Security News Microsoft disables MSIX protocol handler abused in malware attacks


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Apr 24, 2016
Microsoft has again disabled the MSIX ms-appinstaller protocol handler after multiple financially motivated threat groups abused it to infect Windows users with malware.

The attackers exploited the CVE-2021-43890 Windows AppX Installer spoofing vulnerability to circumvent security measures that would otherwise protect Windows users from malware, such as the Defender SmartScreen anti-phishing and anti-malware component and built-in browser alerts cautioning users against executable file downloads.

Microsoft says the threat actors use both malicious advertisements for popular software and Microsoft Teams phishing messages to push signed malicious MSIX application packages.

"Since mid-November 2023, Microsoft Threat Intelligence has observed threat actors, including financially motivated actors like Storm-0569, Storm-1113, Sangria Tempest, and Storm-1674, utilizing the ms-appinstaller URI scheme (App Installer) to distribute malware," the company said.
Today, Microsoft recommended installing the patched App Installer version 1.21.3421.0 or later to block exploitation attempts.


Level 18
Top Poster
May 4, 2019
Microsoft on Thursday said it's once again disabling the ms-appinstaller protocol handler by default following its abuse by multiple threat actors to distribute malware.
“The observed threat actor activity abuses the current implementation of the ms-appinstaller protocol handler as an access vector for malware that may lead to ransomware distribution,” the Microsoft Threat Intelligence team said.

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