Microsoft Out-of-Band Update KB5078127 Fixes Windows 11 Cloud File Access and Outlook PST Freezes
Microsoft released a second January out-of-band Windows update, KB5078127, to remediate issues introduced by the January Patch Tuesday security update (KB5074109) that disrupted cloud-backed workflows on Windows 11. Reported impacts included applications being unable to open or save files to cloud storage providers such as OneDrive and Dropbox, with a common enterprise failure mode involving Outlook hanging when PST files were stored on OneDrive; users often had to terminate processes or reboot to recover.
KB5078127 is a cumulative OOB release that rolls up prior January fixes, including the earlier out-of-band update (KB5077744) and the security/quality improvements from KB5074109, and it also includes a bundled Servicing Stack Update (KB5071142) intended to improve update reliability. The update is available via Windows Update and the Microsoft Update Catalog; organizations with automatic updates enabled should receive it automatically, while IT teams can expedite deployment through standard Windows update management workflows.
Timeline
Jan 26, 2026
Microsoft releases emergency update KB5078127 for file system and Outlook freezes
On January 26, 2026, Microsoft released out-of-band cumulative update KB5078127 to fix file system compatibility bugs introduced by KB5074109. The update addressed application freezes, cloud storage failures involving OneDrive and Dropbox, and Outlook hangs when PST files were stored on OneDrive, while also including prior January security and quality fixes.
Jan 26, 2026
Microsoft investigates Windows boot failures tied to January updates
By January 26, 2026, Microsoft was investigating another issue linked to the January Windows updates that could leave some Windows 11 24H2 and 25H2 systems unable to boot, showing a black screen and an UNMOUNTABLE_BOOT_VOLUME stop code. Affected devices could require manual recovery through Windows Recovery.
Jan 17, 2026
Microsoft releases OOB update KB5077744 for cloud PC remote connection issues
On January 17, 2026, Microsoft issued an out-of-band update, KB5077744, to address problems with remote connections to Windows Cloud devices and Secure Launch. This fix was later bundled into a subsequent emergency update.
Jan 13, 2026
Microsoft ships January Patch Tuesday update KB5074109
On January 13, 2026, Microsoft released security update KB5074109 for Windows 11. The update later proved to introduce file system compatibility problems affecting cloud storage workflows and Outlook PST files stored on OneDrive.
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