CVE-2021-31890
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 · uneditedA vulnerability has been identified in Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R20-11 (All versions < V2303), PLUSCONTROL 1st Gen (All versions), SIMOTICS CONNECT 400 (All versions < V0.5.0.0), SIMOTICS CONNECT 400 (All versions < V1.0.0.0). The total length of an TCP payload (set in the IP header) is unchecked. This may lead to various side effects, including Information Leak and Denial-of-Service conditions, depending on the network buffer organization in memory. (FSMD-2021-0017)
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 confidenceThe vulnerability stems from missing validation of the IP header Total Length field against the actual TCP payload received. When a crafted packet with a mismatched length is processed, the system may read beyond the actual packet data into adjacent memory (information disclosure) or cause buffer processing errors leading to denial of service. This affects embedded industrial network stack implementations.
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 dataall versionsall versions< 2017.02.4< 4.1.1all versionsall versionsall versionsall versionsCVSS 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
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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 exact product and firmware versionLocate the device model number and firmware version through the device's web interface, console, or hardware labeling. For Siemens devices, this is typically found in the system information or management interface.Affected if The product matches any of the affected products listed: Capital Vstar, Nucleus Net, Nucleus Readystart V3 (< 2017.02.4), Nucleus Readystart V4 (< 4.1.1), Nucleus Source Code, Apogee Modular Building Controller, Apogee Modular Equipment Controller, or Apogee PXC Compact Firmware.
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Check Nucleus network stack implementationDetermine if the device uses the Nucleus IP stack for network packet processing. This may require reviewing product documentation, firmware analysis, or contacting the vendor for architecture confirmation.Affected if The device implements the Nucleus network stack for TCP/IP packet handling.
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Verify IP packet handling configurationExamine network configuration or packet capture setup to observe how the device processes incoming IP packets. Look for any built-in packet validation features or logging of malformed packets.Affected if The device processes raw IP packets without validating the Total Length field against the actual payload size.
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Monitor for malformed IP packetsUse network capture tools (such as tcpdump, Wireshark, or industrial network monitors) to inspect incoming traffic for IP packets where the Total Length header field does not match the actual data received.Affected if The device accepts and processes IP packets with mismatched Total Length fields without rejecting them.
The environment is affected if any Siemens device is running a firmware version within the affected ranges (Nucleus Readystart V3 < 2017.02.4, V4 < 4.1.1) or if any listed product uses the Nucleus IP stack for packet processing without additional packet validation layers.
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 data4.1.12017.02.4
Apply vendor-supplied firmware patches for affected products (Capital Embedded AR Classic, PLUSCONTROL 1st Gen, SIMOTICS CONNECT 400). Until patches are available, isolate affected devices behind firewalls with strict packet validation or employ network intrusion detection to flag malformed IP packets.
- Consultation8.0 h
- Implementation16.0 h
- Testing12.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-31890 — 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-2021-31890 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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