# CVE-2021-31251: Auth bypass in n/a

> Attackers can bypass telnet authentication on CHIYU TCP/IP converters to gain privileged access and potentially execute code.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 4 Jun 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-fr6h-7w99-6jxc

## What is CVE-2021-31251?

CVE-2021-31251 is a critical authentication bypass vulnerability in n/a, published on 4 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An authentication bypass in telnet server in BF-430 and BF431 232/422 TCP/IP Converter, BF-450M and SEMAC from CHIYU Technology Inc allows obtaining a privileged connection with the target device by supplying a specially malformed request and an attacker may force the remote telnet server to believe that the user has already authenticated.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2021-31251?

It affects 10 products.


Products: Chiyu-Tech Bf-430 Firmware, Chiyu-Tech Bf-431 Firmware, Chiyu-Tech Bf-450m Firmware, Chiyu-Tech Semac D1 Firmware, Chiyu-Tech Semac D2 Firmware, Chiyu-Tech Semac D2 N300 Firmware, Chiyu-Tech Semac D4 Firmware, Chiyu-Tech Semac S1 Osdp Firmware, Chiyu-Tech Semac S2 Firmware, Chiyu-Tech Semac S3v3 Firmware.

## How do I fix CVE-2021-31251?

No fix has been published for CVE-2021-31251 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-31251 being exploited?

There is no known exploitation of CVE-2021-31251 in the wild and no public exploit code.

Public exploit code:

- CHIYU IoT Devices - 'Telnet' Authentication Bypass (exploitdb)

## Other vulnerabilities in n/a

- [CVE-2021-31249](https://insights.sbomify.com/CVE-2021-31249/): Other in n/a (medium 6.5)
- [CVE-2021-31252](https://insights.sbomify.com/CVE-2021-31252/): Open redirect in n/a (medium 6.1)
- [CVE-2021-31641](https://insights.sbomify.com/CVE-2021-31641/): Cross-site scripting in n/a (medium 6.1)
- [CVE-2021-31250](https://insights.sbomify.com/CVE-2021-31250/): Cross-site scripting in n/a (medium 5.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-31251 and fix it if it is affected.

What it is: CVE-2021-31251 is a critical authentication bypass vulnerability in n/a, published on 4 Jun 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-2021-31251 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-2021-31251/ (Markdown: https://insights.sbomify.com/CVE-2021-31251/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-31251
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-31251
- OSV: https://osv.dev/vulnerability/CVE-2021-31251

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-31251/
Summaries are generated and may contain mistakes; the official description above is the record.