# CVE-2021-1647: Microsoft Defender Remote Code Execution

> An attacker can execute arbitrary code on systems running Microsoft Defender or related endpoint protection products.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:P/RL:O/RC:C`)
- **Exploited in the wild:** Yes, since 3 Nov 2021 (CISA KEV)
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Jan 2021
- **Updated:** 21 Oct 2025
- **Also known as:** GHSA-4v4q-r2mh-q7w6

## What is CVE-2021-1647?

CVE-2021-1647 is a high-severity code injection vulnerability in Microsoft Security Essentials, published on 12 Jan 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Microsoft Defender Remote Code Execution Vulnerability

## Which versions are affected by CVE-2021-1647?

It affects 3 products.


Products: Microsoft Security Essentials, Microsoft System Center Endpoint Protection, Microsoft Windows Defender.

## How do I fix CVE-2021-1647?

No fix has been published for CVE-2021-1647 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 17 Nov 2021.

## Is CVE-2021-1647 being exploited?

Yes. Attackers have exploited CVE-2021-1647 in the wild since at least 3 Nov 2021.

Public exploit code:

- https://github.com/findcool/cve-2021-1647 (github_poc): https://github.com/findcool/cve-2021-1647

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-1647 and fix it if it is affected.

What it is: CVE-2021-1647 is a high-severity code injection vulnerability in Microsoft Security Essentials, published on 12 Jan 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2021-1647 in the wild since at least 3 Nov 2021.

Affected product: Microsoft Security Essentials. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-1647/ (Markdown: https://insights.sbomify.com/CVE-2021-1647/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-1647
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-1647
- OSV: https://osv.dev/vulnerability/CVE-2021-1647

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-1647/
Summaries are generated and may contain mistakes; the official description above is the record.