| Important The installation of this Extended Security Update (ESU) might fail when you try to install it on an Azure Arc-enabled device that is running Windows Server 2012 R2. For a successful installation, please make sure all Subset of endpoints for ESU only are met as described in Connected Machine agent network requirements. |
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Windows Secure Boot certificate expiration
Important: Secure Boot certificates used by most Windows devices have started expiring 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, see Windows Secure Boot certificate expiration and CA updates.
End of support information
Windows Server 2012 R2 reached the end of support (EOS) on October 10, 2023.
Extended Security Updates (ESUs) are available for purchase and will continue for three years, renewable on an annual basis, until the final date on October 13, 2026. For information about the procedure to continue receiving security updates, see KB5031043.
We recommend that you upgrade to a later version of Windows Server. For more information, see Overview of Windows Server upgrades.
Summary
Learn more about this cumulative security update, including improvements, any known issues, and how to get the update.
Windows Server 2012 R2
This security update includes fixes and quality improvements that are 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.
- [Apps (Known issue)] Fixed: This update addresses an issue that affects certain third-party apps that use OLE Automation to interact with Microsoft Office. After installing the June 2026 security update KB5093998, these apps might fail to launch Office or open documents.
- [Distributed Key Manager (DKM)] This update introduces automatic detection of insecure DKM container ACL configurations in AD FS and provides an opt-in remediation mechanism to help administrators strengthen DKM container permissions. For more information about how to manage this change, see CVE-2026-56155: AD FS Distributed Key Manager container ACL hardening.
- [File Explorer (known issue)] Fixed: An issue where the OneDrive shortcut in File Explorer stops working when File Explorer is run with administrative mode.
- [Networking] This update introduces a security hardening change that enforces TDI transport registration requirements. As a result, applications that use sockets over unregistered third-party TDI transports might stop working after installing this update. Registered TDI transports are not affected. For more information, see Third-party TDI transports might stop working after installing Windows security updates released on or after July 14, 2026.
- [Recycle Bin (known issue)] Fixed: This update addresses an issue where the confirmation dialog might display an internal Recycle Bin file name instead of the original file name when permanently deleting a file. This issue might occur after installing the June 2026 security update KB5094041.
- [Remote Desktop (RDP) Security] Support for SHA-2 certificate thumbprints has been added for trusted RDP publishers, with SHA-1 support retained only for backward compatibility and planned for future removal. New guidance is available for managing RDP file security through Group to help organizations reduce phishing risks by controlling which .rdp files users can open. We recommend IT administrators migrate to SHA-256 thumbprints or a stronger algorithm as soon as possible to avoid disruption.
For more information about the resolved security vulnerabilities, please refer to the Deployments | Security Update Guide and the July 2026 Security Updates.
For information about the various types of Windows updates, such as critical, security, driver, service packs, and so on, see Description of the standard terminology that is used to describe Microsoft software updates.
To view other notes and messages, see the Windows 8.1 and Windows Server 2012 R2 update history home page.
Known issues in this update
We are currently not aware of any issues with this update.
How to get this update
Before installing this update
To install any Windows Server 2012 R2 Monthly Rollup released on or after January 14, 2025, we recommend 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 latest SSU, this update might not be offered to your device. To reduce your security risk, install the latest SSU as soon as possible.
- If you use Windows Update, the latest SSU KB5106412 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 you download and install the latest SSU KB5106412. 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 KB5106412 and this update KB5099444.
Deployment
If you deploy dynamic updates such as this update to an existing Windows image, ensure the boot.stl file is included as part of the installation media. Failure to include the file may prevent devices from successfully starting from the installation media and can result in error code 0xc0430001.
Note
The boot.stl file is used during Secure Boot validation and must match the Windows version and architecture of the image you are updating.
To ensure the boot.stl file is included as part of the installation media, do one of the following:
- Use the Update WinPE script to update an existing Windows image. (Recommended)
- Manually copy the boot.stl file from the devices Windows\Boot\EFI folder to the corresponding folder on your installation media before deploying the update.
For general information about SSUs, see Servicing stack updates and Servicing Stack Updates (SSU): Frequently Asked Questions.
Language packs
If you install a language pack after you install this update, you must reinstall this update. Therefore, we recommend that you install any language packs that you need before you install this update. For more information, see Learn about adding a language pack to Windows.
Install this update
To install this update, use one of the following release channels.
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This update will be downloaded and installed automatically from Windows Update. |
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 the file information for cumulative update KB5099444 now.