CVE-2020-12521
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 · uneditedOn Phoenix Contact PLCnext Control Devices versions before 2021.0 LTS a specially crafted LLDP packet may lead to a high system load in the PROFINET stack. An attacker can cause failure of system services or a complete reboot.
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 confidenceA specially crafted LLDP (Link Layer Discovery Protocol) packet causes excessive system load in the PROFINET stack of Phoenix Contact PLCnext Control devices versions prior to 2021.0 LTS. The malformed packet triggers a denial of service condition that can cause system services to fail or force a complete device reboot.
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< 2021.0CVSS 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
- Adjacent
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:A/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 modelConfirm the target device is a Phoenix Contact PLCnext Control PLC (such as AXC F 1150, AXC F 2150, or RFC 4072S). Check the device label, web interface, or CLI output.Affected if The device is a Phoenix Contact PLCnext Control device.
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Check firmware versionAccess the PLCnext web interface (typically at https://<device-ip>) and navigate to System > Firmware or use the PLCnext CLI command 'plcncli get device-info' to retrieve the installed firmware version.Affected if The firmware version is earlier than 2021.0 LTS (e.g., 2020.x, 2019.x, or earlier).
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Verify LLDP protocol is enabledCheck the network configuration via the PLCnext web interface under Network > LLDP or use the CLI command 'lldpctl' or 'show lldp' to determine if Link Layer Discovery Protocol is enabled.Affected if LLDP is enabled and processing incoming LLDP packets on the network.
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Confirm PROFINET stack is in useVerify PROFINET functionality is active on the device by checking the project configuration in PLCnext Engineer software or by examining running services via CLI with 'systemctl list-units | grep profinet' or inspecting the device web interface for PROFINET modules.Affected if PROFINET stack is running or configured in the project.
The device is affected if it is a Phoenix Contact PLCnext Control with firmware version earlier than 2021.0 LTS, has LLDP enabled, and has the PROFINET stack active or configured.
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 data2021.0
Update Phoenix Contact PLCnext Control devices to firmware version 2021.0 LTS or later to patch the vulnerability. If immediate patching is not possible, consider network segmentation to restrict LLDP traffic to trusted sources only.
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-12521 — 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-2020-12521 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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