that no longer respond. The out-of-band update released on September 14, 2026, which also fixed the RDS bug, had already resolved some audio issues, but not all of them. Microsoft says it is still working on a fix.

ReFS on a USB drive: auditing starts, blocking arrives in January 2027

If you use USB drives formatted with ReFS, this is the most notable change. KB5126657 adds audit and control capabilities for ReFS volumes mounted from removable or external storage. This hardening does not apply only to Windows 10: according to KB5130741, it applies to all supported Windows versions, up to Windows Server 2025. "ReFS on removable media, such as a USB drive, is not a supported configuration," Microsoft reminds users.

Microsoft has planned a two-step rollout, and it starts now:

• Since October 13, 2026: auditing is enabled by default, blocking is not. With audit mode, Windows writes a warning to the System log (ID 524, source ReFS), once per volume and per boot.
• With the January 2027 update: auditing and blocking are enabled by default. The affected ReFS volumes will no longer be mounted (unless the admin changes the setting). The RefsRemovableDeviceMountPolicy setting can be modified to adjust the behavior (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem): 0 to disable, 1 for audit (default), and 2 to block.

If you use USB drives formatted with ReFS, for example for backups, now is the time to address it.

The Windows 10 ESU update list

Below is the list of Windows 10 ESU updates published to date.

This article is also an opportunity to note that Microsoft has quietly extended the free ESU program until October 2027 for enrolled consumer devices. Unlike businesses, private users do not need to do anything.

To go further:

• Patch Tuesday - October 2026: 1,407 vulnerabilities fixed, including three zero-days
• Windows 11 - October 2026 Update

Florian Burnel Co-founder of IT-Connect

Systems and network engineer, co-founder of IT-Connect and Microsoft MVP "Cloud and Datacenter Management". I'd like to share my experience and discoveries through my articles. I'm a generalist with a particular interest in Microsoft solutions and scripting. Enjoy your reading.

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