Microsoft has updated the official Windows 11 documentation with details about a newly discovered bug that may ruin your day if you have a certain PC and try to access the system drive C. According to Microsoft, installing the February 2026 Patch Tuesday update (KB5077181) could lead to the error "C:\is not accessible - Access denied."
While drive C is not something you want to open every day, the problem goes a bit deeper than just opening File Explorer. Microsoft says that because of the bug, some apps cannot start, and those include popular stuff like Outlook, browsers, system utilities, and more. The issue effectively cripples your computer, as common actions like accessing files, executing common tasks, elevating privileges and doing other daily things.
Although the bug sounds absolutely terrifying, the good news is that not every Windows 11 system is affected. Microsoft says that the bug is "predominantly observed" on Samsung laptops, particularly on the Samsung Galaxy Book4 and other models in countries like Brazil, Portugal, Korea, and India. It is possible that the Samsung Share application could be the reason, but Microsoft is not ready to share exact details. Microsoft is investigating the problem, so expect to hear from them soon.
Here is what Microsoft says in the official documentation:
Microsoft has received reports of an issue in which some Samsung device models lose access to the C: drive after installing the February 2026 security update (KB5077181) and subsequent updates. Users might encounter the error, “C:\ is not accessible – Access denied”, which prevents access to files and blocks the launch of some applications including Outlook, Office apps, web browsers, system utilities and Quick Assist.
Affected devices encounter the issue when users execute common actions, such as accessing files, launching applications, or performing administrative tasks, and do not require any specific user action beyond routine operations. In some cases, users are also unable to elevate privileges, uninstall updates, or collect logs due to permission failures.
This issue has been reported across multiple regions, including Brazil, Portugal, Korea, and India, and is predominantly observed on Samsung Galaxy Book 4 and other Samsung consumer devices. Latest investigations indicate that the issue may be related to the Samsung Share application, though the root cause has not yet been fully validated.
As for the affected systems, only Windows 11 versions 24H2 and 25H2 were hit. If you are on Windows 10 or Windows 11 23H2 and older, the problem should not affect your Samsung device. Frustrated users on Reddit claim that changing ownership of the Drive C and its folders/files fixes the problem, but it is a risky thing that should be done only in emergencies. For most users, if rolling back the update did not yield any results, the best course of action is to wait for Microsoft to fix the issue.
Update March 16, 2026: Microsoft published its official workaround for the affected systems.