# CVE-2021-35030: Cross-site scripting in GS1900-8 Firmware

> An authenticated local user can execute cross-site scripting attacks via crafted LLDP packets in Zyxel GS1900-8 firmware.

- **Severity:** Low 3.5 (`CVSS:3.1/AV:A/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 26 Jul 2021
- **Updated:** 17 Sep 2024
- **Also known as:** GHSA-g78g-pgq7-f6cr

## What is CVE-2021-35030?

CVE-2021-35030 is a low-severity cross-site scripting vulnerability in Zyxel GS1900-8 Firmware, published on 26 Jul 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A vulnerability was found in the CGI program in Zyxel GS1900-8 firmware version V2.60, that did not properly sterilize packet contents and could allow an authenticated, local user to perform a cross-site scripting (XSS) attack via a crafted LLDP packet.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2021-35030?

It affects 12 products.


Products: Zyxel Gs1900-10hp Firmware, Zyxel Gs1900-16 Firmware, Zyxel Gs1900-24 Firmware, Zyxel Gs1900-24e Firmware, Zyxel Gs1900-24ep Firmware, Zyxel Gs1900-24hp Firmware, Zyxel Gs1900-24hpv2 Firmware, Zyxel Gs1900-48 Firmware, Zyxel Gs1900-48hp Firmware, Zyxel Gs1900-48hpv2 Firmware, Zyxel Gs1900-8 Firmware, Zyxel Gs1900-8hp Firmware.

## How do I fix CVE-2021-35030?

No fix has been published for CVE-2021-35030 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-35030 being exploited?

There is no known exploitation of CVE-2021-35030 in the wild and no public exploit code.

## Other vulnerabilities in Zyxel GS1900-8 Firmware

- [CVE-2026-7273](https://insights.sbomify.com/CVE-2026-7273/): Zyxel GS1900 Series Switches Stack-Based Buffer Overflow (high 8.8, exploited in the wild)
- [CVE-2019-15800](https://insights.sbomify.com/CVE-2019-15800/): Command injection in n/a (critical 9.8)
- [CVE-2015-5988](https://insights.sbomify.com/CVE-2015-5988/): Hardcoded credentials in n/a (critical 9.8)
- [CVE-2015-5989](https://insights.sbomify.com/CVE-2015-5989/): Auth bypass in n/a (critical 9.8)
- [CVE-2019-15803](https://insights.sbomify.com/CVE-2019-15803/): Auth bypass in n/a (critical 9.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-35030 and fix it if it is affected.

What it is: CVE-2021-35030 is a low-severity cross-site scripting vulnerability in Zyxel GS1900-8 Firmware, published on 26 Jul 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-2021-35030 in the wild and no public exploit code.

Affected product: Zyxel GS1900-8 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-2021-35030/ (Markdown: https://insights.sbomify.com/CVE-2021-35030/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-35030
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-35030
- OSV: https://osv.dev/vulnerability/CVE-2021-35030

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-35030/
Summaries are generated and may contain mistakes; the official description above is the record.