Windows 11 Bug Locks Users Out of System Drive C

What Happened

Microsoft has confirmed a critical bug affecting Windows 11 users, particularly those with certain Samsung devices. After installing the February 2026 security update (KB5077181), users found that their system drive^? (C:) became completely inaccessible. This issue prevents users from launching applications or performing routine tasks, leading to significant disruption. The error message displayed is "C:\ is not accessible – Access denied," which effectively locks users out of their own system drive^?.

The problem is not limited to specialized operations. Even basic actions like opening files or launching applications trigger the error. In severe cases, users cannot elevate privileges or uninstall updates, making it nearly impossible to fix the issue without external help. Microsoft is currently investigating the problem in collaboration with Samsung, as it primarily affects devices like the Samsung Galaxy Book 4.

Who's Affected

Reports of this bug have emerged from several regions, including Brazil, Portugal, South Korea, and India. Affected users primarily run Windows 11 versions 24H2 and 25H2. Notably, enterprise administrators have flagged the issue on platforms like Reddit, indicating that Galaxy Book laptops within Active Directory domains cannot modify NTFS permissions^?, even with administrator rights. This widespread impact highlights the urgency of the situation for both individual users and businesses relying on these devices.

What Data Was Exposed

While the bug does not directly expose personal data, it severely limits access to the system drive^?, which contains critical applications and files. Users are unable to access essential tools like Microsoft Outlook and other Office applications, as well as system utilities. Secondary issues have also been reported, such as trackpad driver failures and the inability to open PowerShell, which resides on the inaccessible C: drive. The root cause is believed to involve corrupted or incorrectly applied Access Control Lists (ACLs) on the system drive^?, potentially linked to the Samsung Share application.

What You Should Do

As of now, Microsoft has classified the issue as "Investigating" and has not released an official fix. Users are strongly advised against attempting unofficial workarounds, such as reassigning C: drive ownership to the "Everyone" group, as this can compromise system security. Instead, affected users should wait for an official patch from Microsoft. The company has committed to providing updates as the investigation progresses, emphasizing the importance of maintaining security while resolving this critical issue.