CVE-2026-40402

Windows Hyper-V Elevation of Privilege Vulnerability

CVE-2026-40402 is fixed in 4 products on 1 platform, first by KB5087420, released May 12, 2026. It is not reported as exploited. Patch Radar priority: Urgent.

Urgent

CVSS

9.3

Critical

Exploitation

None reported

Exploitation Less Likely

CISA KEV

Not listed

Not in the Known Exploited Vulnerabilities catalog

EPSS

0.0033

26th percentile

<p>Use after free in Windows Hyper-V allows an unauthorized attacker to elevate privileges locally.</p>

Where it's fixed

Product	Fixed in	Fix	Released
Microsoft
Windows 11 Version 23H2 for ARM64-based Systems	22631.7079	KB5087420	May 12, 2026
Windows 11 Version 23H2 for x64-based Systems	22631.7219	KB5093998	Jun 9, 2026
Windows Server 2022	20348.5074	KB5087424	May 12, 2026
Windows Server 2022	20348.5139	KB5087545	May 12, 2026
Windows Server 2022 (Server Core installation)	20348.5074	KB5087424	May 12, 2026
Windows Server 2022 (Server Core installation)	20348.5139	KB5087545	May 12, 2026

Details

Published
May 12, 2026
Weakness
Use After Free
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40402

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