IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2021-41357|Auth: low — authenticated user|Reboot: required|Manual only

KB5006670: Windows Server Security Update (October 2021)

Microsoft Win32k contains an unspecified vulnerability that allows for privilege escalation.

Published Oct 13, 2021 · 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 2022-05-16 under CISA BOD 22-01.

How the attack worksNo clicks needed

This vulnerability affects Microsoft Win32k. 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:

●IT Security
●Running windows 10 2004: v < 10.0.19041.1288; windows 10 20h2: v < 10.0.19042.1288; windows 10 21h1: v < 10.0.19043.1288; windows 11 21h2: v < 10.0.22000.258; windows server 2004: v < 10.0.19041.1288; windows server 2022: v < 10.0.20348.288; windows server 20h2: v < 10.0.19042.1288
Fixed inKB5006670, KB5006674, KB5006699 (applies to 14 product versions) — build 10.0.19041.1288, 10.0.19042.1288+
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2022-04-25 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2022-05-16.

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 CatalogKB5006670

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB5006670 — https://support.microsoft.com/help/5006670
    1
    KB5006674 — https://support.microsoft.com/help/5006674
    1
    KB5006699 — https://support.microsoft.com/help/5006699

Supersedes: KB5005565, KB5005575

Affected Products

    1
    Windows 10 Version 2004 for 32-bit Systems
    1
    Windows 10 Version 2004 for ARM64-based Systems
    1
    Windows 10 Version 2004 for x64-based Systems
    1
    Windows 10 Version 20H2 for 32-bit Systems
    1
    Windows 10 Version 20H2 for ARM64-based Systems
    1
    Windows 10 Version 21H1 for 32-bit Systems
    1
    Windows 10 Version 21H1 for ARM64-based Systems
    1
    Windows 10 Version 21H1 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 2022
    1
    Windows Server 2022 (Server Core installation)
    1
    Windows Server, version 2004 (Server Core installation)
    1
    Windows Server, version 20H2 (Server Core Installation)

Fixed Build Numbers

    1
    10.0.19041.1288
    1
    10.0.19042.1288
    1
    10.0.19043.1288
    1
    10.0.20348.288
    1
    10.0.22000.258

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 KB5006670
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 KB5006670 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5006670
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5006674
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5006699

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB5006670','KB5006674','KB5006699') }

References

    1
    Microsoft Security Response Center: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-41357
    1
    KB article: https://support.microsoft.com/help/5006670
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2021-41357
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-41357

Discovery Credit

Anonymous

PowerShell automationComing soon

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

References

↗ CVE-2021-41357↗ MSRC Advisory↗ NVD↗ KBKB5006670