High 7.8Published Feb 10, 2026

CVE-2026-21251Cluster Client Failover (CCF) Elevation of Privilege Vulnerability

Updated under an hour ago (Oct 28, 2026, 5:25 PM ET)

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It affects Microsoft Windows Server 2016 and 4 other products. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for Microsoft Windows Server 2016

Exploited in the last 30 days

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

CVSS: 7.8 HIGH (v3.1, CNA)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
Weakness (CWE): CWE-416
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: microsoft
NVD analysis: Analyzed
Record last updated: Aug 19, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Microsoft Windows Server 2016 microsoft:windows_server_2016 (from the name)	from 10.0.14393.0 before 10.0.14393.8868	CNA record
Microsoft Windows Server 2019 microsoft:windows_server_2019 (from the name)	from 10.0.17763.0 before 10.0.17763.8389	CNA record
Microsoft Windows Server 2022 microsoft:windows_server_2022 (from the name)	from 10.0.20348.0 before 10.0.20348.4773	CNA record
Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) microsoft:windows_server_2022_23h2	from 10.0.25398.0 before 10.0.25398.2149	CNA record
Microsoft Windows Server 2025 microsoft:windows_server_2025 (from the name)	from 10.0.26100.0 before 10.0.26100.32370	CNA record
microsoft windows_server_2016 microsoft:windows_server_2016	before 10.0.14393.8868	NVD
microsoft windows_server_2019 microsoft:windows_server_2019	before 10.0.17763.8389	NVD
microsoft windows_server_2022 microsoft:windows_server_2022	before 10.0.20348.4711	NVD
microsoft windows_server_2022_23h2 microsoft:windows_server_2022_23h2	before 10.0.25398.2149	NVD
microsoft windows_server_2025 microsoft:windows_server_2025	before 10.0.26100.32313	NVD

References

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21251	vendor-advisory, patch

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.