CVE-2021-43890Known exploitationNetwork attack vector

Malware installation via spoofed one-click packages

Published Dec 15, 2021 · Updated Aug 6, 2026

Spoofing in Microsoft App Installer allows remote attackers to install unintended software through a crafted package opened by a user. The ms-appinstaller URI handler launches one-click installation from a web link, allowing a malicious package to appear as an intended application without the normal download step. Exploitation requires phishing or social engineering and user interaction; installed code runs with the victim's rights, making administrative users more exposed.

CVSS severity7.1
High
EPSS probability10.29%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Spoofing in Microsoft App Installer allows remote attackers to install unintended software through a crafted package opened by a user. The ms-appinstaller URI handler launches one-click installation from a web link, allowing a malicious package to appear as an intended application without the normal download step. Exploitation requires phishing or social engineering and user interaction; installed code runs with the victim's rights, making administrative users more exposed.

The record

CVE
CVE-2021-43890
Published
Dec 15, 2021
Updated
Aug 6, 2026
Vendor
Microsoft
Product
App Installer
Classifications
T1204.002, T1566.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 6, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.0.0.0 <publication

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Microsoft · App Installerversion=1.0.0.0 <publication

Published CVSS scores

6.0NVDAV:N/AC:M/Au:S/C:P/I:P/A:P
7.1MicrosoftCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H
7.1NVDCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

T1204.002User Execution: Malicious File
T1566.001Phishing: Spearphishing Attachment

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo