IRONSMITHINTEL
HIGHCVSS7.2
|
Actively Exploited
|CISA KEV|CVE-2021-31196|Auth: high — administrative privileges|Reboot: required|Manual only

KB5004778: Windows Server Security Update (July 2021)

Microsoft Exchange Server contains an information disclosure vulnerability that allows for remote code execution.

Published Jul 14, 2021 · Updated May 16, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A remote attacker, with administrative privileges, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2024-09-11 under CISA BOD 22-01.

How the attack worksNo clicks needed

This vulnerability affects Microsoft Exchange Server. Exploitation requires remote network access, low attack complexity, an administrative account, and no user interaction required.

Am I affected?Quick check

Probably yes if any of these apply:

●Exchange Administrators
●Messaging Team
●IT Security
●Running exchange server: 2013, 2016, 2019
Fixed inKB5004778, KB5004779, KB5004780 (applies to 5 product versions) — build 15.00.1497.023, 15.01.2242.012+
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2024-08-21 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2024-09-11.

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 CatalogKB5004778

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB5004778 — https://support.microsoft.com/help/5004778
    1
    KB5004779 — https://support.microsoft.com/help/5004779
    1
    KB5004780 — https://support.microsoft.com/help/5004780

Supersedes: KB5003435

Affected Products

    1
    Microsoft Exchange Server 2013 Cumulative Update 23
    1
    Microsoft Exchange Server 2016 Cumulative Update 20
    1
    Microsoft Exchange Server 2016 Cumulative Update 21
    1
    Microsoft Exchange Server 2019 Cumulative Update 10
    1
    Microsoft Exchange Server 2019 Cumulative Update 9

Fixed Build Numbers

    1
    15.00.1497.023
    1
    15.01.2242.012
    1
    15.01.2308.014
    1
    15.02.0858.015
    1
    15.02.0922.013

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 KB5004778
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 KB5004778 for the affected products in your update management console.

Microsoft Download Center Links

    1
    http://www.microsoft.com/download/details.aspx?familyid=07683b40-1608-437d-a90a-eb2683cb3092
    1
    http://www.microsoft.com/download/details.aspx?familyid=61d75c2f-8b98-4971-b22c-ebd114772d3d
    1
    http://www.microsoft.com/download/details.aspx?familyid=a78de9ec-af4e-4e31-be7d-17db9fc335db
    1
    http://www.microsoft.com/download/details.aspx?familyid=cae731a5-0d00-4f76-b2c6-84bd511e529f
    1
    http://www.microsoft.com/download/details.aspx?familyid=ccf40c19-2653-4b5c-b922-d6d09bbf1c3e

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB5004778','KB5004779','KB5004780') }

References

    1
    Microsoft Security Response Center: https://msrc.microsoft.com/update-guide/en-US/advisory/CVE-2021-31196
    1
    KB article: https://support.microsoft.com/help/5004778
    1
    KB article: https://support.microsoft.com/help/5004779
    1
    KB article: https://support.microsoft.com/help/5004780
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2021-31196
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31196

Discovery Credit

Orange Tsai (@orange_8361) with DEVCORE

PowerShell automationComing soon

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

References

↗ CVE-2021-31196↗ MSRC Advisory↗ NVD↗ KBKB5004778