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

Weakness CWE-284: Improper Access Control

Released Feb 10 2026

Last Updated Feb 10 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00356 — 0.28231 percentile

NVD CVSS 8.8 HIGH — matches MSRC

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C

ATTACK VECTOR

Local

ATTACK COMPLEXITY

Low

PRIVILEGES REQUIRED

Low

USER INTERACTION

None

SCOPE

Changed

CONFIDENTIALITY

High

INTEGRITY

High

AVAILABILITY

High

EXPLOIT CODE MATURITY

Unproven

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 7.7

EPSS Score

0.00356

probability of exploitation in the next 30 days

0.28231 percentile - updated 2026-07-25

View on FIRST.org

Affected Products

13 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 5073379 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26100.7840 10.0.26100.7781 Yes None Windows 11 Version 24H2 for x64-based Systems 5077212 (Security Hotpatch Update) 5077181 (Security Update) Important Security Feature Bypass 5074109 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26100.7781 10.0.26100.7840 Yes None Windows 11 Version 25H2 for ARM64-based Systems 5077181 (Security Update) 5077212 (Security Hotpatch Update) Important Security Feature Bypass 5074109 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26200.7840 10.0.26200.7781 Yes None Windows 11 Version 25H2 for x64-based Systems 5077181 (Security Update) 5077212 (Security Hotpatch Update) Important Security Feature Bypass 5074109 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26200.7840 10.0.26200.7781 Yes None 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 5073457 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.20348.4773 10.0.20348.4711 Yes None Windows Server 2022 (Server Core installation) 5075906 (Security Update) 5075943 (Security Hotpatch Update) Important Security Feature Bypass 5073457 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.20348.4773 10.0.20348.4711 Yes None Windows Server 2022, 23H2 Edition (Server Core installation)	`5075897 (Security Update)`	Important	Security Feature Bypass	Yes

Patches

6 patches

Article	Type	Restart
`5075999`	Security Update	Yes
`5075904`	Security Update	Yes
`5075912`	Security Update	Yes
`5075941`	Security Update	Yes
`5077179`	Security Update	Yes
`5075897`	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