KB5078774 for Windows Server 2012 R2

KB5078774 is the ESU Monthly Rollup Update for Windows Server 2012 R2. It was released on 10 March 2026 under the ‘Patch Tuesday’ program.

Salient points

• KB5078774 supersedes KB5075970 released in Febuary 2026.
• KB5078774 requires a Servicing Stack Update to be installed prior to installing the main monthly rollup update. KB5079233 is the SSU corresponding to KB5078774.
• If you install language pack after installing KB5078774, you would need to reinstall the security update once again. All language pack installations must be completed before installing the monthly rollup update on Windows Server 2012 R2.
• KB5078774 is an Extended Security Update. A valid subscription key to the ESU program is required before installing the monthly rollup update.
• Windows Server 2012 R2 is impacted by 32 security vulnerabilities reported in March 2026 security bulletin.
• No zero-day vulnerabilities affect Windows Server 2012 R2 and Windows Server 2012 R2 Server Core installation.
• No Critical security vulnerabilities affect Windows Server 2012 R2 in the latest March security bulletin.
• KB5078774 corresponds to build 6.3.9600.23074 for Windows Server 2012 R2.
• Meanwhile, the last cumulative update for Internet Explorer on Windows Server 2012 R2 was last released in October 2025 (KB5066840)

Servicing Stack Update KB5079233

The Servicing Stack Update for Windows Server 2012 R2 for March is KB5079233.

For automated deployments of KB5078774 through the Windows Update program, the Servicing Stack Update KB5079233 is offered for installation as part of the installation process of the monthly rollup update KB5078774. No further action is needed to install KB5079233 for automated installations of KB5078774.

WSUS administrators need to authorize or approve KB5079233 before KB5078774 is fetched and installed in WSUS.

If you choose to deploy KB5078774 manually, you need to download and install KB5079233 on the Windows Server 2012 R2.

• Download KB5079233 from the Microsoft Update Catalog page (10.6 MB)

The Servicing Stack Update file is a small file of 10.6 MB. Upon installation, it would not cause server reboot. Once the SSU is installed, you can proceed with the installation of the main monthly rollup update KB5078774.

Download KB5078774

You can download the monthly rollup update KB5078774 for Windows Server 2012 R2 from the Windows Update Catalog page shared below:

• Download KB5078774 from the Microsoft Update Catalog page (564.2 MB)

We would reiterate that you need a valid ESU program subscription before you could install the ESU KB5078774 on Windows Server 2012 R2.

Zero-day Vulnerabilities

No zero-day vulnerability affects Windows Server 2012 R2 and Windows Server 2012 R2 Server Core installation, as per the latest security reported released by Microsoft.

Critical vulnerabilities

No Critical vulnerabilities have been reported for Windows Server 2012 R2 in March 2026.

KB5078774 – Changelog

Since this is an ESU, the focus remains on securing the Windows Server 2012 R2 deployments. The following changes have been reported for KB5078774:

• [Internal Windows OS] Miscellaneous security improvements were made to internal Windows OS functionality.

Internet Explorer Cumulative Update – KB5066840

To secure the Windows Server 2012 R2, you also need to patch Internet Explorer 11 with the latest cumulative update. KB5066840 is the cumulative update for Internet Explorer released on 14 October 2025. No new IE update has been released in November or December 2025.

You can download the IE Cumulative Update for Windows Server 2012 R2 from the link shared below:

Download Cumulative Update for Internet Explorer – KB5066840 (54.9 MB)