---
id: "CVE-2021-1647"
kind: "vulnerability"
aliases: ["CVE-2021-1647"]
title: "Microsoft Defender: Microsoft Defender Remote Code Execution Vulnerability"
severity: "critical"
cvss: 7.8
epss: 0.39653
exploited: true
status: "open"
category: "other"
products: [{"name": "Microsoft Defender", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "microsoft-defender", "other", "windows"]
not_affected_if: ["defender-platform-already-updated", "non-windows-systems"]
published_at: "2021-01-12T20:15:30+00:00"
first_seen_at: "2026-10-23T19:11:53+00:00"
updated_at: "2026-10-23T21:57:35+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-1647", "first_seen_at": "2026-10-23T19:11:53+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2021-1647", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-1647", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Microsoft Defender: Microsoft Defender Remote Code Execution Vulnerability

Microsoft Defender (the antivirus engine) has a remote code execution flaw that CISA lists as actively exploited. An attacker who reaches the vulnerable component can run code on the machine.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Microsoft Defender affected ? fixed ?

## How to check

Check the Microsoft Defender Antimalware Platform version under Windows Security > Virus & threat protection > Protection updates, or run Get-MpComputerStatus in PowerShell and read AMProductVersion.

## Fix

Update Microsoft Defender Antimalware Platform to a version at or above the fixed build in Microsoft's advisory for CVE-2021-1647; the sources do not give the build number.
Normal Windows Update and Defender platform updates deliver the fix.

## Timeline

- 2026-10-23T19:11:53+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-1647
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2021-1647
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-1647

## From the sources

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

CISA required action: Apply updates per vendor instructions.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_