Microsoft Fixes Windows 11 Boot Failure Bug Affecting Commercial Systems

Microsoft has resolved a Windows 11 boot failure issue that caused some commercial systems to display an "UNMOUNTABLE_BOOT_VOLUME" error after installing recent security updates. The fix is delivered in the February 2026 Patch Tuesday update KB5077181, released on February 10, 2026.

The Boot Failure Problem

The boot issue affected a limited number of commercial Windows 11 devices running versions 25H2 and 24H2. According to a private enterprise advisory seen by Susan Bradley of Ask Woody, impacted devices suffered boot failures after installing the January 13, 2026 security update KB5074109 or later updates.

Affected systems displayed a black screen with the message: "Your device ran into a problem and needs a restart. You can restart." At that point, systems were unable to boot and required manual recovery to restore functionality.

Microsoft previously confirmed the issue was caused by the failed installation of the December 2025 security update, leaving devices in an improper state after the installation rolled back. Attempting to install future Windows updates on devices with this "improper state" could cause the system to become unbootable.

The company stated the issue affected only physical devices running Windows 11 25H2 and 24H2, and did not receive reports of it affecting home users or virtual machines.

Microsoft's Resolution Timeline

Microsoft took a phased approach to resolving this critical boot failure issue:

1. Initial Prevention: On January 29, 2026, Microsoft released an optional non-security preview update KB5074105 to help prevent additional systems from becoming affected by the bug.

2. Full Resolution: The issue is now fully resolved in the Windows 11 KB5077181 update released during the February 2026 Patch Tuesday and later updates.

"This issue is fully resolved in the Windows security update released on February 10, 2026 (the Resolved KBs listed above), and later updates," reads Microsoft's advisory.

Impact on Affected Systems

Unfortunately, devices that became unbootable before the fix was released may still require additional remediation. Microsoft advises enterprise customers whose devices remain affected to contact Microsoft Support for Business for assistance restoring system stability.

The selective nature of this advisory raises questions about Microsoft's communication strategy. The company did not share this advisory publicly, as it does for other known Windows issues, limiting the information to enterprise customers through private channels.

Broader Context

This boot failure issue is part of a series of Windows update problems that have affected enterprise customers. Microsoft has been investigating various Windows 11 stability issues throughout 2025 and early 2026, including problems with Chrome launching and security vulnerabilities in Notepad.

For enterprise IT administrators managing Windows 11 deployments, this incident underscores the importance of maintaining robust backup and recovery procedures, particularly when deploying security updates to commercial environments. The fact that the issue was limited to commercial systems suggests specific configurations or deployment methods may have contributed to the problem.

Organizations running Windows 11 25H2 or 24H2 should ensure they have applied the February 2026 Patch Tuesday updates, particularly KB5077181, to prevent potential boot failures and maintain system stability.