January 24, 2026—KB5078133 (OS Build 25398.2097) Out-of-band

Summary

​​​​This out-of-band update for Windows Server 23H2 (KB5078133) is cumulative. It includes updates from previous security, along with an additional fix. To learn more about differences between security updates, optional non-security preview updates, out-of-band (OOB) updates, and continuous innovation, see Windows monthly updates explained. For information on Windows update terminology, see the different types of Windows software updates.

To view the latest updates about this release, visit the Windows release health dashboard or the update history page for Windows Server 23H2. 

Improvements

This out-of-band (OOB) update includes quality improvements. This update is cumulative and includes security fixes and improvements from the January 13, 2026, security update (KB5073450) and the out-of-band update (KB5077792) from January 17, 2026, in addition to the following:

• [File System] Fixed: After installing the Windows update released on and after January 13, 2026, some applications became unresponsive or encountered unexpected errors when opening files from or saving files to cloud-based storage, such as OneDrive or Dropbox. In certain Outlook configurations that store PST files on OneDrive, Outlook may hang and fail to reopen unless the process is terminated or the system is restarted. Users may also see missing sent Items or previously downloaded emails being re‑downloaded.

If you installed earlier updates, your device downloads and installs only the new updates contained in this package.

Windows Server, version 23H2 servicing stack update (KB5068778) - 25398.1960

This update makes quality improvements to the servicing stack, which is the component that installs Windows updates. Servicing stack updates (SSU) ensure that you have a robust and reliable servicing stack so that your devices can receive and install Microsoft updates. To learn more about SSUs, see Simplifying on-premises deployment of servicing stack updates.

Known issues in this update

How to get this update

Before you install this update

Microsoft now combines the latest servicing stack update (SSU) for your operating system with the latest cumulative update (LCU). For general information about SSUs, see Servicing stack updates and Servicing Stack Updates (SSU): Frequently Asked Questions.

Install this update

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

File Information

For a list of the files provided in this update, download the file information for cumulative update 5078133. 

For a list of the files provided in the servicing stack update, download the file information for the SSU (KB5068778) - version 25398.1960.