Microsoft issues second emergency Windows patch to fix cloud file bug

Microsoft has released a second out-of-band emergency Windows patch this month, KB5078127, to fix a problem that prevented Outlook and other apps from opening or saving files to cloud storage services such as OneDrive and Dropbox. The KB5078127 update also includes the first out-of-band patch issued on Jan.

17 to address remote connections to Windows Cloud devices and Secure Launch, and it carries the security fixes and improvements from the Jan. 13 update. ZDNET's author said they spotted the KB5078127 update on a Windows 11 PC; users can check Settings > Windows Update (or click the button to check for updates), install the patch and then reboot.

At the same time, another glitch caused by the January update is preventing a limited number of Windows 11 25H2 and 24H2 devices from booting. The bug can trigger a black screen at startup and a stop code pointing to an unmountable boot volume, leaving affected machines unable to complete startup and possibly requiring Windows Recovery.

Microsoft said in a support note: "Microsoft has received a limited number of reports of an issue in which devices are failing to boot with stop code 'UNMOUNTABLE_BOOT_VOLUME' after installing the January 2026 Windows security update released January 13, 2026, and later updates. Affected devices show a black screen with the message 'Your device ran into a problem and needs a restart.

Key Topics

Tech, Microsoft, Onedrive, Outlook, Unmountable_boot_volume