Live › vulnerability › CVE-2021-43890
Go to dashboardMicrosoft Windows AppX Installer has a spoofing flaw that CISA lists as actively exploited, and ransomware use is tagged in the KEV entry. The sources say it has high impact on confidentiality, integrity and availability, but do not say exactly what a spoofed installer lets an attacker do.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 19:11 UTC, 3h before NVD. All times on this page are UTC.
Apply updates per vendor instructions.
| Product | Ecosystem | Affected | Fixed in |
|---|---|---|---|
| Microsoft Windows | vendor | – | – |
Unknown from the sources. In the analyst’s queue.
Apply the Microsoft security update for CVE-2021-43890 per vendor instructions, as CISA requires; the specific KB or build numbers are not in the sources.
Each row is the first time that source carried this signal. The analyst’s rows are its own findings.
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.
This page as .md · .json · in your agent: get_signal("CVE-2021-43890")
CISA KEV catalog, Creative Commons 0 · EPSS scores by FIRST, used with attribution · NVD data is provided by NIST and is public domain. Posts quoted belong to their authors.