CVE-2026-21251: Microsoft Windows Server 2016

High severity, CVSS 7.8. EPSS: 0.4% chance of exploitation in the next 30 days.

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

Affected products

• Microsoft Windows Server 2016: before 10.0.14393.8868 (fixed in 10.0.14393.8868)
• Microsoft Windows Server 2019: before 10.0.17763.8389 (fixed in 10.0.17763.8389)
• Microsoft Windows Server 2022: before 10.0.20348.4711 (fixed in 10.0.20348.4711)
• Microsoft Windows Server 2022 23h2: before 10.0.25398.2149 (fixed in 10.0.25398.2149)
• Microsoft Windows Server 2025: before 10.0.26100.32313 (fixed in 10.0.26100.32313)

Published 2026-02-10. Last modified 2026-06-17.