# CVE-2025-3666: TOTOLINK A3700R cstecgi.cgi setDdnsCfg access control

> Remote attackers can bypass access controls to modify DDNS settings on TOTOLINK A3700R routers due to improper authorization checks.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/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:** 16 Apr 2025
- **Updated:** 16 Apr 2025
- **Also known as:** GHSA-pvmj-4jf2-h6jf

## What is CVE-2025-3666?

CVE-2025-3666 is a medium-severity missing authorization vulnerability in TOTOLINK A3700R, published on 16 Apr 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability was found in TOTOLINK A3700R 9.1.2u.5822_B20200513 and classified as critical. Affected by this issue is the function setDdnsCfg of the file /cgi-bin/cstecgi.cgi. The manipulation leads to improper access controls. The attack may be launched remotely. The exploit has been disclosed to the public and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

Weakness: CWE-284 (Improper Access Control), CWE-266 (Incorrect Privilege Assignment)

## Which versions are affected by CVE-2025-3666?

It affects 1 product.


Products: Totolink A3700r Firmware.

## How do I fix CVE-2025-3666?

No fix has been published for CVE-2025-3666 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-3666 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-3666 exists.

## Other vulnerabilities in TOTOLINK A3700R

- [CVE-2024-42545](https://insights.sbomify.com/CVE-2024-42545/): Memory corruption in n/a (critical 9.8)
- [CVE-2024-37637](https://insights.sbomify.com/CVE-2024-37637/): Memory corruption in n/a (critical 9.8)
- [CVE-2024-37634](https://insights.sbomify.com/CVE-2024-37634/): Memory corruption in n/a (critical 9.8)
- [CVE-2024-37635](https://insights.sbomify.com/CVE-2024-37635/): Memory corruption in n/a (critical 9.8)
- [CVE-2024-22660](https://insights.sbomify.com/CVE-2024-22660/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-3666 and fix it if it is affected.

What it is: CVE-2025-3666 is a medium-severity missing authorization vulnerability in TOTOLINK A3700R, published on 16 Apr 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-2025-3666 exists.

Affected product: TOTOLINK A3700R. 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-2025-3666/ (Markdown: https://insights.sbomify.com/CVE-2025-3666/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-3666
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-3666
- OSV: https://osv.dev/vulnerability/CVE-2025-3666

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-3666/
Summaries are generated and may contain mistakes; the official description above is the record.