# CVE-2021-27173: Auth bypass in n/a

> An unauthenticated backdoor API on FiberHome routers disables the firewall and enables Telnet, allowing attackers to gain remote command-line access.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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:** 10 Feb 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-vr73-2fhc-cc9m

## What is CVE-2021-27173?

CVE-2021-27173 is a high-severity authentication bypass vulnerability in n/a, published on 10 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An issue was discovered on FiberHome HG6245D devices through RP2613. There is a telnet?enable=0&key=calculated(BR0_MAC) backdoor API, without authentication, provided by the HTTP server. This will remove firewall rules and allow an attacker to reach the telnet server (used for the CLI).

## Which versions are affected by CVE-2021-27173?

It affects 1 product.


Products: Fiberhome Hg6245d Firmware.

## How do I fix CVE-2021-27173?

No fix has been published for CVE-2021-27173 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-27173 being exploited?

There is no known exploitation of CVE-2021-27173 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2021-27141](https://insights.sbomify.com/CVE-2021-27141/): Hardcoded credentials in n/a (critical 9.8)
- [CVE-2021-27143](https://insights.sbomify.com/CVE-2021-27143/): Hardcoded credentials in n/a (critical 9.8)
- [CVE-2021-27144](https://insights.sbomify.com/CVE-2021-27144/): Hardcoded credentials in n/a (critical 9.8)
- [CVE-2021-27145](https://insights.sbomify.com/CVE-2021-27145/): Hardcoded credentials in n/a (critical 9.8)
- [CVE-2021-27146](https://insights.sbomify.com/CVE-2021-27146/): Hardcoded credentials in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-27173 and fix it if it is affected.

What it is: CVE-2021-27173 is a high-severity authentication bypass vulnerability in n/a, published on 10 Feb 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-2021-27173 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-2021-27173/ (Markdown: https://insights.sbomify.com/CVE-2021-27173/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-27173
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-27173
- OSV: https://osv.dev/vulnerability/CVE-2021-27173

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-27173/
Summaries are generated and may contain mistakes; the official description above is the record.