CVE-2019-6857
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 Modicon M580, Modicon M340, Modicon Quantum, Modicon Premium (see security notification for specific versions) which could cause a Denial of Service of the controller when reading specific memory blocks using Modbus TCP.
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 confidenceThis is a CWE-754 vulnerability in Schneider Electric Modicon PLCs (M580, M340, Quantum, Premium) where improper handling of exceptional conditions during specific Modbus TCP memory read operations causes the controller to crash, resulting in 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< 2.80< 3.01< 3.20< 3.20< 3.20< 3.20< 3.20< 3.20CVSS 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 PLC modelCheck the physical device label, Unity Pro/EcoStruxure software project, or PLC runtime information to confirm the model is one of: Modicon M580, M340, Quantum, Premium, or the Tsx module variants (Tsxh5744m, Tsxh5724m, Tsxp576634m, Tsxp57554m, Tsxp575634m, Tsxp57454m)Affected if The device is any of the affected models listed in the CVE
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Determine the installed firmware versionAccess the PLC via its engineering software (Unity Pro, EcoStruxure Control Expert) or the PLC web server/Diagnostic pages to read the firmware version. Compare the version number against the affected ranges: M580 < 2.80, M340 < 3.01, Tsx modules < 3.20Affected if The firmware version is lower than 2.80 for M580, lower than 3.01 for M340, or lower than 3.20 for Tsx modules
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Verify Modbus TCP is enabledCheck the PLC configuration in the engineering software under Communication settings, or inspect the PLC network configuration to confirm Modbus TCP protocol is enabled on port 502Affected if Modbus TCP is enabled and accessible on the network
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Check network exposure of Modbus TCP serviceScan the network for open port 502 (Modbus TCP) or review firewall/network segmentation rules to determine if the PLC Modbus TCP service is reachable from untrusted network segmentsAffected if Port 502 is exposed to untrusted hosts or network segments beyond the trusted control network
You are affected if your PLC model and firmware version match an affected combination (M580 <2.80, M340 <3.01, or Tsx modules <3.20) AND Modbus TCP is enabled and accessible on your 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 data2.803.013.20
Apply available firmware patches from Schneider Electric; if unavailable, implement network segmentation and access controls to restrict Modbus TCP access to trusted hosts only.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,600.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2019-6857 — 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-2019-6857 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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