Microsoft confirms Windows 11 bug can block access to the C: drive on some Samsung PCs

Microsoft has confirmed a Windows 11 issue that can make the system drive, usually C:, inaccessible on some Samsung devices after the February 2026 security update. The company says affected users may see the error “C:\ is not accessible – Access denied,” which can stop apps from launching and block access to files.

The issue affects Windows 11 version 24H2 and 25H2 on some Samsung consumer devices, with Microsoft saying it has been seen mainly on Samsung Galaxy Book 4 models and other Samsung consumer PCs. The company also says the problem has been reported in Brazil, Portugal, South Korea, and India.

This is more than a minor app bug. Microsoft says routine actions such as opening files, launching apps, or performing administrative tasks can trigger the problem. In some cases, users also cannot elevate privileges, uninstall updates, or collect logs because permission failures spread across the system.

What Microsoft says is happening

Microsoft added the issue to the official Windows release health page for Windows 11 24H2 on March 13, 2026. The company says it received reports that some Samsung device models lose access to the C: drive after installing the February 2026 security update KB5077181 and later updates. The affected build listed by Microsoft is OS Build 26100.7840.

According to Microsoft, affected users may be unable to start apps including Outlook, Office apps, web browsers, system utilities, and Quick Assist. That makes the issue especially serious because it can disrupt both personal use and work tasks with no special trigger beyond normal use.

Microsoft’s latest investigation suggests the issue may relate to the Samsung Share app, though the company says the root cause has not yet been fully validated. Microsoft is investigating the reports together with Samsung.

Affected systems at a glance

Source: Microsoft Windows release health.

What users are seeing

• “C:\ is not accessible – Access denied”
• Apps fail to open
• File access breaks
• Admin actions may fail
• In some cases, users cannot uninstall updates or gather logs

These symptoms come directly from Microsoft’s known issue entry.

Why this bug matters

When the root of the system drive becomes inaccessible, Windows can start to fail in several places at once. Apps stored on C: may not launch, admin tools may stop working, and troubleshooting becomes much harder because the same permissions issue can block the tools needed to fix the system. This explanation is an inference based on the symptoms Microsoft listed.

The fact that Microsoft linked the issue to Samsung consumer devices rather than all Windows 11 PCs suggests this may involve an interaction between the Windows update and Samsung software, not a general Windows storage failure. Microsoft has not yet confirmed that conclusion, but its reference to Samsung Share points in that direction.

Is there a fix yet?

Not yet. Microsoft currently lists the issue as “Investigating” and says it is reviewing reports with Samsung to determine whether the problem is caused by Windows updates. The company has not published an official workaround in the release health entry.

That means users should be careful with unofficial fixes posted on forums or social platforms, especially any workaround that changes core permissions on the root of the system drive. Microsoft’s official page does not recommend such a step.

What affected users should do now

• Check whether your PC is a Samsung Galaxy Book 4 or another Samsung consumer device
• Confirm whether KB5077181 or a later update installed before the problem started
• Avoid changing root drive permissions based on unverified forum posts
• Use official Microsoft support channels if the PC becomes unusable
• Watch the Windows release health page for Microsoft’s fix or workaround

The last two steps are practical guidance based on Microsoft’s current “Investigating” status and support references on the release health page.

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