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TI-2026-17160 Aliases CVE-2026-21251GHSA-6q2h-rrfg-fm75

Cluster Client Failover (CCF) Elevation of Privilege Vulnerability

Priority LOW 36CWE-416Published · Updated

Key facts

Attack vector
Local
Privileges required
Low
User interaction
None
Attack complexity
Low
Impact type
Privilege escalation
Confidentiality · integrity · availability
High · High · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Microsoft. Impact type from Microsoft.

Summary

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

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00439 38th percentileScored 2026-11-07
Fix Fixed Microsoft: 7 updates

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
MicrosoftWindows Server 201610.0.14393.0 to before 10.0.14393.886810.0.14393.8868Patch availableCNA
MicrosoftWindows Server 2016 (Server Core installation)10.0.14393.0 to before 10.0.14393.886810.0.14393.8868Patch availableCNA
MicrosoftWindows Server 201910.0.17763.0 to before 10.0.17763.838910.0.17763.8389Patch availableCNA
MicrosoftWindows Server 2019 (Server Core installation)10.0.17763.0 to before 10.0.17763.838910.0.17763.8389Patch availableCNA
MicrosoftWindows Server 202210.0.20348.0 to before 10.0.20348.477310.0.20348.4773Patch availableCNA
MicrosoftWindows Server 2022, 23H2 Edition (Server Core installation)10.0.25398.0 to before 10.0.25398.214910.0.25398.2149Patch availableCNA
MicrosoftWindows Server 202510.0.26100.0 to before 10.0.26100.3237010.0.26100.32370Patch availableCNA
MicrosoftWindows Server 2025 (Server Core installation)10.0.26100.0 to before 10.0.26100.3237010.0.26100.32370Patch availableCNA
  • Windows Server 2016 VendorMicrosoft Affected 10.0.14393.0 to before 10.0.14393.8868 Fixed in 10.0.14393.8868 Patch available CNA
  • Windows Server 2016 (Server Core installation) VendorMicrosoft Affected 10.0.14393.0 to before 10.0.14393.8868 Fixed in 10.0.14393.8868 Patch available CNA
  • Windows Server 2019 VendorMicrosoft Affected 10.0.17763.0 to before 10.0.17763.8389 Fixed in 10.0.17763.8389 Patch available CNA
  • Windows Server 2019 (Server Core installation) VendorMicrosoft Affected 10.0.17763.0 to before 10.0.17763.8389 Fixed in 10.0.17763.8389 Patch available CNA
  • Windows Server 2022 VendorMicrosoft Affected 10.0.20348.0 to before 10.0.20348.4773 Fixed in 10.0.20348.4773 Patch available CNA
  • Windows Server 2022, 23H2 Edition (Server Core installation) VendorMicrosoft Affected 10.0.25398.0 to before 10.0.25398.2149 Fixed in 10.0.25398.2149 Patch available CNA
  • Windows Server 2025 VendorMicrosoft Affected 10.0.26100.0 to before 10.0.26100.32370 Fixed in 10.0.26100.32370 Patch available CNA
  • Windows Server 2025 (Server Core installation) VendorMicrosoft Affected 10.0.26100.0 to before 10.0.26100.32370 Fixed in 10.0.26100.32370 Patch available CNA

CPE configurations NVD · 5

CPEVersionsRoleVendor
cpe:2.3:o:microsoft:windows_server_2016:*:*:*:*:*:*:*:*before 10.0.14393.8868VulnerableMicrosoft
cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:*before 10.0.17763.8389VulnerableMicrosoft
cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:*before 10.0.20348.4711VulnerableMicrosoft
cpe:2.3:o:microsoft:windows_server_2022_23h2:*:*:*:*:*:*:*:*before 10.0.25398.2149VulnerableMicrosoft
cpe:2.3:o:microsoft:windows_server_2025:*:*:*:*:*:*:*:*before 10.0.26100.32313VulnerableMicrosoft
  • cpe:2.3:o:microsoft:windows_server_2016:*:*:*:*:*:*:*:* Versions before 10.0.14393.8868 Vulnerable ·Microsoft
  • cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:* Versions before 10.0.17763.8389 Vulnerable ·Microsoft
  • cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:* Versions before 10.0.20348.4711 Vulnerable ·Microsoft
  • cpe:2.3:o:microsoft:windows_server_2022_23h2:*:*:*:*:*:*:*:* Versions before 10.0.25398.2149 Vulnerable ·Microsoft
  • cpe:2.3:o:microsoft:windows_server_2025:*:*:*:*:*:*:*:* Versions before 10.0.26100.32313 Vulnerable ·Microsoft

Remediation

Microsoft 7 updates

  • KB5075999
    Security Update
    • Windows 10 Version 1607 for 32-bit Systems 10.0.14393.8868
    • Windows 10 Version 1607 for x64-based Systems 10.0.14393.8868
    • Windows Server 2016 10.0.14393.8868
    • Windows Server 2016 (Server Core installation) 10.0.14393.8868
  • KB5075943
    Security Hotpatch Update
    • Windows Server 2022 10.0.20348.4711
    • Windows Server 2022 (Server Core installation) 10.0.20348.4711
  • KB5075942
    Security Hotpatch Update
    • Windows Server 2025 10.0.26100.32313
    • Windows Server 2025 (Server Core installation) 10.0.26100.32313
Show 4 more Microsoft updates
  • KB5075906
    Security Update
    • Windows Server 2022 10.0.20348.4773
    • Windows Server 2022 (Server Core installation) 10.0.20348.4773
  • KB5075904
    Security Update
    • Windows 10 Version 1809 for 32-bit Systems 10.0.17763.8389
    • Windows 10 Version 1809 for x64-based Systems 10.0.17763.8389
    • Windows Server 2019 10.0.17763.8389
    • Windows Server 2019 (Server Core installation) 10.0.17763.8389
  • KB5075899
    Security Update
    • Windows Server 2025 10.0.26100.32370
    • Windows Server 2025 (Server Core installation) 10.0.26100.32370
  • KB5075897
    Security Update
    • Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.2149

Vendor assessments

Microsoft

Microsoft's page for this CVE →

Impact
Elevation of Privilege
Exploited
No
Publicly disclosed
No
Exploitability
Exploitation Unlikely

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-21251
  2. 2026-10-03 Alias added: GHSA-6q2h-rrfg-fm75

References

Patch 1

  • TI-2026-26194 Windows Internet Key Exchange (IKE) Service Extensions Remote Code Execution Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2025-36863 Windows Server Update Service (WSUS) Remote Code Execution Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2020-01431 Netlogon Elevation of Privilege Vulnerability KEVCVSS 3.1CRITICAL 10.0
  • TI-2020-01310 Improper input validation in Microsoft Windows Server KEVCVSS 3.1CRITICAL 10.0
  • TI-2017-06077 Microsoft Windows XP SP3, Windows XP x64 XP2, Windows Server 2003 SP2, Windows Vista… KEVCVSS 3.1CRITICAL 9.8
  • TI-2020-01009 Improper input validation in Microsoft Windows Server KEVCVSS 3.1CRITICAL 9.0
See all 6400 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences