April 19, 2026—KB5091573 (OS Build 17763.8647) Out-of-band

Windows Secure Boot certificate expiration

Important: Secure Boot certificates used by most Windows devices are set to expire starting in June 2026. This might affect the ability of certain personal and business devices to boot securely if not updated in time. To avoid disruption, we recommend reviewing the guidance and taking action to update certificates in advance.

For details and preparation steps for Windows devices, see Windows Secure Boot certificate expiration and CA updates.

For details and preparation steps for Windows servers, see the following resources:

Summary

This article lists the fixes and quality improvements included in this out-of-band update.

Applies to: Windows Server 2019

This out-of-band update includes fixes and improvements that are part of the following update:

April 14, 2026—KB5082123 (OS Build 17763.8644)

The following is a summary of the issues that this out-of-band update addresses when you install this update. The bold text within the brackets indicates the item or area of the change we are documenting.

[Domain controllers (known issue)] Fixed: After installing the April 14, 2026, (KB5082123) Windows security update and restarting, domain controllers with multi-domain forests that use Privileged Access Management (PAM), might experience startup issues. In some cases, Local Security Authority Subsystem Service (LSASS) might stop responding, leading to repeated restarts, and preventing authentication and directory services, which can make the domain unavailable.

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

For more information about security vulnerabilities, please refer to the new Security Update Guide website and the April 2026 Security Updates.

For information about Windows update terminology, see the article about the types of Windows updates and the monthly quality update types. For an overview of Windows 10, version 1809, see its update history page.

Known issues in this update

We are currently not aware of any issues with this update.

Servicing stack update (KB5082118) - 17763.8642

Microsoft now combines the latest servicing stack update (SSU) for your operating system with the latest cumulative update (LCU). SSUs improves the reliability of the update process and includes fixes to the servicing stack, the component that installs Windows updates.

Note: This servicing stack update (SSU) includes enhanced logic to verify whether a device is hosted on Azure, leveraging an updated certificate chain for validation. To ensure that the device can access the required certificate update domains to successfully download and install certificate updates, see Certificate downloads and revocation lists and Azure Certificate Authority details. To learn more about SSUs, see Servicing stack updates.

How to get this update

Before you install this update

You must have installed the August 10, 2021, SSU (KB5005112) before installing this out-of-band update.

Install this update

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

Available	Next Step
	This out-of-band update is available only from the Update Catalog.

If you want to remove this update

CAUTION Before you decide to remove this update, please see Understanding the risks: Why you should not uninstall security updates.

To remove the LCU after installing the combined SSU and LCU package, use the DISM/Remove-Package command line option with the LCU package name as the argument. You can find the package name by using this command: DISM /online /get-packages.

Running Windows Update Standalone Installer (wusa.exe) with the /uninstall switch on the combined package will not work because the combined package contains the SSU. You cannot remove the SSU from the system after installation.

File information

A list of the files that are included in this update are provided in a CSV (Comma delimited) (*.csv) file. The file can be opened in a text editor such as Notepad or in Microsoft Excel.

Download Icon Download the file information for this out-of-band update KB5091573.