IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2021-38646|Auth: none — unauthenticated|Reboot: required|Manual only

KB5001958: Windows Server Security Update (September 2021)

Microsoft Office Access Connectivity Engine contains an unspecified vulnerability which can allow for remote code execution.

Published Sep 15, 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. CISA has confirmed use of this vulnerability in known ransomware campaigns — treat as high priority for remediation. Federal agencies are required to remediate by 2022-04-18 under CISA BOD 22-01.

How the attack worksNo clicks needed

This vulnerability affects Microsoft Office. 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: -; office: 2013, 2016, 2019
Fixed inKB5001958, KB5001997 (applies to 9 product versions) — build 5215.1000, 5381.1000+
Real-world incidentsWhat we've seen

CISA confirms this CVE has been used in known ransomware campaigns. Added to the KEV catalog on 2022-03-28; federal agencies required to remediate by 2022-04-18.

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 CatalogKB5001958

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB5001958 — https://support.microsoft.com/help/5001958
    1
    KB5001997 — https://support.microsoft.com/help/5001997

Supersedes: KB4493197, KB4493206

Affected Products

    1
    Microsoft 365 Apps for Enterprise for 32-bit Systems
    1
    Microsoft 365 Apps for Enterprise for 64-bit Systems
    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

Fixed Build Numbers

    1
    5215.1000
    1
    5381.1000
    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 KB5001958
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 KB5001958 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://www.microsoft.com/downloads/details.aspx?familyid=41f28314-646f-4e17-829e-2bfdd3e94f56
    1
    https://www.microsoft.com/downloads/details.aspx?familyid=5fc41c1d-ca0d-4250-907e-1e9e55498c05
    1
    https://www.microsoft.com/downloads/details.aspx?familyid=c94f1c97-6583-458d-bfe3-5fa0e424b5b9
    1
    https://www.microsoft.com/downloads/details.aspx?familyid=fa7826f4-771f-4c30-9a8a-a663d4f9d098

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB5001958','KB5001997') }

References

    1
    Microsoft Security Response Center: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-38646
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2021-38646
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-38646

Discovery Credit

Eugene Lim with Government Technology Agency of Singapore

PowerShell automationComing soon

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

References

↗ CVE-2021-38646↗ MSRC Advisory↗ NVD↗ KBKB5001958