# CVE-2020-13364: A backdoor in certain Zyxel products allows remote TELNET access via a CGI script.


- **Severity:** Medium 6.5 (`CVSS:3.0/AC:L/AV:N/A:N/C:L/I:L/PR:N/S:U/UI:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 6 Aug 2020
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-cwv4-27xg-6829

## What is CVE-2020-13364?

CVE-2020-13364 is a medium-severity vulnerability in n/a, published on 6 Aug 2020. 

### Official description

A backdoor in certain Zyxel products allows remote TELNET access via a CGI script. This affects NAS520 V5.21(AASZ.4)C0, V5.21(AASZ.0)C0, V5.11(AASZ.3)C0, and V5.11(AASZ.0)C0; NAS542 V5.11(ABAG.0)C0, V5.20(ABAG.1)C0, and V5.21(ABAG.3)C0; NSA325 v2_V4.81(AALS.0)C0 and V4.81(AAAJ.1)C0; NSA310 4.22(AFK.0)C0 and 4.22(AFK.1)C0; NAS326 V5.21(AAZF.8)C0, V5.11(AAZF.4)C0, V5.11(AAZF.2)C0, and V5.11(AAZF.3)C0; NSA310S V4.75(AALH.2)C0; NSA320S V4.75(AANV.2)C0 and V4.75(AANV.1)C0; NSA221 V4.41(AFM.1)C0; and NAS540 V5.21(AATB.5)C0 and V5.21(AATB.3)C0.

## Which versions are affected by CVE-2020-13364?

It affects 4 products.


Products: Zyxel Nas326 Firmware, Zyxel Nas520 Firmware, Zyxel Nas540 Firmware, Zyxel Nas542 Firmware.

## How do I fix CVE-2020-13364?

No fix has been published for CVE-2020-13364 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-13364 being exploited?

There is no known exploitation of CVE-2020-13364 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2023-27992](https://insights.sbomify.com/CVE-2023-27992/): Zyxel Multiple NAS Devices Command Injection (critical 9.8, exploited in the wild)
- [CVE-2024-6342](https://insights.sbomify.com/CVE-2024-6342/): Command injection in NAS326 firmware (critical 9.8)
- [CVE-2024-29972](https://insights.sbomify.com/CVE-2024-29972/): Command injection in NAS326 firmware (critical 9.8)
- [CVE-2024-29973](https://insights.sbomify.com/CVE-2024-29973/): Command injection in NAS326 firmware (critical 9.8)
- [CVE-2024-29974](https://insights.sbomify.com/CVE-2024-29974/): File upload in NAS326 firmware (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-13364 and fix it if it is affected.

What it is: CVE-2020-13364 is a medium-severity vulnerability in n/a, published on 6 Aug 2020. 
Exploitation: There is no known exploitation of CVE-2020-13364 in the wild and no public exploit code.

Affected product: n/a. 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-2020-13364/ (Markdown: https://insights.sbomify.com/CVE-2020-13364/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-13364
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-13364
- OSV: https://osv.dev/vulnerability/CVE-2020-13364

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-13364/
Summaries are generated and may contain mistakes; the official description above is the record.