CVE-2015-3938
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 · uneditedThe HTTP application on Mitsubishi Electric MELSEC FX3G PLC devices before April 2015 allows remote attackers to cause a denial of service (device outage) via a long parameter.
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 confidenceThe Mitsubishi Electric MELSEC FX3G PLC devices contain a denial of service vulnerability in their built-in HTTP web server application. Remote attackers can send HTTP requests with excessively long parameters to trigger the device outage, causing the PLC to stop functioning.
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 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
- Authentication
- None
- Confidentiality
- None
- Integrity
- None
- Availability
- Complete
AV:N/AC:L/Au:N/C:N/I:N/A:C
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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Confirm MELSEC FX3G model numberLocate the PLC hardware model label or query the device via GX Works2 software to verify the exact model is FX3G seriesAffected if Device model is not MELSEC FX3G series - then not affected by this specific CVE
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Identify HTTP server statusAccess the PLC configuration via GX Works2 or check the PLC parameters for the built-in web server function. Navigate to the Ethernet port settings and verify if the HTTP server function is enabledAffected if HTTP server function is enabled and accessible on the network - device is vulnerable to the DoS condition
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Check network exposure of HTTP interfaceUse network scanning tools (such as nmap) to probe the PLC IP address on common HTTP ports 80 and 443. Verify if the web management interface responds to HTTP requestsAffected if HTTP port is open and responds to requests from network segments outside the local control network - attack surface exists
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Verify firmware versionConnect to the PLC via GX Works2 and read the device firmware version from the CPU module information, or access the HTTP web page and check the firmware version displayedAffected if Firmware is any version - all versions of FX3G are affected according to the advisory
If the device is a MELSEC FX3G with the built-in HTTP web server enabled and network-accessible, the environment is affected by this CVE and could be disrupted by specially crafted HTTP requests with oversized parameters.
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 dataUpdate the MELSEC FX3G firmware to the April 2015 or later release. Additionally, restrict network access to the HTTP management interface using firewalls or VLANs to prevent unauthorized attackers from reaching the PLC.
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2015-3938 — 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-2015-3938 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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