# CVE-2021-31166: Microsoft HTTP Protocol Stack Remote Code Execution

> Remote attackers can execute arbitrary code via the Windows HTTP Protocol Stack, requiring immediate patching for Windows 10 and Server.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C`)
- **Exploited in the wild:** Yes, since 6 Apr 2022 (CISA KEV)
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 11 May 2021
- **Updated:** 21 Oct 2025
- **Also known as:** GHSA-3mj9-c62w-jw5w

## What is CVE-2021-31166?

CVE-2021-31166 is a critical use after free vulnerability in Microsoft Windows 10 20h2, published on 11 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

HTTP Protocol Stack Remote Code Execution Vulnerability

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-31166?

It affects 4 products.


Products: Microsoft Windows 10 2004, Microsoft Windows 10 20h2, Microsoft Windows Server 2004, Microsoft Windows Server 20h2.

## How do I fix CVE-2021-31166?

No fix has been published for CVE-2021-31166 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 27 Apr 2022.

## Is CVE-2021-31166 being exploited?

Yes. Attackers have exploited CVE-2021-31166 in the wild since at least 6 Apr 2022.

Public exploit code:

- Proof of concept for CVE-2021-31166, a remote HTTP.sys use-after-free triggered remotely. (github_poc): https://github.com/0vercl0k/CVE-2021-31166
- Windows HTTP协议栈远程代码执行漏洞 CVE-2021-31166 (github_poc): https://github.com/ZZ-SOCMAP/CVE-2021-31166
- HTTP Protocol Stack CVE-2021-31166 (github_poc): https://github.com/corelight/CVE-2021-31166
- PoC for CVE-2021-31166, a remote HTTP.sys use-after-free triggered remotely. Although it was defined as remote command execution, it can only cause the system to crash. (github_poc): https://github.com/zha0gongz1/CVE-2021-31166
- PoC for CVE-2021-31166 and CVE-2022-21907 (github_poc): https://github.com/0xmaximus/Home-Demolisher
- Exploit for MS Http Protocol Stack RCE vulnerability (CVE-2021-31166) (github_poc): https://github.com/y0g3sh-99/CVE-2021-31166-Exploit

## Other vulnerabilities in Microsoft Windows 10 20h2

- [CVE-2021-41357](https://insights.sbomify.com/CVE-2021-41357/): Microsoft Win32k Privilege Escalation (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-31166 and fix it if it is affected.

What it is: CVE-2021-31166 is a critical use after free vulnerability in Microsoft Windows 10 20h2, published on 11 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2021-31166 in the wild since at least 6 Apr 2022.

Affected product: Microsoft Windows 10 20h2. 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-2021-31166/ (Markdown: https://insights.sbomify.com/CVE-2021-31166/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-31166
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-31166
- OSV: https://osv.dev/vulnerability/CVE-2021-31166

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-31166/
Summaries are generated and may contain mistakes; the official description above is the record.