MSRC-CVE-2026-83991 — Windows Cloud Files Mini Filter Driver Tampering Vulnerability

Summary

Impact: Tampering. Microsoft rating: Important. Not known to be exploited — Exploitation Less Likely. Customer action: Required.

Details

What could an attacker achieve by exploiting this vulnerability?
An attacker could exploit this vulnerability to make unauthorized modifications to protected system data. This could allow the attacker to alter system state or configuration beyond their normal privileges.

Security updates
10.0.17763.9245 — https://support.microsoft.com/help/5122876
10.0.20348.5622 — https://support.microsoft.com/help/5122882
10.0.19044.7725 — https://support.microsoft.com/help/5122878
10.0.26100.33438 — https://support.microsoft.com/help/5122871
10.0.26200.9445 — https://support.microsoft.com/help/5124008
10.0.22631.7582 — https://support.microsoft.com/help/5122880
10.0.28000.2954 — https://support.microsoft.com/help/5124012

Vulnerabilities 1

Medium 5.5

CVE-2026-83991 Public exploit

Windows Cloud Files Mini Filter Driver Tampering Vulnerability

Missing authentication for critical function in Windows Cloud Files Mini Filter Driver allows an authorized attacker to perform tampering locally.

Microsoft Windows Server 2019 Windows Server 2019 (Server Core installation) Windows 10 Version 1809 Windows

Sep 8, 2026

Revision history

2026-09-08 #1
Information published.

References

CVE-2026-83991 Windows Cloud Files Mini Filter Driver Tampering Vulnerability - HTML
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-83991
Microsoft Exploitability Index
https://www.microsoft.com/en-us/msrc/exploitability-index?rtc=1
Microsoft Support Lifecycle
https://support.microsoft.com/lifecycle
Common Vulnerability Scoring System
https://www.first.org/cvss