# CVE-2017-20204: DBLTek GoIP Telnet Admin Interface Undocumented Backdoor

> Remote attackers can bypass authentication on DBLTek GoIP devices via a flawed Telnet backdoor to gain root access and execute arbitrary code.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Oct 2025
- **Updated:** 15 Oct 2025
- **Also known as:** GHSA-5g7c-29rx-62p8

## What is CVE-2017-20204?

CVE-2017-20204 is a critical authentication bypass vulnerability in DBL Technology (DBLTek) GoIP, published on 15 Oct 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

DBLTek GoIP devices (models GoIP 1, 4, 8, 16, and 32) contain an undocumented vendor backdoor in the Telnet administrative interface that allows remote authentication as an undocumented user via a proprietary challenge–response scheme which is fundamentally flawed. Because the challenge response can be computed from the challenge itself, a remote attacker can authenticate without knowledge of a secret and obtain a root shell on the device. This can lead to persistent remote code execution, full device compromise, and arbitrary control of the device and any managed services. The firmware used within these devices was updated in December 2016 to make this vulnerability more complex to exploit. However, it is unknown if DBLTek has taken steps to fully mitigate.

Weakness: CWE-1242 (Inclusion of Undocumented Features or Chicken Bits)

## Which versions are affected by CVE-2017-20204?


## How do I fix CVE-2017-20204?

No fix has been published for CVE-2017-20204 yet. Limit exposure of the affected software until one is available.

## Is CVE-2017-20204 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2017-20204 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2017-20204 and fix it if it is affected.

What it is: CVE-2017-20204 is a critical authentication bypass vulnerability in DBL Technology (DBLTek) GoIP, published on 15 Oct 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2017-20204 exists.

Affected product: DBL Technology (DBLTek) GoIP. 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-2017-20204/ (Markdown: https://insights.sbomify.com/CVE-2017-20204/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2017-20204
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2017-20204
- OSV: https://osv.dev/vulnerability/CVE-2017-20204

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From sbomify Insights: https://insights.sbomify.com/CVE-2017-20204/
Summaries are generated and may contain mistakes; the official description above is the record.