--- title: "CVE-2021-43890: Windows AppX Installer Spoofing… | CubePath" description: "We have investigated reports of a spoofing vulnerability in AppX installer that affects Microsoft Windows. Microsoft is aware of attacks that attempt…" language: en source: https://cubepath.com/security/cve/CVE-2021-43890 --- # CVE-2021-43890: Windows AppX Installer Spoofing… | CubePath ## 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. Official description from the CVE record, published by microsoft. Copyright © 1999-2026 The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CVE license. [View the record on cve.org](https://www.cve.org/CVERecord?id=CVE-2021-43890) ## Key data ### CVSS 3.1 High 7.1 Score published by microsoft in the CVE record. CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C | Metric | Value | What it means | | ---------------------- | --------- | ----------------------------------------------------------------------------------------- | | Attack vector | Network | The vulnerable component can be reached over a network, possibly from the Internet. | | Attack complexity | High | The attack depends on conditions outside the attacker's control, so it takes preparation. | | Privileges required | Low | A basic user account is needed. | | User interaction | Required | A user has to do something first, such as opening a file or following a link. | | Scope | Unchanged | The impact stays within the vulnerable component. | | Confidentiality impact | High | Serious or total effect on the secrecy of data. | | Integrity impact | High | Serious or total effect on the trustworthiness of data. | | Availability impact | High | Serious or total effect on availability. | CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at [first.org/cvss](https://www.first.org/cvss/) . ### EPSS Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days. Score 0.11294 (11.3% probability) Percentile 96.0% Scores of Nov 10, 2026 Model v2026.06.15 ### CISA Known Exploited Vulnerabilities This CVE is listed in the CISA KEV catalog. Name in the catalog Microsoft Windows AppX Installer Spoofing Vulnerability Added to the catalog Dec 15, 2021 Federal due date Dec 29, 2021 Ransomware campaigns Known use ### CISA assessment as of Dec 14, 2021 Stakeholder-Specific Vulnerability Categorization (SSVC) decision points added by CISA. Exploitation Recorded by CISA as active Automatable no Technical impact total ## Affected products Products listed in the CVE record, as the CNA published them. - Microsoft App Installer - affected: 1.0.0.0 up to before publication ## References Links listed in the CVE record. They lead to other sites, which CubePath does not control. - [portal.msrc.microsoft.com/en-US/security-guidance/advisory/…](https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890) - [bleepingcomputer.com/news/microsoft/microsoft-disables-msix…](https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-msix-protocol-handler-abused-in-malware-attacks/) - [thehackernews.com/2023/12/microsoft-disables-msix-app-insta…](https://thehackernews.com/2023/12/microsoft-disables-msix-app-installer.html) - [microsoft.com/en-us/security/blog/2023/12/28/financially-mo…](https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/) - [github.com/ChrisTitusTech/winutil/pull/26](https://github.com/ChrisTitusTech/winutil/pull/26) ## Timeline 1. ID reserved Nov 16, 2021 2. Added to CISA KEV Dec 15, 2021 3. Record published Dec 15, 2021 4. Record last updated Aug 6, 2026 ## Look up another CVE ## About CubePath CubePath is a cloud provider with data centers in Europe and the United States. It offers VPS, bare metal servers and DDoS protection. [Cloud VPS](https://cubepath.com/vps) [DDoS protection](https://cubepath.com/ddos-protection) Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 20:02 UTC. [Sources and licenses](https://cubepath.com/security/cve/legal)