# CVE-2021-27239: Memory corruption in Multiple Routers

> Network-adjacent attackers can execute arbitrary code as root on NETGEAR routers via a stack buffer overflow in the upnpd service.

- **Severity:** High 8.8 (`CVSS:3.0/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 29 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-hqww-3wrx-q5gv

## What is CVE-2021-27239?

CVE-2021-27239 is a high-severity memory corruption vulnerability in Netgear D6220 Firmware, published on 29 Mar 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of NETGEAR R6400 and R6700 firmware version 1.0.4.98 routers. Authentication is not required to exploit this vulnerability. The specific flaw exists within the upnpd service, which listens on UDP port 1900 by default. A crafted MX header field in an SSDP message can trigger an overflow of a fixed-length stack-based buffer. An attacker can leverage this vulnerability to execute code in the context of root. Was ZDI-CAN-11851.

Weakness: CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2021-27239?

It affects 35 products.


Products: Netgear D6220 Firmware, Netgear D6400 Firmware, Netgear D7000 Firmware, Netgear D8500 Firmware, Netgear Dc112a Firmware, Netgear Ex7000 Firmware, Netgear Ex7500 Firmware, Netgear R6250 Firmware, Netgear R6300 Firmware, Netgear R6400 Firmware, Netgear R6700 Firmware, Netgear R6900p Firmware, Netgear R7000 Firmware, Netgear R7000p Firmware, Netgear R7100lg Firmware, Netgear R7850 Firmware, Netgear R7900 Firmware, Netgear R7900p Firmware, Netgear R7960p Firmware, Netgear R8000 Firmware and 15 more.

## How do I fix CVE-2021-27239?

No fix has been published for CVE-2021-27239 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-27239 being exploited?

There is no known exploitation of CVE-2021-27239 in the wild and no public exploit code.

## Other vulnerabilities in Netgear D6220 Firmware

- [CVE-2016-6277](https://insights.sbomify.com/CVE-2016-6277/): NETGEAR Multiple Routers Remote Code Execution (high 8.8, exploited in the wild)
- [CVE-2021-45527](https://insights.sbomify.com/CVE-2021-45527/): Memory corruption in n/a (critical 9.6)
- [CVE-2021-45610](https://insights.sbomify.com/CVE-2021-45610/): Memory corruption in n/a (critical 9.6)
- [CVE-2021-45638](https://insights.sbomify.com/CVE-2021-45638/): Memory corruption in n/a (critical 9.6)
- [CVE-2021-34982](https://insights.sbomify.com/CVE-2021-34982/): NETGEAR Multiple Routers httpd Stack-based Buffer Overflow Remote Code Execution Vulnerability (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-27239 and fix it if it is affected.

What it is: CVE-2021-27239 is a high-severity memory corruption vulnerability in Netgear D6220 Firmware, published on 29 Mar 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-27239 in the wild and no public exploit code.

Affected product: Netgear D6220 Firmware. 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-2021-27239/ (Markdown: https://insights.sbomify.com/CVE-2021-27239/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-27239
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-27239
- OSV: https://osv.dev/vulnerability/CVE-2021-27239

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-27239/
Summaries are generated and may contain mistakes; the official description above is the record.