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CVE-2021-43890 Microsoft CVE debrief

CVE-2021-43890 is a Microsoft Windows AppX Installer spoofing vulnerability that CISA added to its Known Exploited Vulnerabilities catalog on 2021-12-15. CISA marks it as known exploited and notes known ransomware campaign use, so Windows patching teams should treat remediation as urgent and follow vendor update guidance.

Vendor
Microsoft
Product
Windows
CVSS
Unknown
CISA KEV
Listed
Original CVE published
2021-12-15
Original CVE updated
2021-12-15
Advisory published
2021-12-15
Advisory updated
2021-12-15

Who should care

Windows administrators, endpoint and vulnerability management teams, SOC analysts, and any organization running Microsoft Windows systems should prioritize this CVE. It is especially important for teams responsible for rapid patch deployment and KEV-driven remediation.

Technical summary

The supplied source corpus identifies CVE-2021-43890 as a Microsoft Windows AppX Installer spoofing vulnerability. The CISA KEV record indicates it was added on 2021-12-15, marked as known exploited, and associated with known ransomware campaign use. The source item directs defenders to apply updates per vendor instructions.

Defensive priority

High urgency. Because this CVE is in CISA's Known Exploited Vulnerabilities catalog and is marked as used in known ransomware campaigns, remediation should be prioritized ahead of routine patch queues.

Recommended defensive actions

  • Inventory Microsoft Windows systems and identify any hosts that require the vendor update for CVE-2021-43890.
  • Apply Microsoft security updates per vendor instructions as soon as possible.
  • Track remediation against the CISA KEV due date of 2021-12-29 if your environment is still exposed.
  • Verify patch deployment and confirm the vulnerability is no longer present on managed Windows assets.
  • Use the official CVE and NVD references to validate internal tracking and ticketing.

Evidence notes

Evidence is limited to the supplied CISA KEV source item and official reference links. The KEV metadata states vendorProject Microsoft, product Windows, vulnerabilityName Microsoft Windows AppX Installer Spoofing Vulnerability, dateAdded 2021-12-15, dueDate 2021-12-29, knownRansomwareCampaignUse Known, and requiredAction Apply updates per vendor instructions. The source item also points to the NVD record for CVE-2021-43890. No additional technical mechanics are asserted beyond the supplied records.

Official resources

CISA added CVE-2021-43890 to the Known Exploited Vulnerabilities catalog on 2021-12-15 and flagged it as known exploited with known ransomware campaign use. Treat the CVE publication date as 2021-12-15.