October 13, 2026—KB5126868 (OS Build 14393.9612)

Applies To
Windows Server 2016, all editions Win 10 Ent LTSB 2016 Win 10 IoT Ent LTSB 2016

Important

Free support for Windows 10 Enterprise LTSB 2016 and Windows 10 IoT Enterprise 2016 LTSB ends on October 13, 2026. Free support for Windows Server 2016 ends soon. To learn about continuing support, see Plan for Windows Server 2016 and Windows 10 2016 LTSB end of support.

Summary

This article lists the security issues and quality improvements included in this cumulative security update.

Applies to: Windows Server 2016

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

The following is a summary of the issues that this update addresses. 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.

  • [Distributed Key Manager (DKM)] This update automatically remediates insecure DKM container ACL configurations in AD FS by default. Administrators can opt out of automatic remediation by setting RemediateDkmAcl to 0. This change helps address an elevation of privilege vulnerability that can occur when the DKM container ACL is overly permissive. For more information about how to manage this change, see CVE-2026-56155: AD FS Distributed Key Manager container ACL hardening.

  • [Secure Boot] This update continues the deployment of updated Secure Boot certificates using the latest high-confidence targeting data to identify eligible devices that are ready to automatically receive the new certificates. Deployment through Windows Update remains ongoing across supported device.

  • [Storage Spaces] This update addresses an issue that might cause some Storage Spaces Direct virtual disks to remain offline after installing a Windows update. This issue occurs when valid tiered storage metadata is incorrectly identified as invalid during recovery, preventing affected virtual disks and dependent workloads from coming online.

Note If you installed earlier updates, only the new updates contained in this package will be downloaded and installed on your device.

For information about security vulnerabilities, see the Security Update Guide website and the October 2026 Security Updates.

Known issues in this update

Users might be unable to sign in to OWA or send emails on Exchange Server

Symptoms:

After installing this update, some on-premises Exchange servers might experience issues accessing or sending email. Users might be unable to sign in to Outlook on the web (OWA), or email messages sent from Outlook might remain in the Outbox and not be delivered. Additionally, Exchange might experience issues accessing mailboxes during mailbox replication.

In some affected configurations, Exchange Server OWA might fail with an error MapiExceptionMdbOffline: Unable to make connection to the server. (hr=0x80004005, ec=1142) with Event ID 1006 logged in the application log. Another reported symptom is growing email queues. Installing the October 2026 Exchange server security updates isn’t required for these issues to occur.

Workaround

This issue can be temporarily mitigated by modifying the registry key as described in Exchange servers may become unstable after installation of October 2026 Windows updates.

The October 2026 update introduced a default limit on the amount of memory used by Endpoint Mapper when handling Endpoint Lookup calls.

For workloads such as Exchange Server, the default limit of 512 simultaneous Endpoint Lookup calls might not be sufficient under heavy load. Administrators can use this registry setting to increase the maximum number of simultaneous Endpoint Lookup calls, which increases the amount of memory that Endpoint Mapper can use.

Microsoft Support: An additional mitigation is available for affected devices through Microsoft Support. To apply this mitigation in your organization, please contact Microsoft Support for business.

Next steps: Microsoft investigating this issue and will provide more information when it is available.

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.

How to get this update

Before you install this update

To install updates released on or after January 14, 2025, we recommend that you first install the latest Servicing Stack Update (SSU). If your device or offline image does not have the latest SSU installed, you might not be able to install this update.

Caution

Until you install the SSU, this update might not be offered to your device. To reduce your security risk, install the SSU as soon as possible.

  • If you use Windows Update, the latest SSU (KB5126649) will be offered to you automatically. If the latest SSU is not installed, you might not be able to install this update.
  • If you use Windows Update for Business, the latest SSU (KB5126649) will be offered to you automatically. If the latest SSU is not installed, you might not be able to install this update.
  • If you use the Update Catalog, we recommend that you download and install the latest SSU (KB5126649). If the latest SSU is not installed, you might not be able to install this update.
  • If you are a Windows Server Update Services (WSUS) administrator, you must approve SSU KB5126649 and this update KB5126868. For general information about SSUs, see Servicing stack updates.

Get and install this update

To get and install this update, use one of the following Windows and Microsoft release channels.

Available Next step
Available This update will be downloaded and installed automatically from Windows Update.

File information

A list of the files included in this update is provided in a CSV (Comma delimited) (*.csv) file. You can open the file in a text editor such as Notepad or in Microsoft Excel.

Note The English (United States) version of this software update might contain files for additional languages.

Download Download the file information for cumulative update KB5126868.

References

  • Microsoft Store application updates

    Windows updates do not install Microsoft Store application updates. Enterprise users should see Microsoft Store apps - Configuration Manager. Consumer users should see Get updates for apps and games in Microsoft Store.

  • Secure Boot certificate updates remain in progress as Microsoft transitions devices from certificates that began expiring in 2026 to newer certificates. Devices that have not yet received the newer certificates can continue to start and receive standard Windows updates. Microsoft will continue delivering the newer Secure Boot certificates to eligible devices through Windows Update.

Change log
Change date Change description
October 14, 2026 Added a release note: "[Storage Spaces] This update addresses an issue that might cause some Storage Spaces Direct virtual disks to remain offline after installing a Windows update. This issue occurs when valid tiered storage metadata is incorrectly identified as invalid during recovery, preventing affected virtual disks and dependent workloads from coming online."