Exploited vulnerability · CISA KEV

Is CVE-2021-43890 exploited? Yes: in CISA KEV since 15 Dec 2021

Gociux · Microsoft Windows · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2021-43890, Microsoft Windows AppX Installer Spoofing Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 15 Dec 2021, the day it was published. It is known to be used in ransomware campaigns. It affects Microsoft Windows. If you run it, CISA's required action is: Apply updates per vendor instructions.

What it is

Microsoft Windows AppX Installer contains a spoofing vulnerability which has a high impacts to confidentiality, integrity, and availability.

What to do

1. Check whether you run it. Look for Windows in your asset inventory, including appliances and cloud images. Stack check lists every exploited Microsoft CVE at once.
2. Apply the fix. Apply updates per vendor instructions.
3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 15 Dec 2021.
4. Get told next time. Email alerts when CISA adds a CVE for Microsoft.

Other exploited CVEs in Windows

• CVE-2026-96951: Microsoft Windows Command Injection Vulnerability (13 Oct 2026)
• CVE-2026-81963: Microsoft Windows Link Following Vulnerability (8 Sep 2026)
• CVE-2026-85880: Microsoft Windows Heap-Based Buffer Overflow Vulnerability (8 Sep 2026)
• CVE-2008-4250: Microsoft Windows Buffer Overflow Vulnerability (20 May 2026)
• CVE-2026-32202: Microsoft Windows Protection Mechanism Failure Vulnerability (28 Apr 2026)
• CVE-2025-60710: Microsoft Windows Link Following Vulnerability (13 Apr 2026)

References

• nvd.nist.gov/vuln/detail/CVE-2021-43890

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in December 2021 · Microsoft scorecard · act-now radar.