What is the CVSS score of CVE-2026-21255?

CVE-2026-21255 has a CVSS 3.1 base score of 8.8 (High). CVSS vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H. EPSS exploitation probability: 0.0%.

Which versions of Windows are affected by CVE-2026-21255?

A high-severity vulnerability in Windows Hyper-V (CVE-2026-21255) allows authenticated attackers to bypass critical security controls on virtualized infrastructure.. A patch is available.

How to fix or mitigate CVE-2026-21255?

Within 24 hours: Inventory all Windows Hyper-V deployments and identify systems with direct user access; restrict administrative privileges to essential personnel only. Within 7 days: Implement network segmentation to isolate Hyper-V hosts from untrusted networks and implement enhanced monitoring for suspicious hypervisor activity. Within 30 days: Develop and test a patching strategy for deployment immediately when vendor patch becomes available; consider temporary workload migration to non-affected infrastructure if operationally feasible.

Windows CVE-2026-21255

HIGH

Improper Access Control (CWE-284)

2026-02-10 secure@microsoft.com

Windows Hyper-V Windows 10 1607 Windows 11 25h2 Windows Server 2022 Windows 10 22h2 Windows Server 2016 Windows 10 21h2 Windows 11 24h2 Windows 10 1809 Windows 11 23h2 Windows Server 2019 Windows Server 2022 23h2 Windows Server 2025 Microsoft

8.8

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

8.8 HIGH

AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Local

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Analysis Generated

Mar 12, 2026 - 22:02 vuln.today

CVE Published

Feb 10, 2026 - 18:16 nvd

HIGH 8.8

DescriptionCVE.org

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

AnalysisAI

Windows Hyper-V fails to properly enforce access controls, enabling local authenticated users to circumvent security features and gain unauthorized system access. This high-severity flaw affects Windows 10, Windows 11, Windows Server 2022, and Hyper-V implementations, allowing privileged attackers to escalate privileges across system boundaries. No patch is currently available for this vulnerability.

Technical ContextAI

Classified as CWE-284 (Improper Access Control). Affects Windows 10 1607. Improper access control in Windows Hyper-V allows an authorized attacker to bypass a security feature locally.

RemediationAI

Monitor vendor advisories for a patch.

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Same weakness CWE-284 – Improper Access Control

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CVE-2026-21255 vulnerability details – vuln.today

Back

Windows CVE-2026-21255

Severity by source

CVSS VectorNVD

Lifecycle Timeline

DescriptionCVE.org

AnalysisAI

Technical ContextAI

RemediationAI

More in Windows

Same weakness CWE-284 – Improper Access Control

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External POC / Exploit Code