CVE-2021-1647 Microsoft Defender Remote Code Execution Vulnerability
Microsoft Defender contains an unspecified vulnerability that allows for remote code execution.
From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.
Should You Worry?
- CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 3 Nov 2021.
- Rated High severity (CVSS 7.8, scored by Vendor).
- It has been in the catalogue for 1,829 days. Systems still unpatched now have almost certainly been scanned for it.
What It Is
Microsoft Defender Remote Code Execution Vulnerability
Affected Versions
| Product | Versions |
|---|---|
| Microsoft Microsoft System Center Endpoint Protection | N/A |
| Microsoft Microsoft System Center 2012 R2 Endpoint Protection | N/A |
| Microsoft Microsoft Security Essentials | N/A |
| Microsoft Microsoft System Center 2012 Endpoint Protection | N/A |
| Microsoft Windows Defender | N/A |
From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.
What To Do Now
- 1
Find it
Search your asset inventory and external attack surface for Microsoft Defender. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management - 2
- 3
Hunt for compromise
If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.
Incident Response - 4
Prove it is fixed
Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.
Penetration Testing
Vendor Advisories
The Compliance Clock
General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.
Not Sure If You Are Exposed?
Our attack surface and vulnerability teams can check your internet-facing estate for CVE-2021-1647 and every other exploited flaw on the list.