CVE-2021-36765
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 CODESYS EtherNetIP before 4.1.0.0, specific EtherNet/IP requests may cause a null pointer dereference in the downloaded vulnerable EtherNet/IP stack that is executed by the CODESYS Control runtime system.
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 confidenceA null pointer dereference vulnerability exists in the CODESYS EtherNet/IP stack versions prior to 4.1.0.0. Specific crafted EtherNet/IP requests sent to the CODESYS Control runtime system can trigger the vulnerability, causing the runtime to crash or become unstable due to the null pointer dereference in the downloaded EtherNet/IP stack.
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< 4.1.0.0CVSS 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
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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 if CODESYS Control runtime is installedCheck for CODESYS installation directories (typically under C:\Program Files\CODESYS or /opt/codesys) and look for Ethernetip.dll or similar EtherNet/IP stack files. Use system inventory tools or check installed programs list.Affected if CODESYS Control runtime with EtherNet/IP component is present on the system
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Determine installed EtherNet/IP stack versionLocate the Ethernetip.dll or related stack files within the CODESYS installation and check their file properties for version information, or query the CODESYS runtime for its component versions via the CODESYS Development System if available.Affected if The EtherNet/IP stack version is lower than 4.1.0.0
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Verify EtherNet/IP protocol is enabledCheck the CODESYS Control runtime configuration (typically in the PLC configuration file or CODESYS Control runtime settings) to confirm the EtherNet/IP adapter or stack is loaded and enabled for network communication.Affected if EtherNet/IP stack is loaded and actively handling network requests
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Confirm network exposure of the runtimeReview network configuration to determine if the CODESYS Control runtime EtherNet/IP listener is accessible from the network (check open ports and firewall rules for EtherNet/IP traffic on port 2222 or assigned ports).Affected if The runtime is reachable over the network and processing EtherNet/IP requests externally
The environment is affected if CODESYS Control runtime with an EtherNet/IP stack version below 4.1.0.0 is installed, the EtherNet/IP component is enabled, and the runtime is accessible over the network.
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 data4.1.0.0
Upgrade the CODESYS EtherNet/IP component to version 4.1.0.0 or later to obtain the vendor patch. If immediate upgrading is not feasible, restrict network access to the affected runtime and implement monitoring for anomalous EtherNet/IP traffic.
- Consultation6.0 h
- Implementation10.0 h
- Testing8.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-36765 — 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-2021-36765 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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- Version or environment caveats, and links to real fixes
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