CVE-2021-21004
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 · uneditedIn Phoenix Contact FL SWITCH SMCS series products in multiple versions an attacker may insert malicious code via LLDP frames into the web-based management which could then be executed by the client.
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 · moderate confidenceThe FL SWITCH SMCS series network switches do not properly sanitize LLDP (Link Layer Discovery Protocol) frames before incorporating their data into the web-based management interface. An attacker on the same network segment can send crafted LLDP frames containing malicious code (likely JavaScript). When administrative users later access the switch's web interface, this injected code executes in their browser context, enabling session hijacking or further client-side attacks.
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<= 4.70<= 4.70<= 4.70<= 4.70<= 4.70<= 4.70<= 4.70<= 4.70CVSS 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
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
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 the exact switch modelLog into the switch web interface or CLI and retrieve the model name from the device status or system information page. Match it against the affected product list: FL SWITCH SMCS 16tx, 14tx/2fx, 14tx/2fx SM, 8gt, 6gt/2sfp, 8tx PN, 4tx PN, or 8tx.Affected if The switch model is any of the listed FL SMCS series variants.
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Check the installed firmware versionIn the web interface, navigate to System > Firmware or System > Information to view the current firmware version. Compare it to the affected range: any version <= 4.70.Affected if The firmware version is 4.70 or lower.
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Verify LLDP protocol statusIn the web interface, go to Layer 2 > LLDP or Administration > LLDP settings. Confirm whether LLDP is enabled on the switch.Affected if LLDP is enabled and the switch is on the same network segment with untrusted devices.
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Confirm web-based management is accessibleAttempt to reach the switch web interface via HTTP/HTTPS from a browser. Note that the XSS payload executes when an administrative user views the LLDP information page in the web interface.Affected if The web management interface is accessible and the switch processes incoming LLDP frames.
The switch is affected if it is an FL SWITCH SMCS series model running firmware version 4.70 or lower with LLDP enabled and the web management interface in use.
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 dataRestrict network access to the management interface and disable LLDP on untrusted segments; apply vendor firmware updates when available. Monitor for anomalous LLDP traffic on industrial network segments.
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-21004 — 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-2021-21004 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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- 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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