IRONSMITHINTEL
HIGHCVSS8.8
|
Actively Exploited
|CISA KEV|CVE-2021-27085|Auth: none — unauthenticated|Reboot: required|Manual only

KB5000802: Windows Server Security Update (March 2021)

Microsoft Internet Explorer contains an unspecified vulnerability that allows for remote code execution.

Published Mar 11, 2021 · Updated May 16, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

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

How the attack worksNo clicks needed

This vulnerability affects Microsoft Internet Explorer. Internet Explorer Remote Code Execution Vulnerability Exploitation requires remote network access, low 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:

●IT Security
●Running internet explorer: 11
Fixed inKB5000802, KB5000808, KB5000809, KB5000822 (applies to 16 product versions)
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 CatalogKB5000802

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB5000802 — https://support.microsoft.com/help/5000802
    1
    KB5000808 — https://support.microsoft.com/help/5000808
    1
    KB5000809 — https://support.microsoft.com/help/5000809
    1
    KB5000822 — https://support.microsoft.com/help/5000822

Supersedes: KB4601315, KB4601319, KB4601345, KB4601354

Affected Products

    1
    Internet Explorer 11 on Windows 10 Version 1803 for 32-bit Systems
    1
    Internet Explorer 11 on Windows 10 Version 1803 for ARM64-based Systems
    1
    Internet Explorer 11 on Windows 10 Version 1803 for x64-based Systems
    1
    Internet Explorer 11 on Windows 10 Version 1809 for 32-bit Systems
    1
    Internet Explorer 11 on Windows 10 Version 1809 for ARM64-based Systems
    1
    Internet Explorer 11 on Windows 10 Version 1809 for x64-based Systems
    1
    Internet Explorer 11 on Windows 10 Version 1909 for 32-bit Systems
    1
    Internet Explorer 11 on Windows 10 Version 1909 for ARM64-based Systems
    1
    Internet Explorer 11 on Windows 10 Version 1909 for x64-based Systems
    1
    Internet Explorer 11 on Windows 10 Version 2004 for 32-bit Systems
    1
    Internet Explorer 11 on Windows 10 Version 2004 for ARM64-based Systems
    1
    Internet Explorer 11 on Windows 10 Version 2004 for x64-based Systems
    1
    Internet Explorer 11 on Windows 10 Version 20H2 for 32-bit Systems
    1
    Internet Explorer 11 on Windows 10 Version 20H2 for ARM64-based Systems
    1
    Internet Explorer 11 on Windows 10 Version 20H2 for x64-based Systems
    1
    Internet Explorer 11 on Windows Server 2019

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 KB5000802
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 KB5000802 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5000802
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5000808
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5000809
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5000822

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB5000802','KB5000808','KB5000809','KB5000822') }

References

    1
    Microsoft Security Response Center: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-27085
    1
    KB article: https://support.microsoft.com/help/5000802
    1
    KB article: https://support.microsoft.com/help/5000808
    1
    KB article: https://support.microsoft.com/help/5000822
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2021-27085
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27085

Discovery Credit

Chi-Yu You and Dhanesh Kizhakkinan of FireEye Inc.

PowerShell automationComing soon

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

References

↗ CVE-2021-27085↗ MSRC Advisory↗ NVD↗ KBKB5000802