CVE-2021-27561 — Yealink Device Management Server-Side Request Forgery (SSRF) Vulnerability

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

01What is this vulnerability?

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

02Affected products

Vendor	Product	Versions
n	a / n/a	n/a

03Active exploitation status

Yes — actively exploited. Added to the CISA KEV catalog on 2021-11-03. Ransomware use: Unknown.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Open the Sigma generator with a pre-filled prompt for this CVE to draft a starting detection in your stack of choice:

Open in Sigma generator →

07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2021-10-15T17:11:45.000Z
• Last modified: 2025-10-21T23:25:28.403Z
• Added to CISA KEV: 2021-11-03
• BOD 22-01 due: 2021-11-17

09References

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