CVE-2021-27561
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedYealink Device Management (DM) 3.6.0.20 allows command injection as root via the /sm/api/v1/firewall/zone/services URI, without authentication.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceYealink Device Management 3.6.0.20 contains a critical command injection vulnerability in the /sm/api/v1/firewall/zone/services API endpoint. The lack of authentication allows remote attackers to inject and execute arbitrary OS commands with root privileges.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data<= 3.6.0.20CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify if Yealink Device Management is runningCheck for processes or services named 'yealink', 'dm', or 'device management' running on the server. Look for the web service on common ports like 80, 443, or 8080.Affected if The Yealink DM web service is running and accessible on the network.
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Determine the installed Yealink DM versionAccess the web interface and check the version information typically found in the admin panel, about page, or footer. Alternatively, check the application's binaries, configuration files, or package metadata for version 3.6.0.20 or lower.Affected if The installed version is 3.6.0.20 or any earlier version.
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Verify the vulnerable API endpoint existsSend an HTTP request to the /sm/api/v1/firewall/zone/services endpoint on the server (e.g., GET https://target:port/sm/api/v1/firewall/zone/services). Check if the endpoint responds or requires authentication.Affected if The endpoint responds to unauthenticated requests, indicating it is accessible without login.
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Confirm pre-authentication accessAttempt to access the API endpoint without providing any authentication credentials (no cookies, tokens, or Basic Auth). Observe whether the request is accepted or rejected.Affected if The endpoint accepts requests without any authentication and returns a response rather than a 401/403 error.
You are affected if Yealink Device Management version 3.6.0.20 or lower is installed AND the /sm/api/v1/firewall/zone/services endpoint is accessible without authentication.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataApply the vendor security update for Yealink DM. Until patched, restrict network access to the management interface using firewall rules or network segmentation.
- Consultation4.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,448.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-27561 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-27561 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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