CVE-2026-21255 — Windows Hyper-V Security Feature Bypass Vulnerability

Executive Summary

Improper access control in Windows Hyper-V allows an authorized attacker to bypass a security feature locally.

Overview

8.8

CVSS HIGH

Important

MS Severity

Not Exploited

MS Exploit Status

Less Likely

MS Exploit Likelihood

Category Security Feature Bypass

Released Feb 10 2026

Last Updated Feb 10 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00356 — 0.27324 percentile

CVSS Vector

ATTACK VECTOR

Local

ATTACK COMPLEXITY

Low

PRIVILEGES REQUIRED

Low

USER INTERACTION

None

SCOPE

Changed

Temporal Score: 7.7

EPSS Score

0.00356

probability of exploitation in the next 30 days

0.27324 percentile - updated 2026-06-20

View on FIRST.org

Affected Products

21 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 10 Version 1607 for x64-based Systems	`5075999 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 10 Version 1809 for x64-based Systems	`5075904 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 10 Version 21H2 for x64-based Systems	`5075912 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 10 Version 22H2 for x64-based Systems	`5075912 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 23H2 for ARM64-based Systems	`5075941 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 23H2 for x64-based Systems	`5075941 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 24H2 for ARM64-based Systems	`5077181 (Security Update) 5077212 (Security Hotpatch Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 24H2 for x64-based Systems	`5077212 (Security Hotpatch Update) 5077181 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 25H2 for ARM64-based Systems	`5077181 (Security Update) 5077212 (Security Hotpatch Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 25H2 for x64-based Systems	`5077181 (Security Update) 5077212 (Security Hotpatch Update)`	Important	Security Feature Bypass	Yes
Windows 11 Version 26H1 for ARM64-based Systems	`5077179 (Security Update)`	Important	Security Feature Bypass	Yes
Windows 11 version 26H1 for x64-based Systems	`5077179 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2016	`5075999 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2016 (Server Core installation)	`5075999 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2019	`5075904 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2019 (Server Core installation)	`5075904 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2022	`5075906 (Security Update) 5075943 (Security Hotpatch Update)`	Important	Security Feature Bypass	Yes
Windows Server 2022 (Server Core installation)	`5075906 (Security Update) 5075943 (Security Hotpatch Update)`	Important	Security Feature Bypass	Yes
Windows Server 2022, 23H2 Edition (Server Core installation)	`5075897 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2025	`5075899 (Security Update) 5075942 (Security Hotpatch Update)`	Important	Security Feature Bypass	Yes
Windows Server 2025 (Server Core installation)	`5075899 (Security Update) 5075942 (Security Hotpatch Update)`	Important	Security Feature Bypass	Yes

Patches

10 patches

Article	Type	Restart
`5075999`	Security Update	Yes
`5075904`	Security Update	Yes
`5075912`	Security Update	Yes
`5075941`	Security Update	Yes
`5077181 (Security Update) 5077212`	Security Update	Yes
`5077212 (Security Hotpatch Update) 5077181`	Security Hotpatch Update	Yes
`5077179`	Security Update	Yes
`5075906 (Security Update) 5075943`	Security Update	Yes
`5075897`	Security Update	Yes
`5075899 (Security Update) 5075942`	Security Update	Yes

Known Exploits

No known exploits have been linked for this CVE yet. When available, exploit references will be sourced from public repositories and may be unverified, incomplete, or non-functional. Always review code carefully before use in any environment.

Acknowledgments

Sai Ganesh Ramachandran with Microsoft

References

MSRC Advisory MITRE NVD