IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2019-0841|Auth: low — authenticated user|Reboot: required|Manual only

KB4493441: Windows Server Security Update (April 2019)

A privilege escalation vulnerability exists when Windows AppXSVC improperly handles hard links. An attacker who successfully exploited this vulnerability could run processes in an elevated context.

Published Apr 9, 2019 · 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. CISA has confirmed use of this vulnerability in known ransomware campaigns — treat as high priority for remediation. Federal agencies are required to remediate by 2022-04-05 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 Windows AppX Deployment Service (AppXSVC) improperly handles hard links, aka 'Windows Elevation of Privilege Vulnerability'. This CVE ID is unique from CVE-2019-0730, CVE-2019-0731, CVE-2019-0796, CVE-2019-0805, CVE-2019-0836. 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 server 2016: 1803; windows server 2019: -
Fixed inKB4493441, KB4493464, KB4493474, KB4493509 (applies to 15 product versions)
Real-world incidentsWhat we've seen

Used in known ransomware campaigns. Threat-research write-up: http://packetstormsecurity.com/files/153642/AppXSvc-Hard-Link-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 CatalogKB4493441

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB4493441 — https://support.microsoft.com/help/4493441
    1
    KB4493464 — https://support.microsoft.com/help/4493464
    1
    KB4493474 — https://support.microsoft.com/help/4493474
    1
    KB4493509 — https://support.microsoft.com/help/4493509

Supersedes: KB4489868, KB4489871, KB4489886, KB4489899

Affected Products

    1
    Windows 10 Version 1703 for 32-bit Systems
    1
    Windows 10 Version 1703 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 Server 2019
    1
    Windows Server 2019 (Server Core installation)
    1
    Windows Server, version 1709 (Server Core Installation)
    1
    Windows Server, version 1803 (Server Core Installation)

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 KB4493441
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 KB4493441 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4493441
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4493464
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4493474
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4493509

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB4493441','KB4493464','KB4493474','KB4493509') }

References

    1
    Microsoft Security Response Center: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-0841
    1
    KB article: https://support.microsoft.com/help/4493441
    1
    KB article: https://support.microsoft.com/help/4493464
    1
    KB article: https://support.microsoft.com/help/4493474
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2019-0841
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-0841

Discovery Credit

Wenxu Wu (@ma7h1as) of Tencent Security Xuanwu Lab, Nabeel Ahmed of Dimension Data Belgium, Anonymous working with Trend Micro's Zero Day Initiative, ShiQin of Tencent Security Xuanwu Lab

PowerShell automationComing soon

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

References

↗ CVE-2019-0841↗ MSRC Advisory↗ NVD↗ KBKB4493441