IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2025-21334|Auth: low — authenticated user|Reboot: required|Manual only

KB5049981: Windows Server Security Update (January 2025)

Microsoft Windows Hyper-V NT Kernel Integration VSP contains a use-after-free vulnerability that allows a local attacker to gain SYSTEM privileges.

Published Jan 14, 2025 · Updated May 16, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A local attacker, with a low-privilege account, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2025-02-04 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Use After Free (CWE-416) vulnerability in Microsoft Windows. Windows Hyper-V NT Kernel Integration VSP Elevation of Privilege Vulnerability Exploitation requires local access, low attack complexity, a low-privilege authenticated account, and no user interaction required.

Am I affected?Quick check

Probably yes if any of these apply:

●Windows Administrators
●Systems Engineers
●IT Security
●Running windows 10 21h2: v < 10.0.19044.5371; windows 10 22h2: v < 10.0.19045.5371; windows 11 22h2: v < 10.0.22621.4751; windows 11 23h2: v < 10.0.22631.4751; windows 11 24h2: v < 10.0.26100.2894; windows server 2022 23h2: v < 10.0.25398.1369; windows server 2025: v < 10.0.26100.2894
Fixed inKB5049981, KB5049984, KB5050009, KB5050021 (applies to 11 product versions) — build 10.0.19044.5371, 10.0.19045.5371+
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2025-01-14 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2025-02-04.

How to patch

Manual download

For air-gapped servers or out-of-band deployment. Microsoft Update Catalog returns every OS-version variant of this update.

↗ Microsoft Update CatalogKB5049981

Manual remediation steps

Apply the Microsoft Security Update

Microsoft has released an official security update that fixes this vulnerability.

Required KB Updates

    1
    KB5049981 — https://support.microsoft.com/help/5049981
    1
    KB5049984 — https://support.microsoft.com/help/5049984
    1
    KB5050009 — https://support.microsoft.com/help/5050009
    1
    KB5050021 — https://support.microsoft.com/help/5050021

Supersedes: KB5048652, KB5048653, KB5048667, KB5048685

Affected Products

    1
    Windows 10 Version 21H2 for x64-based Systems
    1
    Windows 10 Version 22H2 for x64-based Systems
    1
    Windows 11 Version 22H2 for ARM64-based Systems
    1
    Windows 11 Version 22H2 for x64-based Systems
    1
    Windows 11 Version 23H2 for ARM64-based Systems
    1
    Windows 11 Version 23H2 for x64-based Systems
    1
    Windows 11 Version 24H2 for ARM64-based Systems
    1
    Windows 11 Version 24H2 for x64-based Systems
    1
    Windows Server 2022, 23H2 Edition (Server Core installation)
    1
    Windows Server 2025
    1
    Windows Server 2025 (Server Core installation)

Fixed Build Numbers

    1
    10.0.19044.5371
    1
    10.0.19045.5371
    1
    10.0.22621.4751
    1
    10.0.22631.4751
    1
    10.0.25398.1369
    1
    10.0.26100.2894

Installation Methods

Windows Update (recommended)

1
Settings → Windows Update → Check for updates
2
The security update is offered if your system is in scope
3
Restart when prompted — a reboot IS required to complete the install

Microsoft Update Catalog (manual download)

1
Open https://catalog.update.microsoft.com
2
Search for KB5049981
3
Download the package matching your OS architecture and Windows build
4
Run the .msu installer with administrator privileges
5
Restart when prompted

WSUS / SCCM / Intune

Approve KB5049981 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5049981
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5049984
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5050009
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5050021

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB5049981','KB5049984','KB5050009','KB5050021') }

References

    1
    Microsoft Security Response Center: https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2025-21334
    1
    KB article: https://support.microsoft.com/help/5049981
    1
    KB article: https://support.microsoft.com/help/5049984
    1
    KB article: https://support.microsoft.com/help/5050009
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2025-21334
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-21334
PowerShell automationComing soon

No tested PowerShell script for this entry yet. We’re prioritising automation based on user demand.

References

↗ CVE-2025-21334↗ MSRC Advisory↗ NVD↗ KBKB5049981