Microsoft Windows AppX Installer Spoofing Vulnerability

[ Why it matters ]Priority signals

• Exploited in the wild: on CISA's Known Exploited Vulnerabilities list since 2021-12-15
• Known to be used in ransomware campaigns
• EPSS: 11% chance of exploitation in the next 30 days (higher than 96% of CVEs)

[ Description ]Official description

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. 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. Please see the Security Updates table for the link to the updated app. Alternatively you can download and install the Installer using the links provided in the FAQ section. Please see the Mitigations and Workaround sections for important information about steps you can take to protect your system from this vulnerability. December 27 2023 Update: 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 ms-appinstaller URI scheme. 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.

CISA: Microsoft Windows AppX Installer contains a spoofing vulnerability which has a high impacts to confidentiality, integrity, and availability.

[ Fixes ]Fixes and patches

CISA required action (US federal deadline 29 Dec 2021): Apply updates per vendor instructions.

• Patch on portal.msrc.microsoft.comVendor patch or bulletin · NVD · Reference tagged 'Patch' by NVD

[ References ]References

• github.com/ChrisTitusTech/winutil/pull/26Issue Tracking
• portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890PatchVendor Advisory
• thehackernews.com/2023/12/microsoft-disables-msix-app-installer.htmlPress/Media CoverageThird Party Advisory
• www.bleepingcomputer.com/news/microsoft/microsoft-disables-msix-protocol-handler-abused…Press/Media CoverageThird Party Advisory
• www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-mi…ExploitVendor Advisory
• www.cisa.gov/known-exploited-vulnerabilities-catalogUS Government Resource