Microsoft has resolved a Windows 11 issue that caused certain commercial systems to fail during startup with an error message reading UNMOUNTABLE BOOT VOLUME. The fix was delivered as part of the February 2026 Patch Tuesday security release, with the Windows 11 KB5077181 update addressing a problem tied to earlier update installations.
The issue affected a limited number of commercial devices running Windows 11 versions 25H2 and 24H2. Impacted systems experienced boot failures after installing the January 13, 2026, security update KB5074109 or later cumulative updates.
Boot Failures Linked To Earlier Update Rollbacks
According to Microsoft, the problem stemmed from a failed installation of the December 2025 security update. In some cases, when the December update did not install correctly and rolled back, devices were left in what the company described as an improper state. Systems in this condition became vulnerable to startup failures when subsequent updates were applied.
After installing the affected updates, some devices displayed a black screen with a message stating that the device had run into a problem and needed a restart. Attempts to restart did not resolve the issue. Systems were unable to boot and required manual recovery procedures to restore functionality before the release of the Windows 11 KB5077181 update.
Microsoft stated that the issue was limited to physical commercial devices and did not impact home users or virtual machines. The company had previously investigated the matter and linked it to update installation failures rather than hardware defects or malware activity.
In January 2026, Microsoft released an optional non-security preview update, KB5074105, which was designed to prevent additional devices from entering an improper state. That update helped reduce further impact but did not fully remediate systems that had already become unbootable.
February Patch Tuesday Delivers Full Resolution
The company has now confirmed that the issue is fully resolved in the Windows 11 KB5077181 update released on February 10, 2026. This update was part of the regular Patch Tuesday release cycle and includes fixes to address the boot failure condition.
Devices that install KB5077181 or later updates should no longer encounter the startup issue related to the earlier failed installations. Microsoft indicated that the resolution applies to affected versions of Windows 11 and prevents systems from becoming unbootable due to the prior update sequence.
However, systems that became unbootable before the February update may still require additional remediation steps. Microsoft has advised enterprise customers with impacted devices to contact Microsoft Support for Business for assistance in restoring system stability.
From a cybersecurity and operations perspective, the incident highlights the importance of update validation and monitoring within enterprise environments. Failed update rollbacks can leave systems in inconsistent states, increasing the risk of service disruption during subsequent patch cycles.
Organizations managing Windows 11 deployments are encouraged to review update histories, ensure that the Windows 11 KB5077181 update is applied, and verify that affected endpoints are operating normally. Maintaining consistent patch management processes and monitoring for abnormal restart behavior can help reduce operational risk tied to update-related issues.
With the February update now available, Microsoft has marked the boot failure issue as resolved for supported Windows 11 versions.
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