Microsoft has identified a significant problem impacting Windows 11 users, particularly those utilizing specific Samsung devices. This issue, arising after the February 2026 security update, renders the system drive (C:) completely inaccessible. Currently, Microsoft is collaborating with Samsung to resolve this.
Details of the Bug and Affected Devices
The problem stems from the February 2026 Patch Tuesday update, known as KB5077181, which upgrades the OS to Build 26100.7840. Upon installation, Samsung devices display an error message stating: “C: is not accessible – Access denied.” This error prevents users from accessing their system drive, thereby blocking the use of applications like Microsoft Outlook, Office apps, and web browsers.
Routine operations such as opening files or launching applications trigger this issue, and severe cases prevent users from escalating privileges or uninstalling updates. This complicates self-remediation efforts without external assistance.
Geographical Impact and Community Response
The bug is predominantly reported on Samsung Galaxy Book 4 and other Samsung consumer devices, with incidents surfacing in countries such as Brazil, Portugal, South Korea, and India. Affected Windows versions include Windows 11 versions 24H2 and 25H2, while server platforms remain unaffected.
Enterprise administrators have voiced concerns on platforms like Reddit’s r/sysadmin, noting that Galaxy Book laptops within Active Directory domains cannot modify NTFS permissions, even with administrator rights.
Potential Causes and Official Guidance
Microsoft’s investigation suggests that the Samsung Share application may contribute to the issue, although this has yet to be confirmed. The root cause is suspected to involve corrupted or incorrectly applied Access Control Lists (ACLs) on the system drive.
As of March 13, 2026, Microsoft continues to investigate, with no official fix or workaround released. A workaround from a Reddit user, purportedly a Samsung technician in Brazil, recommends reassigning C: drive ownership to the “Everyone” group. However, Microsoft advises against this due to potential security risks.
Microsoft recommends waiting for an official patch and has promised to provide further updates as investigations continue. Follow us on Google News, LinkedIn, and X for the latest cybersecurity updates, or contact us to share your stories.
