CVE tracker / CVE-2026-83991

CVE-2026-83991

CVE-2026-83991 is the Windows Cloud Files Mini Filter Driver Tampering Vulnerability. Microsoft rates it Important, CVSS 5.5. It is not in CISA's Known Exploited Vulnerabilities catalog. Published September 8, 2026.

Risk summary

MediumTampering

5.5

CVSS v3 base

0.3%

EPSS: chance of exploitation in 30 days

Medium

Severity

Important

Microsoft's rating

Less Likely

Microsoft: exploitation

In CISA KEV

Microsoft describes it: “Missing authentication for critical function in Windows Cloud Files Mini Filter Driver allows an authorized attacker to perform tampering locally.”

How to fix it

Microsoft lists 22 affected products and the update that fixes each:

KB5122871 · fixed build 10.0.26100.33438
Windows Server 2025, Windows Server 2025 (Server Core installation)
KB5122876 · fixed build 10.0.17763.9245
Windows Server 2019 (Server Core installation), Windows 10 Version 1809 for x64-based Systems, Windows Server 2019, Windows 10 Version 1809 for 32-bit Systems
KB5122878 · fixed build 10.0.19045.7725, 10.0.19044.7725
Windows 10 Version 22H2 for 32-bit Systems, Windows 10 Version 22H2 for x64-based Systems, Windows 10 Version 22H2 for ARM64-based Systems, Windows 10 Version 21H2 for x64-based Systems, Windows 10 Version 21H2 for ARM64-based Systems, and 1 more
KB5122880 · fixed build 10.0.22631.7582
Windows 11 Version 23H2 for x64-based Systems, Windows 11 Version 23H2 for ARM64-based Systems
KB5122882 · fixed build 10.0.20348.5622
Windows Server 2022 (Server Core installation), Windows Server 2022
KB5124008 · fixed build 10.0.26100.9445, 10.0.26200.9445
Windows 11 Version 24H2 for x64-based Systems, Windows 11 Version 24H2 for ARM64-based Systems, Windows 11 Version 25H2 for x64-based Systems, Windows 11 Version 25H2 for ARM64-based Systems
KB5124012 · fixed build 10.0.28000.2954
Windows 11 Version 26H1 for ARM64-based Systems, Windows 11 version 26H1 for x64-based Systems

What Microsoft changed

September 8, 2026: Information published.

Details

Weakness: CWE-306: Missing Authentication for Critical Function
Publicly disclosed (Microsoft): No
Exploited (Microsoft): No
Known exploited (CISA KEV): Not listed
Published: September 8, 2026
Last revised: September 8, 2026

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References

Microsoft Security Update Guide NVD CVE record CWE

From Microsoft, CISA, NVD and FIRST data; the Microsoft details were read when this page was opened. Check the references above before you act.