CVE tracker / CVE-2026-21251
CVE-2026-21251
CVE-2026-21251 is the Cluster Client Failover (CCF) Elevation of Privilege Vulnerability. Microsoft rates it Important, CVSS 7.8. It is not in CISA's Known Exploited Vulnerabilities catalog. Published February 10, 2026.
Risk summary
Microsoft describes it: “Use after free in Windows Cluster Client Failover allows an authorized attacker to elevate privileges locally.”
How to fix it
Microsoft lists 9 affected products and the update that fixes each:
- KB5075897 · fixed build 10.0.25398.2149
Windows Server 2022, 23H2 Edition (Server Core installation) - KB5075899 · fixed build 10.0.26100.32370
Windows Server 2025, Windows Server 2025 (Server Core installation) - KB5075904 · fixed build 10.0.17763.8389
Windows Server 2019 (Server Core installation), Windows Server 2019 - KB5075906 · fixed build 10.0.20348.4773
Windows Server 2022 (Server Core installation), Windows Server 2022 - KB5075999 · fixed build 10.0.14393.8868
Windows Server 2016 (Server Core installation), Windows Server 2016
What Microsoft changed
- February 10, 2026: Information published.
Details
- Weakness
- CWE-416: Use After Free
- Publicly disclosed (Microsoft)
- No
- Exploited (Microsoft)
- No
- Known exploited (CISA KEV)
- Not listed
- Published
- February 10, 2026
- Last revised
- February 10, 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.