High

Windows Hyper-V Security Feature Bypass Vulnerability

IdentifiersCVE-2026-21255CWE-284· Improper Access Control

CVE-2026-21255 is an improper access control vulnerability in Windows Hyper-V. According to the provided content, the flaw allows an authorized attacker to bypass a security feature through local exploitation. The available metadata identifies the weakness as CWE-284 and gives a CVSS v3.1 vector of AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H, indicating a low-complexity local attack requiring low privileges and no user interaction. No additional technical detail about the specific Hyper-V function, code path, or security boundary being bypassed is provided in the supplied material.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows a locally authenticated or otherwise authorized attacker to bypass a security feature in Windows Hyper-V. The supplied CVSS vector indicates scope change and high potential impact to confidentiality, integrity, and availability, suggesting that exploitation could undermine isolation or protections enforced by Hyper-V and lead to significant downstream security consequences. However, the precise post-bypass effects are not further described in the provided content.

Mitigation

If you can’t patch tonight, do this now.

No specific workaround or mitigation for CVE-2026-21255 is provided in the supplied content. In the absence of a vendor-provided mitigation, the practical mitigation is to restrict local access and low-privilege account use on Hyper-V hosts, minimize interactive/logon access to systems running Hyper-V, and prioritize patch deployment on affected systems.

Remediation

Patch, then assume compromise.

Microsoft released a security update for CVE-2026-21255 as part of its February 2026 security updates. Remediation is to apply the relevant Microsoft security patches for affected Windows versions and verify successful installation through Windows Update, Update History, or, if necessary, packages obtained from the Microsoft Update Catalog.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

Microsoft CorporationWindows 10 1607operating_system

Microsoft CorporationWindows 10 1809operating_system

Microsoft CorporationWindows 10 21h2operating_system

Microsoft CorporationWindows 10 22h2operating_system

Microsoft CorporationWindows 11 23h2operating_system

Microsoft CorporationWindows 11 24h2operating_system

Microsoft CorporationWindows 11 25h2operating_system

Microsoft CorporationWindows 11 26h1operating_system

Microsoft CorporationWindows Server 2016operating_system

Microsoft CorporationWindows Server 2019operating_system

Microsoft CorporationWindows Server 2022operating_system

Microsoft CorporationWindows Server 2022 23h2operating_system

Microsoft CorporationWindows Server 2025operating_system

Microsoft CorporationWindows Server 23h2operating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

10 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

10 SOURCESView more in app

nsfocus globalNews

Mar 4, 2026

Microsoft’s February Security Update of High-Risk Vulnerability Notice for Multiple Products - NSFOCUS, Inc., a global network and cyber security leader, protects enterprises and carriers from advanced cyber attacks.

A security feature bypass vulnerability affecting Windows Hyper-V.

thecyberexpress com vulnerabilitiesNews

Feb 11, 2026

Microsoft Patch Tuesday February 2026 Fixes 6 Zero-Days

A vulnerability affecting Windows Hyper-V; specific impact type not provided in the content.

cyber security newsNews

Feb 10, 2026

Microsoft Patch Tuesday February 2026 - 54 Vulnerabilities Fixed, Including 6 Zero-days

A security feature bypass vulnerability in Windows Hyper-V.

cvefeed high severityNews

Feb 10, 2026

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

A local security feature bypass in Windows Hyper-V caused by improper access control, allowing an authorized low-privilege attacker to bypass a security feature.

+2 more in the timeline

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity3

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-21255

NVD

nvd.nist.gov/vuln/detail/CVE-2026-21255

MITRE CWE · CWE-284

Improper Access Control

Vendor Advisory

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21255