IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2024-21338|Auth: low — authenticated user|Reboot: required|Manual only

KB5034763: Windows Server Security Update (February 2024)

Microsoft Windows Kernel contains an exposed IOCTL with insufficient access control vulnerability within the IOCTL (input and output control) dispatcher in appid.sys that allows a local attacker to achieve privilege escalation.

Published Feb 13, 2024 · 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. CISA has confirmed use of this vulnerability in known ransomware campaigns — treat as high priority for remediation. Federal agencies are required to remediate by 2024-03-25 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Software Vulnerability (CWE-822) (CWE-822) vulnerability in Microsoft Windows. Windows Kernel 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 1809: v < 10.0.17763.5458; windows 10 21h2: v < 10.0.19044.4046; windows 10 22h2: v < 10.0.19045.4046; windows 11 21h2: v < 10.0.22000.2777; windows 11 22h2: v < 10.0.22621.3155; windows 11 23h2: v < 10.0.22631.3155; windows server 2019: v < 10.0.17763.5458; windows server 2022: v < 10.0.20348.2322; windows server 2022 23h2: v ≤ 10.0.25398.709
Fixed inKB5034763, KB5034765, KB5034766, KB5034768, KB5034769, KB5034770 (applies to 20 product versions) — build 10.0.17763.5458, 10.0.19044.4046+
Real-world incidentsWhat we've seen

Used in known ransomware campaigns. Threat-research write-up: https://decoded.avast.io/janvojtesek/lazarus-and-the-fudmodule-rootkit-beyond-byovd-with-an-admin-to-kernel-zero-day/

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 CatalogKB5034763

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB5034763 — https://support.microsoft.com/help/5034763
    1
    KB5034765 — https://support.microsoft.com/help/5034765
    1
    KB5034766 — https://support.microsoft.com/help/5034766
    1
    KB5034768 — https://support.microsoft.com/help/5034768
    1
    KB5034769 — https://support.microsoft.com/help/5034769
    1
    KB5034770 — https://support.microsoft.com/help/5034770

Supersedes: KB5034121, KB5034122, KB5034123, KB5034127, KB5034129, KB5034130

Affected Products

    1
    Windows 10 Version 1809 for 32-bit Systems
    1
    Windows 10 Version 1809 for ARM64-based Systems
    1
    Windows 10 Version 1809 for x64-based Systems
    1
    Windows 10 Version 21H2 for 32-bit Systems
    1
    Windows 10 Version 21H2 for ARM64-based Systems
    1
    Windows 10 Version 21H2 for x64-based Systems
    1
    Windows 10 Version 22H2 for 32-bit Systems
    1
    Windows 10 Version 22H2 for ARM64-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 21H2 for ARM64-based Systems
    1
    Windows 11 version 21H2 for x64-based Systems
    1
    Windows Server 2019
    1
    Windows Server 2019 (Server Core installation)
    1
    Windows Server 2022
    1
    Windows Server 2022 (Server Core installation)
    1
    Windows Server 2022, 23H2 Edition (Server Core installation)

Fixed Build Numbers

    1
    10.0.17763.5458
    1
    10.0.19044.4046
    1
    10.0.19045.4046
    1
    10.0.20348.2322
    1
    10.0.22000.2777
    1
    10.0.22621.3155
    1
    10.0.22631.3155
    1
    10.0.25398.709

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 KB5034763
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 KB5034763 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5034763
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5034765
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5034766
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5034768
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5034769
    1
    (…1 more)

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB5034763','KB5034765','KB5034766','KB5034768','KB5034769','KB5034770') }

References

    1
    Microsoft Security Response Center: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2024-21338
    1
    KB article: https://support.microsoft.com/help/5034763
    1
    KB article: https://support.microsoft.com/help/5034765
    1
    KB article: https://support.microsoft.com/help/5034766
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2024-21338
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2024-21338

Discovery Credit

Jan Vojtěšek with Avast

PowerShell automationComing soon

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

References

↗ CVE-2024-21338↗ MSRC Advisory↗ NVD↗ KBKB5034763