See Susan Bradley's 18-Dec-2021 Tips for the Week – What About the AppX Vulnerability? and related discussion <here> in the AskWoody forum for more information. According to Microsoft's Windows AppX Installer Spoofing Vulnerability (CVE-2021-43890) this vulnerability affects Win 10 v1809 and higher and Win 11.
This Windows AppX Installer vulnerability has been used in targeted attacks, but you should be protected if this app was patched to v1.16.13405.0 on or around 14-Dec-2021. Go to Settings | Apps & Feature | App Installer | Advanced Options to see your current version number.
Note that this patch for the Windows AppX Installer is normally delivered by the Microsoft Store, so if you haven't received this v1.16.13405.0 update yet it might be because you have disabled automatic updating of installed UWP (Universal Windows Platform) apps in your Microsoft Store app. To check, launch the Microsoft Store app, click the icon for your account profile, and go to App Settings | App Updates - Update Apps Automatically. If you haven't received the update yet, you can also click the blue "Get Updates" button on the Library tab of the Microsoft Store to manually check for available updates for all your installed UWP apps.
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Dell Inspiron 5584 * 64-bit Win 10 Pro v21H1 build 19043.1415 * Firefox v95.0.2 * Microsoft Defender v.4.18.2111.5-1.1.18800.4 * Malwarebytes Premium v4.5.0.152-1.0.1538