IRONSMITHINTEL
MEDIUMCVSS6.8
|
Actively Exploited
|CISA KEV|CVE-2021-34448|Auth: none — unauthenticated|Reboot: required|Manual only

KB5004237: Windows Server Security Update (July 2021)

Microsoft Windows Scripting Engine contains an unspecified vulnerability that allows for memory corruption.

Published Jul 16, 2021 · Updated May 16, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A remote attacker, without authentication, can achieve full data confidentiality loss, arbitrary modification of data. Federal agencies are required to remediate by 2021-11-17 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Out-of-bounds Write (CWE-787) vulnerability in Microsoft Windows. Exploitation requires remote network access, higher attack complexity, no authentication required, and user interaction required.

📧

Phishing link

→

🖼

Malicious file

🔓

Server compromised

Am I affected?Quick check

Probably yes if any of these apply:

●Windows Administrators
●Systems Engineers
●IT Security
●Running windows 10 1507: v < 10.0.10240.19003; windows 10 1607: v < 10.0.14393.4530; windows 10 1809: v < 10.0.17763.2061; windows 10 1909: v < 10.0.18363.1679; windows 10 2004: v < 10.0.19041.1110; windows 10 20h2: v < 10.0.19042.1110; windows 10 21h1: v < 10.0.19043.1110; windows 7: -; windows 8.1: -; windows rt 8.1: -; windows server 2008: r2; windows server 2012: -, r2; windows server 2016: v < 10.0.14393.4530; windows server 2019: v < 10.0.17763.2061
Fixed inKB5004237, KB5004238, KB5004244, KB5004245, KB5004249, KB5004289, KB5004294, KB5004298, KB5005563 (applies to 29 product versions) — build 10.0.10240.19003, 10.0.14393.4530+
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2021-11-03 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2021-11-17.

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 CatalogKB5004237

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB5004237 — https://support.microsoft.com/help/5004237
    1
    KB5004238 — https://support.microsoft.com/help/5004238
    1
    KB5004244 — https://support.microsoft.com/help/5004244
    1
    KB5004245 — https://support.microsoft.com/help/5004245
    1
    KB5004249 — https://support.microsoft.com/help/5004249
    1
    KB5004289 — https://support.microsoft.com/help/5004289
    1
    KB5004294 — https://support.microsoft.com/help/5004294
    1
    KB5004298 — https://support.microsoft.com/help/5004298
    1
    KB5005563 — https://support.microsoft.com/help/5005563

Supersedes: KB5004945, KB5004946, KB5004947, KB5004948, KB5004950, KB5004953, KB5004954, KB5004956, KB5005036

Affected Products

    1
    Windows 10 Version 1607 for 32-bit Systems
    1
    Windows 10 Version 1607 for x64-based Systems
    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 1909 for 32-bit Systems
    1
    Windows 10 Version 1909 for ARM64-based Systems
    1
    Windows 10 Version 1909 for x64-based Systems
    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 20H2 for x64-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 10 for 32-bit Systems
    1
    Windows 10 for x64-based Systems
    1
    Windows 7 for 32-bit Systems Service Pack 1
    1
    (…9 more product versions)

Fixed Build Numbers

    1
    10.0.10240.19003
    1
    10.0.14393.4530
    1
    10.0.17763.2061
    1
    10.0.18363.1679
    1
    10.0.19041.1110
    1
    10.0.19042.1110
    1
    10.0.19043.1110
    1
    6.1.7601.25661
    1
    6.2.9200.23409
    1
    6.3.9600.20069
    1
    (…1 more builds)

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 KB5004237
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 KB5004237 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5004237
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5004238
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5004244
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5004245
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5004249
    1
    (…4 more)

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB5004237','KB5004238','KB5004244','KB5004245','KB5004249','KB5004289','KB5004294','KB5004298','KB5005563') }

References

    1
    Microsoft Security Response Center: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34448
    1
    KB article: https://support.microsoft.com/help/5004237
    1
    KB article: https://support.microsoft.com/help/5004238
    1
    KB article: https://support.microsoft.com/help/5004244
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2021-34448
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34448

Discovery Credit

yangkang(@dnpushme)&bianliang&wanggang&lihongfei&liujialei of 360 ATA

PowerShell automationComing soon

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

References

↗ CVE-2021-34448↗ MSRC Advisory↗ NVD↗ KBKB5004237