Microsoft has issued a warning about the recently released KB5077181 update advising that the cumulative update can cause the C: drive of some devices to become inaccessible.
The impact of the issue is limited by the fact that the problem seems to stem from the interplay between the KB5077181 update and an app that is installed on some Samsung devices. But while the number of affected users may be limited by this fact, the impact on those who are affected remains large.
In a message posted to the Windows release health page, Microsoft explains that it “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”.
It goes on to explain:
Microsoft and Samsung investigated these reports and concluded that the symptoms were caused by an issue in the Samsung Galaxy Connect app. While the reports coincided with recent March Patch Tuesday timing, investigation confirmed the issue is not caused by current or previous Windows monthly updates. The issue has been observed on Samsung Galaxy Book 4 and Samsung Desktop models running Windows 11, versions 24H2 and 25H2, including NP750XGJ, NP750XGL, NP754XGJ, NP754XFG, NP754XGK, DM500SGA, DM500TDA, DM500TGA, and DM501SGA.
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.
Although there is not a proper fix or workaround available yet, Microsoft says: “The affected Samsung Galaxy Connect application was temporarily removed from the Microsoft Store to prevent further installations. Samsung has republished a stable previous version of the application to stop recurrence on additional devices. Recovery options for devices already impacted remain limited, and Samsung continues to evaluate remediation approaches with Microsoft’s support”.
As for what happens next, Microsoft and Samsung are working together to try to come up with a fix:
Next steps: Microsoft is collaborating with Samsung’s efforts to develop and validate solutions for devices that have already been affected. We will update this documentation as more information becomes available and Samsung releases further public guidance. For device specific assistance, please contact Samsung’s support channels.
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