Exploited vulnerability · CISA KEV

Is CVE-2021-1647 exploited? Yes: in CISA KEV since 3 Nov 2021

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

Yes. CVE-2021-1647, Microsoft Defender Remote Code Execution Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 3 Nov 2021, 295 days after it was published. It affects Microsoft Defender. If you run it, CISA's required action is: Apply updates per vendor instructions.

What it is

Microsoft Defender contains an unspecified vulnerability that allows for remote code execution.

What to do

1. Check whether you run it. Look for Defender 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 12 Jan 2021.
4. Get told next time. Email alerts when CISA adds a CVE for Microsoft.

Other exploited CVEs in Defender

• CVE-2026-41091: Microsoft Defender Link Following Vulnerability (20 May 2026)
• CVE-2026-45498: Microsoft Defender Denial of Service Vulnerability (20 May 2026)
• CVE-2026-33825: Microsoft Defender Insufficient Granularity of Access Control Vulnerability (22 Apr 2026)
• CVE-2022-44698: Microsoft Defender SmartScreen Security Feature Bypass Vulnerability (13 Dec 2022)

References

• nvd.nist.gov/vuln/detail/CVE-2021-1647

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 November 2021 · Microsoft scorecard · act-now radar.