IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2021-42292|Auth: none — unauthenticated|Reboot: required|Manual only

KB4486670: Windows Server Security Update (November 2021)

A security feature bypass vulnerability in Microsoft Excel would allow a local user to perform arbitrary code execution.

Published Nov 10, 2021 · Updated May 16, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A local attacker, without authentication, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2021-12-01 under CISA BOD 22-01.

How the attack worksNo clicks needed

This vulnerability affects Microsoft Office. Microsoft Excel Security Feature Bypass Vulnerability Exploitation requires local access, low attack complexity, no authentication required, and user interaction required.

Am I affected?Quick check

Probably yes if any of these apply:

●IT Security
●Running 365 apps: -; excel: 2013; office: 2013, 2016, 2019; office long term servicing channel: 2021
Fixed inKB4486670, KB5002035, KB5002056, KB5002072 (applies to 18 product versions) — build 15.0.5397.1001, 16.0.5239.1001+
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2021-11-17 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2021-12-01.

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 CatalogKB4486670

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB4486670 — https://support.microsoft.com/help/4486670
    1
    KB5002035 — https://support.microsoft.com/help/5002035
    1
    KB5002056 — https://support.microsoft.com/help/5002056
    1
    KB5002072 — https://support.microsoft.com/help/5002072

Supersedes: KB4475514, KB5002007, KB5002030, KB5002043

Affected Products

    1
    Microsoft 365 Apps for Enterprise for 32-bit Systems
    1
    Microsoft 365 Apps for Enterprise for 64-bit Systems
    1
    Microsoft Excel 2013 RT Service Pack 1
    1
    Microsoft Excel 2013 Service Pack 1 (32-bit editions)
    1
    Microsoft Excel 2013 Service Pack 1 (64-bit editions)
    1
    Microsoft Excel 2016 (32-bit edition)
    1
    Microsoft Excel 2016 (64-bit edition)
    1
    Microsoft Office 2013 RT Service Pack 1
    1
    Microsoft Office 2013 Service Pack 1 (32-bit editions)
    1
    Microsoft Office 2013 Service Pack 1 (64-bit editions)
    1
    Microsoft Office 2016 (32-bit edition)
    1
    Microsoft Office 2016 (64-bit edition)
    1
    Microsoft Office 2019 for 32-bit editions
    1
    Microsoft Office 2019 for 64-bit editions
    1
    Microsoft Office 2019 for Mac
    1
    Microsoft Office LTSC 2021 for 32-bit editions
    1
    Microsoft Office LTSC 2021 for 64-bit editions
    1
    Microsoft Office LTSC for Mac 2021

Fixed Build Numbers

    1
    15.0.5397.1001
    1
    16.0.5239.1001
    1
    16.55.21111400
    1
    https://aka.ms/OfficeSecurityReleases

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 (may or may not be required for this update)

Microsoft Update Catalog (manual download)

1
Open https://catalog.update.microsoft.com
2
Search for KB4486670
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 KB4486670 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://go.microsoft.com/fwlink/p/?linkid=831049
    1
    https://www.microsoft.com/download/details.aspx?familyid=0ec80d86-bf94-4736-8588-1bd13f3006c2
    1
    https://www.microsoft.com/download/details.aspx?familyid=20805cdc-42a5-49ce-8c8e-61ae13820adc
    1
    https://www.microsoft.com/download/details.aspx?familyid=28ed4be7-dc7f-41aa-9bd3-ba9fb4e01842
    1
    https://www.microsoft.com/download/details.aspx?familyid=67963ad4-3c22-49eb-8fa8-d6a7ea30b6ff
    1
    (…4 more)

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB4486670','KB5002035','KB5002056','KB5002072') }

References

    1
    Microsoft Security Response Center: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42292
    1
    KB article: https://support.microsoft.com/help/4486670
    1
    KB article: https://support.microsoft.com/help/5002035
    1
    KB article: https://support.microsoft.com/help/5002056
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2021-42292
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42292

Discovery Credit

MSTIC

PowerShell automationComing soon

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

References

↗ CVE-2021-42292↗ MSRC Advisory↗ NVD↗ KBKB4486670