KB5078132

Microsoft released an out-of-band cumulative update KB5078132 for Windows 11 version 23H2 (2023 Update). This release addresses a critical issue causing application freezes and file operation errors in cloud storage services, including OneDrive and Dropbox. The package is intended for x64 and ARM64 systems running Enterprise and Education editions, fixes a crash that could cause Outlook to hang when using PST files in OneDrive, and includes all security fixes from previous January updates.

• File system and cloud storage. Fixed an issue where after installing Windows updates released starting January 13, 2026, some applications might stop responding or throw unexpected errors when opening or saving files in cloud locations such as OneDrive or Dropbox.
• Outlook and PST files in OneDrive. In configurations where PST data files were stored in OneDrive, Outlook could freeze and fail to restart without terminating the process or rebooting the system. Users might also experience missing sent emails or re-downloading previously received messages.

No known issues have been reported for this update at the time of release. However, given that it is an out-of-band fix for previous January updates (KB5073455 from January 13 and KB5077797 from January 17), it is recommended to monitor official Microsoft sources for possible regressions. If you already have earlier updates installed, this cumulative update will download and install only the new fixes without reinstalling the previous ones.

Update KB5078132 is distributed through Windows Update for devices running Windows 11 that already have updates KB5073455 or KB5077797 installed. To install it, open Settings > Windows Update and click Check for updates. KB5078132 is also available for manual download from the Microsoft Update Catalog.

How the new features work:

File system and cloud storage: Fixed an issue where after installing Windows updates released starting January 13, 2026, some applications might stop responding or throw unexpected errors when opening or saving files in cloud locations such as OneDrive or Dropbox. Technically, the bug resided in the minifilter driver (cloudflt.sys) during asynchronous IRP_MJ_READ/WRITE processing. A lock in the IRP queue caused timeout (typically 30 seconds) and application crash. The patch corrected synchronization between WOF (Windows Overlay Filter) and the cloud sync provider.

Outlook and PST files in OneDrive: In configurations where PST data files were stored in OneDrive, Outlook could freeze and fail to restart without terminating the process or rebooting the system. Users might also experience missing sent emails or re-downloading previously received messages. The issue was caused by improper Mutex lock contention between Outlook process and OneDrive agent (FileCoAuth.exe) inside unistore.dll. OneDrive locked the PST file for replication while Outlook held the folder content table cache. The patch fixed the LockFileEx call sequence and disabled shadow sync for PST extensions.

The last 10 Windows updates: