KB5078129

Microsoft has released cumulative update KB5078129 for Windows 10 version 22H2, available through the Extended Security Updates (ESU) program. This update is intended for systems with x86, x64 (AMD64), and ARM64 processors and resolves a critical issue with application freezes and file operation errors in cloud storage services, including OneDrive and Dropbox, which appeared after the January updates. Specifically, it fixes a crash that caused Outlook to freeze when using PST files stored in OneDrive, as well as issues with duplicate downloading of emails. It is important to note that update KB5078129 is only available for manual installation from the Microsoft Update Catalog.

• File system. Fixes an issue where after installing the updates from January 13, 2026, some applications might become unresponsive or encounter errors when opening and saving files in cloud storage services such as OneDrive or Dropbox.
• Microsoft Outlook. In certain configurations where PST files are stored in OneDrive, the application could freeze and would not restart without force-closing the process or rebooting the system. Users could also experience items disappearing from the Sent folder or duplicate downloading of previously downloaded emails.

Currently, no critical problems specifically related to this update have been reported. However, to continue receiving security updates after the end of support for Windows 10, Microsoft recommends that users enroll in the Extended Security Updates (ESU) program. If you have already installed the previous updates, only the new fixes contained in this package will be downloaded and installed on your device.

Update KB5078129 is not available for installation through Windows Update. You can manually download the update from the Microsoft Update Catalog.

If you wish to perform a clean installation of Windows 10 Build 19045.6812 (version 22H2), you can use the UUP dump service to download UUP files directly from official Microsoft servers and create a bootable ISO image.

How the new features work:

File system: Fixed file locking issues with cloud sync engines. After updates from January 13, 2026, OneDrive/Dropbox clients could hold exclusive file handles after write operations, causing timeouts on subsequent opens. The new CfUpdatePlaceholder mechanism correctly releases locks and notifies the wcifs.sys filter about hydration state changes.

Microsoft Outlook: Fixed freezes when working with PST files in OneDrive. Outlook used memory-mapped I/O, but the cloud sync engine could exclusively lock PST files at the .\C: level. The solution migrates to asynchronous ReadFile/WriteFile calls with the FILE_FLAG_OVERLAPPED flag and adds USN journal change tracking for the Sent folder, preventing duplicate downloads of already fetched emails.

The last 10 Windows updates: