CVE-2021-43890

high

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.

From the Tenable Blog

Microsoft’s December 2021 Patch Tuesday Addresses 67 CVEs (CVE-2021-43890)
Microsoft’s December 2021 Patch Tuesday Addresses 67 CVEs (CVE-2021-43890)

Published: 2021-12-14

Microsoft addresses 67 CVEs in its December 2021 Patch Tuesday release, including a zero-day vulnerability that has been exploited in the wild.

References

https://www.securityweek.com/microsoft-confirms-windows-exploits-bypassing-security-features/

https://www.tenable.com/blog/analyzing-the-vulnerabilities-associated-with-the-top-malware-strains-of-2021

https://www.tenable.com/blog/microsofts-december-2021-patch-tuesday-addresses-67-cves-cve-2021-43890

https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/

https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-msix-protocol-handler-abused-in-malware-attacks/

https://thehackernews.com/2023/12/microsoft-disables-msix-app-installer.html

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890

https://github.com/ChrisTitusTech/winutil/pull/26

Details

Source: Mitre, NVD

Published: 2021-12-15

Updated: 2024-11-21

Risk Information

CVSS v2

Base Score: 6

Vector: CVSS2#AV:N/AC:M/Au:S/C:P/I:P/A:P

Severity: Medium

CVSS v3

Base Score: 7.1

Vector: CVSS:3.0/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H

Severity: High