# CVE-2021-35034: Security feature bypass in NBG6604 series firmware

> Remote attackers can bypass session expiration to access Zyxel NBG6604 devices if they intercept the correct token.

- **Severity:** High 7.4 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 29 Dec 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-38gc-w4h9-7pmf

## What is CVE-2021-35034?

CVE-2021-35034 is a high-severity vulnerability in Zyxel NBG6604 series firmware, published on 29 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An insufficient session expiration vulnerability in the CGI program of the Zyxel NBG6604 firmware could allow a remote attacker to access the device if the correct token can be intercepted.

Weakness: CWE-613 (DEPRECATED: Insufficient Session Expiration)

## Which versions are affected by CVE-2021-35034?

It affects 1 product.


Products: Zyxel Nbg6604 Firmware.

## How do I fix CVE-2021-35034?

No fix has been published for CVE-2021-35034 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-35034 being exploited?

There is no known exploitation of CVE-2021-35034 in the wild and no public exploit code.

## Other vulnerabilities in Zyxel NBG6604 series firmware

- [CVE-2023-33013](https://insights.sbomify.com/CVE-2023-33013/): Command injection in NBG6604 firmware (high 8.8)
- [CVE-2023-22919](https://insights.sbomify.com/CVE-2023-22919/): Command injection in NBG6604 firmware (high 8.8)
- [CVE-2021-35035](https://insights.sbomify.com/CVE-2021-35035/): Information disclosure in NBG6604 series firmware (medium 4.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-35034 and fix it if it is affected.

What it is: CVE-2021-35034 is a high-severity vulnerability in Zyxel NBG6604 series firmware, published on 29 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-35034 in the wild and no public exploit code.

Affected product: Zyxel NBG6604 series 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-2021-35034/ (Markdown: https://insights.sbomify.com/CVE-2021-35034/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-35034
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-35034
- OSV: https://osv.dev/vulnerability/CVE-2021-35034

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-35034/
Summaries are generated and may contain mistakes; the official description above is the record.