cve 2026 21251

CVE-2026-21251 is a Cluster Client Failover (CCF) elevation-of-privilege vulnerability affecting Windows Failover Clusters. Microsoft's Security Response Center has published an advisory with a high confidence rating, urging immediate attention from Windows administrators, security teams, and enterprise IT professionals who manage failover clusters in production environments. The vulnerability targets cluster membership components, potentially allowing an attacker to elevate privileges within the cluster. Hardening measures and patching are critical to mitigate risks. This tag covers discussions, advisories, and remediation steps related to CVE-2026-21251, focusing on Windows Server security and cluster resilience.