Windows 11 Devices Facing Boot Issues After January 2026 Security Update

Microsoft is currently looking into reports of Windows 11 devices encountering boot failures with “UNMOUNTABLE_BOOT_VOLUME” errors following the installation of the January 2026 Patch Tuesday security updates.

The problem specifically affects Windows 11 version 25H2 and all editions of Windows 11 version 24H2 after users install the KB5074109 cumulative update that was part of this month’s updates.

Users have reported that their systems are failing to start and are displaying stop errors during the boot process.

Microsoft has acknowledged the issue, stating that a limited number of devices are experiencing boot failures with the stop code ‘UNMOUNTABLE_BOOT_VOLUME’ after installing the January 2026 Windows security update released on January 13, 2026, and subsequent updates.

Affected devices are showing a black Windows crash screen with a message prompting a restart, indicating that manual recovery efforts are needed to boot the systems.

It is important to note that only physical devices have been impacted by this bug, with no virtual machines reported to be affected.

Microsoft is actively seeking feedback from affected users and administrators through the Feedback Hub app to investigate whether this behavior is connected to a Windows update.

The company has reassured users that they are investigating the issue and will provide updates once more information is confirmed.

In addition to addressing the boot issue, Microsoft has released emergency out-of-band updates to resolve an issue causing Microsoft Outlook to freeze when PST files are stored in cloud services like OneDrive or Dropbox.

This problem primarily affects the Outlook class, commonly used in enterprise environments.

Addressing Security Concerns

Whether you’re managing old keys or securing AI-generated code, this guide assists your team in building securely from the outset.

Download the cheat sheet to simplify secrets management and enhance security.

Download Now