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.
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
End of support
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: Procedure to continue receiving security updates after extended support has ended on October 10, 2023.
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 out-of-band update, including improvements, any known issues, and how to get the update.
Windows Server 2012 R2
This out-of-band update includes fixes and 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.
[Remote Desktop Services (known issue)] Fixed: This update addresses an issue affecting Remote Desktop Services (RDS) after installing the September 2026 Windows security update (KB5123066). In affected environments, RDS might become unstable, causing RDP connection and sign-in failures or servers to become unresponsive during Remote Desktop configuration. Related tools, including Microsoft Management Console (MMC), RDS Licensing Diagnoser, File Explorer, and the Windows Update page, might also stop responding.
[8-channel or 3D audio modes] Fixed: Some USB Audio Class 1.0 devices functioning as expected in standard stereo configurations failed when using multichannel audio features, including 8-channel or 3D audio modes. (Note: There are other audio symptoms not resolved in this OOB update. See the “Known issues in this update” section for more information.)
For more information about the resolved security vulnerabilities, please refer to the Deployments | Security Update Guide and the September 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
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. This issue is limited to USB Audio Class 1.0 devices.
Resolution
Microsoft is working on a resolution and will update this documentation when more information is available.
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 KB5123499 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 KB5123499. 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 KB5123499 and this update KB5123066.
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.
| Available | Next step |
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This update is only available from the Update Catalog. |
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 out-of-band update KB5129243 now.