CVE-2021-43890
What it is
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.
At a glance
- Exploitability
- Can be exploited over the network with a low-privilege account, but needs a user to act. High risk of data exposure, data tampering, service disruption.
- In the wild
- CISA lists this as exploited in real attacks. Treat as urgent.
- Fix
- A patch, advisory or fixed version is referenced. Upgrade or apply it.
Timeline
- ReservedThe CVE id was reserved by its CNA
- 2021-12-15 Exploited in the wildAdded to CISA's Known Exploited Vulnerabilities list
- PublishedDisclosed publicly on CVE.org and NVD
- 2021-12-29 Remediation deadlineCISA's due date for federal agencies to fix it
- Last updatedMost recent change to the record
Why it ranks here
- Exploited in the wild: yes, CISA lists it. This puts it above everything that is not.
- Exploit odds: 11.3% in the next 30 days (EPSS).
- Severity: 7.1 HIGH (CVSS).
- Fix: a patch or advisory is linked.
Details
- Published
- Last modified
- Added to CISA KEV
- 2021-12-15
- Exploit probability
- 11.3% · EPSS, next 30 days
- Record status
- Analyzed
Affected
- Microsoft App Installer < 1.16
- Microsoft App Installer < 1.11
Attack profile CVSS 3.1 · 7.1
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- Low
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Raw vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H
Is it in your code?
Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.
Read https://cve-list.com/agent/cve/CVE-2021-43890.md and follow it. Check whether this project is affected by CVE-2021-43890. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.
Fix and advisories
- https://github.com/ChrisTitusTech/winutil/pull/26
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890
- https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/
- https://github.com/ChrisTitusTech/winutil/pull/26
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890
- https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/
References
- https://github.com/ChrisTitusTech/winutil/pull/26
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890
- https://thehackernews.com/2023/12/microsoft-disables-msix-app-installer.html
- https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-msix-protocol-handler-abused-in-malware-attacks/
- https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/
- https://github.com/ChrisTitusTech/winutil/pull/26
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43890
- https://thehackernews.com/2023/12/microsoft-disables-msix-app-installer.html
- https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-msix-protocol-handler-abused-in-malware-attacks/
- https://www.microsoft.com/en-us/security/blog/2023/12/28/financially-motivated-threat-actors-misusing-app-installer/
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-43890