CVE-2021-43890: in the CISA KEV catalogue
Microsoft Windows AppX Installer Spoofing Vulnerability. CISA added CVE-2021-43890 to the Known Exploited Vulnerabilities catalogue on 2021-12-15 with a default due date of 2021-12-29. Known ransomware campaign use: Known. Forensic triage flag: No.
Microsoft Windows AppX Installer contains a spoofing vulnerability which has a high impacts to confidentiality, integrity, and availability. (CISA description)
- Vendor / product
- Microsoft Windows
- CWE
- Not listed
- CISA required action
- Apply updates per vendor instructions.
- EPSS
- 11%, percentile 95 (scored 2026-11-03)
EPSS puts about 11 in 100 odds (11%) on exploitation activity being observed in the next 30 days. Its score is higher than or equal to that of 95% of scored CVEs. This is a model estimate about exploitation anywhere, not about your environment.
Vendor and reference links (from CISA)
Your own deadline under CISA BOD 26-04 depends on exposure, automatability and technical impact: work it out with the BOD 26-04 calculator.
Frequently asked questions
Is CVE-2021-43890 in the CISA KEV catalogue?
Yes. CISA added CVE-2021-43890 (Microsoft Windows AppX Installer Spoofing Vulnerability) to the Known Exploited Vulnerabilities catalogue on 2021-12-15. CISA's default due date for it is 2021-12-29.
Is CVE-2021-43890 used in ransomware attacks?
CISA marks known ransomware campaign use as Known for CVE-2021-43890.
What should I do about CVE-2021-43890?
CISA's required action: Apply updates per vendor instructions.
Sources
- CISA, Known Exploited Vulnerabilities Catalog (accessed 2026-11-03)
- FIRST, Exploit Prediction Scoring System (EPSS) (EPSS by FIRST; scores generated by Empirical Security)
- NVD record for CVE-2021-43890