CVE-2026-21251

Cluster Client Failover (CCF) Elevation of Privilege Vulnerability

CVE-2026-21251 is fixed in 9 products on 1 platform, first by KB5075999, released February 10, 2026. It is not reported as exploited. Patch Radar priority: High.

High

CVSS

7.8

Important

Exploitation

None reported

Exploitation Unlikely

CISA KEV

Not listed

Not in the Known Exploited Vulnerabilities catalog

EPSS

0.0044

38th percentile

<p>Use after free in Windows Cluster Client Failover allows an authorized attacker to elevate privileges locally.</p>

Where it's fixed

Product	Fixed in	Fix	Released
Microsoft
Windows Server 2016	14393.8868	KB5075999	Feb 10, 2026
Windows Server 2016 (Server Core installation)	14393.8868	KB5075999	Feb 10, 2026
Windows Server 2019	17763.8389	KB5075904	Feb 10, 2026
Windows Server 2019 (Server Core installation)	17763.8389	KB5075904	Feb 10, 2026
Windows Server 2022	20348.4773	KB5075906	Feb 10, 2026
Windows Server 2022	20348.4711	KB5075943	Feb 10, 2026
Windows Server 2022 (Server Core installation)	20348.4773	KB5075906	Feb 10, 2026
Windows Server 2022 (Server Core installation)	20348.4711	KB5075943	Feb 10, 2026
Windows Server 2022, 23H2 Edition (Server Core installation)	25398.2149	KB5075897	Feb 10, 2026
Windows Server 2025	26100.32313	KB5075942	Feb 10, 2026
Windows Server 2025	26100.32370	KB5075899	Feb 10, 2026
Windows Server 2025 (Server Core installation)	26100.32313	KB5075942	Feb 10, 2026
Windows Server 2025 (Server Core installation)	26100.32370	KB5075899	Feb 10, 2026

Details

Published
February 10, 2026
Weakness
Use After Free
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21251

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