Vulnerability · Published Feb 10, 2026 · Assigned by microsoft
CVE-2026-21251Cluster Client Failover (CCF) Elevation of Privilege Vulnerability
High 7.8
In plain English
A high-severity use-after-free in Windows Server 2016 from Microsoft. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 38% of all known vulnerabilities).
Severity (CVSS 3.1)7.8High
Exploit odds (30 days)0.4%top 61.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
Use after free in Windows Cluster Client Failover allows an authorized attacker to elevate privileges locally.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Microsoft | Windows Server 2016 | 10.0.14393.0 – before 10.0.14393.8868 |
| Microsoft | Windows Server 2016 (Server Core installation) | 10.0.14393.0 – before 10.0.14393.8868 |
| Microsoft | Windows Server 2019 | 10.0.17763.0 – before 10.0.17763.8389 |
| Microsoft | Windows Server 2019 (Server Core installation) | 10.0.17763.0 – before 10.0.17763.8389 |
| Microsoft | Windows Server 2022 | 10.0.20348.0 – before 10.0.20348.4773 |
| Microsoft | Windows Server 2022, 23H2 Edition (Server Core installation) | 10.0.25398.0 – before 10.0.25398.2149 |
| Microsoft | Windows Server 2025 | 10.0.26100.0 – before 10.0.26100.32370 |
| Microsoft | Windows Server 2025 (Server Core installation) | 10.0.26100.0 – before 10.0.26100.32370 |
Weakness: CWE-416 · Vector: 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
References
- Cluster Client Failover (CCF) Elevation of Privilege Vulnerability vendor-advisory, patch