Vulnerability Details : CVE-2021-43890
Potential exploit
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.
Products affected by CVE-2021-43890
- cpe:2.3:a:microsoft:app_installer:*:*:*:*:*:*:*:*
- cpe:2.3:a:microsoft:app_installer:*:*:*:*:*:*:*:*
CVE-2021-43890 is in the CISA Known Exploited Vulnerabilities Catalog
CISA vulnerability name:
Microsoft Windows AppX Installer Spoofing Vulnerability
CISA required action:
Apply updates per vendor instructions.
CISA description:
Microsoft Windows AppX Installer contains a spoofing vulnerability which has a high impacts to confidentiality, integrity, and availability.
Notes:
https://nvd.nist.gov/vuln/detail/CVE-2021-43890
Added on
2021-12-15
Action due date
2021-12-29
Exploit prediction scoring system (EPSS) score for CVE-2021-43890
27.25%
Probability of exploitation activity in the next 30 days
EPSS Score History
~ 97 %
Percentile, the proportion of vulnerabilities that are scored at or less
CVSS scores for CVE-2021-43890
Base Score | Base Severity | CVSS Vector | Exploitability Score | Impact Score | Score Source | First Seen |
---|---|---|---|---|---|---|
6.0
|
MEDIUM | AV:N/AC:M/Au:S/C:P/I:P/A:P |
6.8
|
6.4
|
NIST | |
7.1
|
HIGH | CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H |
1.2
|
5.9
|
NIST | |
7.1
|
HIGH | CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H |
1.2
|
5.9
|
Microsoft Corporation |
References for CVE-2021-43890
-
https://thehackernews.com/2023/12/microsoft-disables-msix-app-installer.html
Microsoft Disables MSIX App Installer Protocol Widely Used in Malware AttacksPress/Media Coverage;Third Party Advisory
-
https://github.com/ChrisTitusTech/winutil/pull/26
Added Winget Check and Install by mrhaydendp · Pull Request #26 · ChrisTitusTech/winutil · GitHubIssue Tracking
-
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890
CVE-2021-43890 - Security Update Guide - Microsoft - Windows AppX Installer Spoofing VulnerabilityPatch;Vendor Advisory
-
https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-msix-protocol-handler-abused-in-malware-attacks/
Microsoft disables MSIX protocol handler abused in malware attacksPress/Media Coverage;Third Party Advisory
-
https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/
Financially motivated threat actors misusing App Installer | Microsoft Security BlogExploit;Vendor Advisory
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