IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2020-0787|Auth: none — unauthenticated|Reboot: required|Manual only

KB4538461: Windows Server Security Update (March 2020)

Microsoft Windows BITS is vulnerable to to a privilege elevation vulnerability if it improperly handles symbolic links. An actor can exploit this vulnerability to execute arbitrary code with system-level privileges.

Published Mar 12, 2020 · 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 2022-07-28 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Software Vulnerability (CWE-59) (CWE-59) vulnerability in Microsoft Windows. An elevation of privilege vulnerability exists when the Windows Background Intelligent Transfer Service (BITS) improperly handles symbolic links, aka 'Windows Background Intelligent Transfer Service Elevation of Privilege 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:

●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 inKB4538461, KB4540670, KB4540673, KB4540681, KB4540688, KB4540689, KB4540693, KB4540694, KB4541500, KB4541504, KB4541505, KB4541506, KB4541509, KB4541510 (applies to 41 product versions)
Real-world incidentsWhat we've seen

Used in known ransomware campaigns. Threat-research write-up: http://packetstormsecurity.com/files/158056/Background-Intelligent-Transfer-Service-Privilege-Escalation.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 CatalogKB4538461

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB4538461 — https://support.microsoft.com/help/4538461
    1
    KB4540670 — https://support.microsoft.com/help/4540670
    1
    KB4540673 — https://support.microsoft.com/help/4540673
    1
    KB4540681 — https://support.microsoft.com/help/4540681
    1
    KB4540688 — https://support.microsoft.com/help/4540688
    1
    KB4540689 — https://support.microsoft.com/help/4540689
    1
    KB4540693 — https://support.microsoft.com/help/4540693
    1
    KB4540694 — https://support.microsoft.com/help/4540694
    1
    KB4541500 — https://support.microsoft.com/help/4541500
    1
    KB4541504 — https://support.microsoft.com/help/4541504
    1
    KB4541505 — https://support.microsoft.com/help/4541505
    1
    KB4541506 — https://support.microsoft.com/help/4541506
    1
    KB4541509 — https://support.microsoft.com/help/4541509
    1
    KB4541510 — https://support.microsoft.com/help/4541510

Supersedes: KB4532691, KB4532693, KB4537762, KB4537764, KB4537776, KB4537789, KB4537810, KB4537814, KB4537820, KB4537821

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 KB4538461
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 KB4538461 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4538461
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4540670
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4540673
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4540681
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4540688
    1
    (…9 more)

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB4538461','KB4540670','KB4540673','KB4540681','KB4540688','KB4540689','KB4540693','KB4540694','KB4541500','KB4541504','KB4541505','KB4541506','KB4541509','KB4541510') }

References

    1
    Microsoft Security Response Center: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0787
    1
    KB article: https://support.microsoft.com/help/4538461
    1
    KB article: https://support.microsoft.com/help/4540670
    1
    KB article: https://support.microsoft.com/help/4540673
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2020-0787
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-0787

Discovery Credit

Clément Labro (@itm4n), Jarvis_1oop of Pinduoduo Security Research Lab

PowerShell automationComing soon

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

References

↗ CVE-2020-0787↗ MSRC Advisory↗ NVD↗ KBKB4538461