{"cve":"CVE-2021-43890","nvd":{"published":"2021-12-15T15:15:11.207","modified":"2026-08-06T05:16:36.653","status":"Analyzed","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.\nAn 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.\nPlease 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.\nPlease see the Mitigations and Workaround sections for important information about steps you can take to protect your system from this vulnerability.\nDecember 27 2023 Update:\nIn 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.\nTo address this increase in activity, we have updated the App Installer to disable the ms-appinstaller protocol by default and recommend other potential mitigations.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H","score":7.1},"cwes":[],"references":["https://github.com/ChrisTitusTech/winutil/pull/26","https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890","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/"],"products":["microsoft:app_installer"],"source":"nvd","synced_at":"2026-10-19T21:25:41.256909649+00:00"},"epss":{"cve":"CVE-2021-43890","score":0.11294,"percentile":0.95974,"date":"2026-10-31"},"kev":{"cve":"CVE-2021-43890","date_added":"2021-12-15","due_date":"2021-12-29","vendor":"Microsoft","product":"Windows","known_ransomware":true},"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}