CVE-2026-40402
Critical CVSS 9.3Published 2026-05-12 ยท last changed 2026-06-17
The fix
Microsoft fixes this in updatesKB5087420, KB5093998, KB5087545, KB5087424. The fixed build differs per Windows version, so the row that matters is the one matching the machine you are looking at.
| Windows version | Fixed in build | Update | Released |
|---|---|---|---|
| Windows 11 Version 23H2 for ARM64-based Systems | 10.0.22631.7079 | KB5087420 | 2026-09-18 |
| Windows 11 Version 23H2 for x64-based Systems | 10.0.22631.7219 | KB5093998 | 2026-09-18 |
| Windows Server 2022 | 10.0.20348.5139 | KB5087545, KB5087424 | 2026-09-18 |
| Windows Server 2022 (Server Core installation) | 10.0.20348.5139 | KB5087545, KB5087424 | 2026-09-18 |
Having the KB is not the same as knowing whether a machine has it. Windows updates supersede each other, so the update you installed often covers a fix that shipped in an earlier one. Paste your build into the patch checker and it walks that chain for you.
What it is
Use after free in Windows Hyper-V allows an unauthorized attacker to elevate privileges locally.
Sources
CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H