CVE-2021-21005
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 if an attacker sends a hand-crafted TCP-Packet with the Urgent-Flag set and the Urgent-Pointer set to 0, the network stack will crash. The device needs to be rebooted afterwards.
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 confidenceIn Phoenix Contact FL SWITCH SMCS series products, a specially crafted TCP packet with the Urgent-Flag set and Urgent-Pointer set to 0 triggers a network stack crash. The affected device requires a manual reboot to restore functionality.
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
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 the device modelLocate the physical device label or check the web interface (System > Information) to confirm the exact model number matches one of: FL SWITCH SMCS 16tx, 14tx/2fx, 14tx/2fx SM, 8gt, 6gt/2sfp, 8tx PN, 4tx PN, or 8txAffected if The device model is any of the listed affected models
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Check the installed firmware versionAccess the device web interface and navigate to System > Firmware or use the console and run the appropriate firmware version command; compare the version number against the affected rangeAffected if Firmware version is 4.70 or lower
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Verify network exposure of the management interfaceReview firewall rules and network segmentation to determine if the device management interface (typically ports 80/443 or SNMP) is accessible from untrusted networks or the internetAffected if The management interface is reachable from untrusted networks without firewall protection
You are affected if your device is one of the listed FL SWITCH SMCS models running firmware version 4.70 or lower, and the device is network-accessible to potential attackers.
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 vendor-released firmware patches to address this vulnerability. If patching is immediately impractical, restrict network access to the affected devices using firewalls or network segmentation to limit exposure to unauthenticated attackers.
- Consultation2.0 h
- Implementation3.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,272.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-21005 — 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-2021-21005 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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