# CVE-2021-43890: Microsoft Windows AppX Installer Spoofing Vulnerability

Source: https://junglewise.ai/threats/cve-2021-43890-microsoft-windows-appx-installer-spoofing-vulnerability  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2021-12-15. Updated: 2026-05-10  
License: CC BY 4.0 with a link back

CVE-2021-43890 · Severity: critical · CVSS 7.1 · Exploited in the wild · Published 2021-12-15

Microsoft Windows AppX Installer contains a spoofing vulnerability that allows attackers to craft malicious attachments for phishing campaigns. Exploitation involves convincing a user to open a specially crafted package, which has been observed in the wild delivering malware families such as Emotet, Trickbot, and Bazaloader.

Technologies: [Microsoft Windows](https://junglewise.ai/threats/technologies/windows). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2021-43890 exploited in the wild?** Yes. CVE-2021-43890 is known to be exploited in the wild, first recorded on 15 December 2021. Treat it as urgent.

**How severe is CVE-2021-43890?** Critical severity, with a CVSS score of 7.1, published 15 December 2021.

**Which products and versions are affected?** Microsoft Windows AppX Installer.

**Is there a fix for CVE-2021-43890?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2021-43890 attacked?** It is attacked over the network, in an operating system.

**Am I affected by CVE-2021-43890?** Check whether you run Microsoft Windows. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Affected products

- Microsoft Windows AppX Installer

## Timeline

- 2021-12-15: disclosed
- 2021-12-15: kev added: Added to CISA Known Exploited Vulnerabilities Catalog
- 2021-12-15: advisory
- 2023-12-27: other: Microsoft updated App Installer to disable the ms-appinstaller protocol by default due to increased abuse.

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