CVE-2021-43890: Microsoft Windows AppX Installer Spoofing Vulnerability
First published: Tue Dec 14 2021(Updated: )
<p>We have investigated reports of a spoofing vulnerability in AppX installer that affects Microsoft Windows. Microsoft is aware of attacks that attempt to exploit this vulnerability by using specially crafted packages that include the malware family known as Emotet/Trickbot/Bazaloader.</p> <p>An attacker could craft a malicious attachment to be used in phishing campaigns. The attacker would then have to convince the user to open the specially crafted attachment. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.</p> <p>Please see the <strong>Security Updates</strong> table for the link to the updated app. Alternatively you can download and install the Installer using the links provided in the <strong>FAQ</strong> section.</p> <p>Please see the <strong>Mitigations</strong> and <strong>Workaround</strong> sections for important information about steps you can take to protect your system from this vulnerability.</p> <p><strong>December 27 2023 Update:</strong></p> <p>In recent months, Microsoft Threat Intelligence has seen an increase in activity from threat actors leveraging social engineering and phishing techniques to target Windows OS users and utilizing the <a href="https://learn.microsoft.com/en-us/windows/msix/app-installer/installing-windows10-apps-web">ms-appinstaller URI scheme</a>.</p> <p>To address this increase in activity, we have updated the App Installer to disable the ms-appinstaller protocol by default and recommend other potential mitigations.</p>
Credit: secure@microsoft.com secure@microsoft.com secure@microsoft.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Microsoft App Installer | ||
| Microsoft Windows 10 | ||
| Microsoft Windows 10 | ||
| Microsoft Windows AppX Installer | =Unknown | |
| Microsoft App Installer | =1.18.2691 | |
| Microsoft App Installer | ||
| All of | ||
| Microsoft App Installer | <1.16 | |
| Any of | ||
| Microsoft Windows 10 1809 | ||
| Microsoft Windows 10 1903 | ||
| Microsoft Windows 10 1909 | ||
| Microsoft Windows 10 2004 | ||
| Microsoft Windows 10 20h2 | ||
| Microsoft Windows 10 21h1 | ||
| Microsoft Windows 10 21h2 | ||
| Microsoft Windows 11 21h2 | ||
| All of | ||
| Microsoft App Installer | <1.11 | |
| Any of | ||
| Microsoft Windows 10 1507 | ||
| Microsoft Windows 10 1709 | ||
| Microsoft Windows 10 1803 | ||
| Microsoft Windows | ||
| All of | ||
| <1.16 | ||
| Any of | ||
| All of | ||
| <1.11 | ||
| Any of | ||
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Reference Links
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-43890 (Advisory)
- https://www.theregister.com/2024/01/04/microsoft_windows_app_installation/
- https://github.com/ChrisTitusTech/winutil/pull/26
- https://thehackernews.com/2023/12/microsoft-disables-msix-app-installer.html
- https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-msix-protocol-handler-abused-in-malware-attacks/
- https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/
- https://nvd.nist.gov/vuln/detail/CVE-2021-43890
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