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Case File

CVE-2021-43890

HIGH · CVSS 7.1 EPSS 10.29% CISA KEV · Actively Exploited Public Exploit

Source: NVD + CISA KEV + EPSS (historical backfill) · Published 2021-12-15 · Last synced 2026-08-04

CyberRota Analysis

This is a high severity vulnerability with a CVSS score of 7.1. It affects Microsoft, Windows. It is listed in CISA's Known Exploited Vulnerabilities catalog, indicating confirmed active exploitation in the wild. Public exploit code or proof-of-concept references have been detected in its references. Its EPSS score suggests a 10.3% probability of exploitation in the next 30 days.

Public Exploit Signal

A public exploit, PoC, GitHub repository or Metasploit reference was detected for this CVE.

Detected Signals
exploit
GitHub PoC Links

Note: these links are listed for security research and verification purposes only.

CISA KEV Details

Status: This CVE is listed in CISA's Known Exploited Vulnerabilities catalog.

Ransomware use: Known

Added to KEV: 2021-12-15

Required action: Apply updates per vendor instructions.

CVE
CVE-2021-43890
Severity
HIGH
CVSS
7.1
EPSS
10.29%
Microsoft Windows

Original NVD 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.

Related CVEs

Other vulnerabilities affecting the same vendor(s)