# CVE-2021-27561: Yealink Device Management Server-Side Request Forgery (SSRF)

> Unauthenticated attackers can execute arbitrary commands as root on Yealink Device Management systems via a specific API endpoint.

- **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:** Yes, since 3 Nov 2021 (CISA KEV)
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Oct 2021
- **Updated:** 21 Oct 2025
- **Also known as:** GHSA-743m-83p4-9349

## What is CVE-2021-27561?

CVE-2021-27561 is a critical command injection vulnerability in n/a, published on 15 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Yealink Device Management (DM) 3.6.0.20 allows command injection as root via the /sm/api/v1/firewall/zone/services URI, without authentication.

Weakness: CWE-78 (Improper Neutralization of Special Elements used in an OS Command)

## Which versions are affected by CVE-2021-27561?

It affects 1 product.


Products: Yealink Device Management.

## How do I fix CVE-2021-27561?

No fix has been published for CVE-2021-27561 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 17 Nov 2021.

## Is CVE-2021-27561 being exploited?

Yes. Attackers have exploited CVE-2021-27561 in the wild since at least 3 Nov 2021.

Public exploit code:

- YeaLink DM 3.6.0.20 - Remote Command Injection (nuclei): http/cves/2021/CVE-2021-27561.yaml

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-27561 and fix it if it is affected.

What it is: CVE-2021-27561 is a critical command injection vulnerability in n/a, published on 15 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2021-27561 in the wild since at least 3 Nov 2021.

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-2021-27561/ (Markdown: https://insights.sbomify.com/CVE-2021-27561/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-27561
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-27561
- OSV: https://osv.dev/vulnerability/CVE-2021-27561

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-27561/
Summaries are generated and may contain mistakes; the official description above is the record.