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Windows Server 2025 Windows Server 2025 Out-of-band update
Out-of-band

KB5078135

KB5078135: Cumulative update for Windows Server, version 2025, January 2026. Cloud-file errors and Outlook hangs fixed; WSUS details remain missing

In short

Fixes errors opening or saving cloud-based files, including Outlook hangs in some OneDrive PST configurations. WSUS synchronization error details remain unavailable.

Does it affect you? Applies to: Devices running Windows Server 2025. The update package listed is for x64.

Build
26100.32236
Restart
Required

What changes

Fix 1 change

File System

  • Some applications can open files from and save files to cloud-based storage without the unresponsiveness or unexpected errors caused by updates released from January 13, 2026 onward. In some OneDrive configurations, Outlook no longer hangs when working with PST files.1
    The issue affected some Outlook configurations that store PST files on OneDrive; Outlook could fail to reopen unless its process was terminated or the system restarted. Users could also see missing sent items or previously downloaded emails being downloaded again.

Improvement 1 change

Servicing stack

  • The component that installs Windows updates receives quality improvements.2
    The cumulative update includes the Windows Server 2025 servicing stack update KB5072725, build 26100.32131.

Known issues

  1. Open Affects: Organizations and IT administrators

    Windows Server Update Services (WSUS) does not display error details

    After KB5070881 or a later update, WSUS does not display synchronization error details in its error reporting. This functionality is temporarily removed to address a Remote Code Execution vulnerability.3

    Workaround status No workaround yet

    Microsoft has not published a manual workaround for this issue yet. Monitor release health until a resolving update is available.

Technical details

Data sheet · Security · Downloads · Components Click to collapse or expand

Data sheet

Released
2026-01-24
Classification
Updates
Type
Cumulative update
Restart
Required
Replaces
KB5077793, KB5073379, KB5072033, KB5072359
+19 earlier KB5068861, KB5070881, KB5070773, KB5066835, KB5068221, KB5065426, KB5063878, KB5064489, KB5062553, KB5060842, KB5058411, KB5055523, KB5053598, KB5051987, KB5050009, KB5048667, KB5046617, KB5044284, KB5043080
Replaced by
KB5075899
VersionBuildChannel
2025 26100.32236 General availability

Security

No vulnerabilities are listed for this update.

Updated components

137 files changed since the previous update for the same versions.

Top changed componentsFiles
Hyper-V and virtualization2
Kernel2
Audio1
Graphics and display1
Secure Boot1
Settings1
Windows Update1

Sources

Updated
Cited passages from Microsoft's official notes (3)
  1. 1. some applications became unresponsive or encountered unexpected errors when opening files from or saving files to cloud-based storage, such as OneDrive or Dropbox. support.microsoft.com
  2. 2. Microsoft now combines the latest servicing stack update (SSU) for your operating system with the latest cumulative update (LCU). support.microsoft.com
  3. 3. After installing KB5070881 or later updates, Windows Server Update Services (WSUS) does not display synchronization error details within its error reporting. support.microsoft.com
Checked automatically: 8 of 8 checks passed, 3 quoted passages · compared with Microsoft's page on Sep 25, 2026
  • Quotes found in the official pages: passed
  • Numbers found in the sources: passed
  • Vulnerabilities from the dossier only: passed
  • Links to allowed domains only: passed
  • Every official change covered: passed
  • Readable plain text: passed
  • Changes confirmed by the file list: passed
  • Sources agree: passed

A second AI read the text against the sources: correctness 4/5, clarity 4/5, completeness 5/5. How we work

Published by The Update Bureau. Written with AI from Microsoft's own documents, checked by rules and a second AI. How we work · Report a mistake