Windows 11 Boot Issue Resolved with February 2026 Update
Microsoft has announced a resolution to a critical bug impacting certain Windows 11 systems. The issue caused a failure to boot, presenting users with an “UNMOUNTABLE_BOOT_VOLUME” error following the installation of recent security updates. The fix was delivered via the February 2026 Patch Tuesday release, specifically within the KB5077181 security update, issued on February 10, 2026.
The problem stemmed from complications arising from failed updates released in December 2025. Affected devices, running either the 25H2 or 24H2 versions of Windows 11, experienced boot failures after applying the January 13, 2026, security update KB5074109, or subsequent releases. Users encountered a black screen accompanied by a system message indicating a need to restart.
Impact on Commercial Systems
This boot problem was isolated to a limited number of commercial Windows 11 devices, specifically physical machines. Microsoft confirmed they did not receive reports of the issue affecting home users or those utilizing virtual machines. The root cause was traced back to the December 2025 update, which left systems in an unstable condition when the installation process was rolled back.
Attempting to install further Windows updates on devices left in this “improper state” could then render the system completely unbootable. This created a cascading effect, potentially disrupting business operations reliant on these affected machines. The company acknowledged the severity of the issue and prioritized a solution for enterprise environments.
Initial Mitigation and Full Resolution
Prior to the February 2026 Patch Tuesday update, Microsoft released an initial mitigation in the form of the optional, non-security preview update KB5074105 on January 29, 2026. This preliminary fix aimed to prevent additional systems from becoming vulnerable to the boot failure.
According to a private advisory shared with Susan Bradley of Ask Woody, the issue is now considered fully resolved with the release of KB5077181 and subsequent updates. “This issue is fully resolved in the Windows security update released on February 10, 2026 (the Resolved KBs listed above), and later updates,” stated Microsoft’s official communication. However, systems already experiencing unbootable states may still require intervention.
Support for Affected Enterprises
Microsoft is advising enterprise customers who continue to experience boot failures to reach out to Microsoft Support for Business for assistance. The support team can provide guidance and tools to restore system stability and functionality. It remains unclear why the company did not publicly disseminate this advisory, a practice typically followed for other known Windows issues.
