CVE-2020-7539
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 CWE-754 Improper Check for Unusual or Exceptional Conditions vulnerability exists in the Web Server on Modicon M340, Legacy Offers Modicon Quantum and Modicon Premium and associated Communication Modules (see security notification for affected versions), that could cause a denial of service vulnerability when a specially crafted packet is sent to the controller over HTTP.
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 CWE-754 Improper Check for Unusual or Exceptional Conditions vulnerability exists in the Web Server component of Schneider Electric Modicon M340, Legacy Modicon Quantum and Modicon Premium PLCs, where a specially crafted HTTP packet triggers an unhandled exception causing denial of service.
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< 3.30< 3.30< 3.30< 3.30< 3.30< 3.30< 3.30< 3.3CVSS 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 Modicon device modelAccess the PLC through its management interface or check the physical device label for the model number (Bmxp341000, Bmxp342000, Bmxp3420102, Bmxp3420102cl, Bmxp342020, Bmxp3420302, Bmxp3420302cl, or Bmxnoe0100)Affected if The device model is any of these eight variants: Bmxp341000, Bmxp342000, Bmxp3420102, Bmxp3420102cl, Bmxp342020, Bmxp3420302, Bmxp3420302cl, or Bmxnoe0100
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Check the installed firmware versionUse the PLC programming software (Unity Pro or EcoStruxure) or access the device web interface to view the firmware version informationAffected if The firmware version is less than 3.30 (or less than 3.3 for the Bmxnoe0100)
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Verify the Web Server is enabledAccess the PLC configuration settings through the programming software or web interface and check the Web Server / HTTP server statusAffected if The Web Server component is enabled and accessible via HTTP
The device is affected if it is a listed Modicon M340 model (Bmxp341000, Bmxp342xxx series) or Bmxnoe0100, running firmware below version 3.30, with the Web Server feature enabled and accessible.
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 data3.33.30
Isolate affected devices behind a firewall or air-gap, block HTTP access from untrusted networks, and consider disabling the web server if not operationally required.
- Consultation4.0 h
- Implementation8.0 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-2020-7539 — 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-2020-7539 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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