CVE tracker / CVE-2026-83999
CVE-2026-83999
CVE-2026-83999 is the Windows Resilient File System (ReFS) Deduplication Service Elevation of Privilege Vulnerab. Microsoft rates it Important, CVSS 7.0. It is not in CISA's Known Exploited Vulnerabilities catalog. Published September 8, 2026.
Risk summary
Microsoft describes it: “Improper link resolution before file access ('link following') in Windows Resilient File System (ReFS) Deduplication Service allows an authorized attacker to elevate privileges locally.”
How to fix it
Microsoft lists 8 affected products and the update that fixes each:
- KB5122871 · fixed build 10.0.26100.33438
Windows Server 2025, Windows Server 2025 (Server Core installation) - KB5124008 · fixed build 10.0.26100.9445, 10.0.26200.9445
Windows 11 Version 24H2 for x64-based Systems, Windows 11 Version 25H2 for x64-based Systems, Windows 11 Version 24H2 for ARM64-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-59: Improper Link Resolution Before File Access ('Link Following')
- Publicly disclosed (Microsoft)
- No
- Exploited (Microsoft)
- No
- Known exploited (CISA KEV)
- Not listed
- Published
- September 8, 2026
- Last revised
- September 8, 2026
Get told when this changes
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References
From Microsoft, CISA, NVD and FIRST data; the Microsoft details were read when this page was opened. Check the references above before you act.