CVEs / CVE-2021-43890
CVE-2021-43890: Microsoft Windows AppX Installer Spoofing Vulnerability
- Known exploited in the CISA KEV catalog since 15 Dec 2021
- high 7.1 CVSS 3.1 (NVD)
- EPSS 11.2% chance of exploitation in the next 30 days, higher than 95% of CVEs (30 Oct 2026)
- Last changed at its sources
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Summary
Microsoft Windows AppX Installer contains a spoofing vulnerability which has a high impacts to confidentiality, integrity, and availability.
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.
Affected and fixed versions
| Product | Affected | Fixed in |
|---|---|---|
| Microsoft App Installer | from 1.0.0.0, before publication | publication |
Exploitation
| In CISA KEV since | 15 Dec 2021 |
|---|---|
| Due date for US federal agencies | 29 Dec 2021 |
| Used in ransomware campaigns | Known |
| Required action | Apply updates per vendor instructions. |
Severity
| CVSS 3.1 | 7.1 highCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:HScored by NVD |
|---|
References
- CVE-2021-43890 on NVD
- CVE-2021-43890 in the CISA KEV catalog
- https://github.com/ChrisTitusTech/winutil/pull/26 Issue Tracking
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890 Patch, Vendor Advisory
- https://thehackernews.com/2023/12/microsoft-disables-msix-app-installer.html Press/Media Coverage, Third Party Advisory
- https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-msix-protocol-handler-abused-in-malware-attacks/ Press/Media Coverage, Third Party Advisory
- https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/ Exploit, Vendor Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-43890 US Government Resource
Sources
Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.
This product uses data from the NVD API but is not endorsed or certified by the NVD.