Windows Fast FAT File System Driver Information Disclosure Vulnerability
CVE-2026-70277
Summary
Incorrect authorization in Windows Container Isolation FS Filter Driver (unionfs.sys) allows an authorized attacker to disclose information locally.
Products covered
Windows 11 version 26H1 for x64-based Systems
Windows 11 Version 26H1 for ARM64-based Systems
Remediation
Install KB5121000.
Vendor-listed fixes
10.0.28000.2704
CVEs in this advisory 1
Update history
What changed in later vendor updates
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- The vendor changed its remediation guidance.
Updates
- Published by Microsoft Security Response Center
The publication date reported by the vendor.
- Added to SecurityAlert
We collected the advisory from the official source.
- Confirmed at the source
Our collector saw this advisory during a later source check.