CVE-2026-21251

Cluster Client Failover (CCF) Elevation of Privilege Vulnerability

State: Published
Severity: 7.8 High
Published: Feb 10, 2026
Updated: Aug 19, 2026
Reserved: Dec 11, 2025

Description

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

Scores

CVSS	Score	Vector	Source
3.1	7.8 High	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C	microsoft

Weaknesses

CWE-416 Use After Free

Affected Products

Product	Versions
Windows Server 2016Microsoft	10.0.14393.0 to before 10.0.14393.8868Affected
Windows Server 2016 (Server Core installation)Microsoft	10.0.14393.0 to before 10.0.14393.8868Affected
Windows Server 2019Microsoft	10.0.17763.0 to before 10.0.17763.8389Affected
Windows Server 2019 (Server Core installation)Microsoft	10.0.17763.0 to before 10.0.17763.8389Affected
Windows Server 2022Microsoft	10.0.20348.0 to before 10.0.20348.4773Affected
Windows Server 2022, 23H2 Edition (Server Core installation)Microsoft	10.0.25398.0 to before 10.0.25398.2149Affected
Windows Server 2025Microsoft	10.0.26100.0 to before 10.0.26100.32370Affected
Windows Server 2025 (Server Core installation)Microsoft	10.0.26100.0 to before 10.0.26100.32370Affected

References

Cluster Client Failover (CCF) Elevation of Privilege Vulnerabilityvendor-advisorypatch

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