IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2020-1027|Auth: low — authenticated user|Reboot: required|Manual only

KB4549949: Windows Server Security Update (April 2020)

An elevation of privilege vulnerability exists in the way that the Windows Kernel handles objects in memory. An attacker who successfully exploited the vulnerability could execute code with elevated permissions.

Published Apr 15, 2020 · Updated May 16, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A local attacker, with a low-privilege account, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2022-06-13 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Out-of-bounds Write (CWE-787) vulnerability in Microsoft Windows. An elevation of privilege vulnerability exists in the way that the Windows Kernel handles objects in memory, aka 'Windows Kernel Elevation of Privilege Vulnerability'. This CVE ID is unique from CVE-2020-0913, CVE-2020-1000, CVE-2020-1003. Exploitation requires local access, low attack complexity, a low-privilege authenticated account, and no user interaction required.

Am I affected?Quick check

Probably yes if any of these apply:

●Windows Administrators
●Systems Engineers
●IT Security
●Running windows 10 1507: -; windows 10 1607: -; windows 10 1709: -; windows 10 1803: -; windows 10 1809: -; windows 10 1903: -; windows 10 1909: -; windows 7: -; windows 8.1: -; windows rt 8.1: -; windows server 1803: -; windows server 1903: -; windows server 1909: -; windows server 2008: -, r2; windows server 2012: -, r2; windows server 2016: -; windows server 2019: -
Fixed inKB4549949, KB4549951, KB4550917, KB4550922, KB4550927, KB4550929, KB4550930, KB4550951, KB4550957, KB4550961, KB4550964, KB4550965, KB4550970, KB4550971 (applies to 41 product versions)
Real-world incidentsWhat we've seen

Active exploitation documented in the wild. Threat-research write-up: http://packetstormsecurity.com/files/168068/Windows-sxs-CNodeFactory-XMLParser_Element_doc_assembly_assemblyIdentity-Heap-Buffer-Overflow.html

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 CatalogKB4549949

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB4549949 — https://support.microsoft.com/help/4549949
    1
    KB4549951 — https://support.microsoft.com/help/4549951
    1
    KB4550917 — https://support.microsoft.com/help/4550917
    1
    KB4550922 — https://support.microsoft.com/help/4550922
    1
    KB4550927 — https://support.microsoft.com/help/4550927
    1
    KB4550929 — https://support.microsoft.com/help/4550929
    1
    KB4550930 — https://support.microsoft.com/help/4550930
    1
    KB4550951 — https://support.microsoft.com/help/4550951
    1
    KB4550957 — https://support.microsoft.com/help/4550957
    1
    KB4550961 — https://support.microsoft.com/help/4550961
    1
    KB4550964 — https://support.microsoft.com/help/4550964
    1
    KB4550965 — https://support.microsoft.com/help/4550965
    1
    KB4550970 — https://support.microsoft.com/help/4550970
    1
    KB4550971 — https://support.microsoft.com/help/4550971

Supersedes: KB4538461, KB4540670, KB4540673, KB4540681, KB4540688, KB4540689, KB4540693, KB4541506, KB4541509, KB4541510

Affected Products

    1
    Windows 10 Version 1607 for 32-bit Systems
    1
    Windows 10 Version 1607 for x64-based Systems
    1
    Windows 10 Version 1709 for 32-bit Systems
    1
    Windows 10 Version 1709 for ARM64-based Systems
    1
    Windows 10 Version 1709 for x64-based Systems
    1
    Windows 10 Version 1803 for 32-bit Systems
    1
    Windows 10 Version 1803 for ARM64-based Systems
    1
    Windows 10 Version 1803 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 1903 for 32-bit Systems
    1
    Windows 10 Version 1903 for ARM64-based Systems
    1
    Windows 10 Version 1903 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 for 32-bit Systems
    1
    Windows 10 for x64-based Systems
    1
    Windows 7 for 32-bit Systems Service Pack 1
    1
    (…21 more product versions)

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 KB4549949
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 KB4549949 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4549949
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4549951
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4550917
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4550922
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4550927
    1
    (…9 more)

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB4549949','KB4549951','KB4550917','KB4550922','KB4550927','KB4550929','KB4550930','KB4550951','KB4550957','KB4550961','KB4550964','KB4550965','KB4550970','KB4550971') }

References

    1
    Microsoft Security Response Center: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1027
    1
    KB article: https://support.microsoft.com/help/4549949
    1
    KB article: https://support.microsoft.com/help/4550917
    1
    KB article: https://support.microsoft.com/help/4550922
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2020-1027
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-1027

Discovery Credit

Google: Project Zero and Threat Analysis Group

PowerShell automationComing soon

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

References

↗ CVE-2020-1027↗ MSRC Advisory↗ NVD↗ KBKB4549949