# CVE-2021-4029: Command injection in ARMOR Z1 (NBG6816) firmware

> Attackers can execute arbitrary OS commands on Zyxel ARMOR Z1/Z2 routers via the LAN interface due to a command injection flaw in the CGI program.

- **Severity:** High 8.8 (`CVSS:3.1/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:** 22 Feb 2022
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-47g9-xhm7-62xr

## What is CVE-2021-4029?

CVE-2021-4029 is a high-severity command injection vulnerability in Zyxel ARMOR Z1 (NBG6816) firmware, published on 22 Feb 2022. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A command injection vulnerability in the CGI program of the Zyxel ARMOR Z1/Z2 firmware could allow an attacker to execute arbitrary OS commands via a LAN interface.

Weakness: CWE-78 (Improper Neutralization of Special Elements used in an OS Command)

## Which versions are affected by CVE-2021-4029?

It affects 2 products.


Products: Zyxel Nbg6816 Firmware, Zyxel Nbg6817 Firmware.

## How do I fix CVE-2021-4029?

No fix has been published for CVE-2021-4029 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-4029 being exploited?

There is no known exploitation of CVE-2021-4029 in the wild and no public exploit code.

## Other vulnerabilities in Zyxel ARMOR Z1 (NBG6816) firmware

- [CVE-2021-4030](https://insights.sbomify.com/CVE-2021-4030/): Cross-site request forgery in ARMOR Z1 (NBG6816) firmware (high 8.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-4029 and fix it if it is affected.

What it is: CVE-2021-4029 is a high-severity command injection vulnerability in Zyxel ARMOR Z1 (NBG6816) firmware, published on 22 Feb 2022. 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-2021-4029 in the wild and no public exploit code.

Affected product: Zyxel ARMOR Z1 (NBG6816) 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-2021-4029/ (Markdown: https://insights.sbomify.com/CVE-2021-4029/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-4029
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-4029
- OSV: https://osv.dev/vulnerability/CVE-2021-4029

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-4029/
Summaries are generated and may contain mistakes; the official description above is the record.