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Cr800 Q FirmwareOperating system · Mitsubishielectric

CVE-2020-5527

HIGH · 7.5 CVSS v3.1 Published 2020-03-30
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
When MELSOFT transmission port (UDP/IP) of Mitsubishi Electric MELSEC iQ-R series (all versions), MELSEC iQ-F series (all versions), MELSEC Q series (all versions), MELSEC L series (all versions), and MELSEC F series (all versions) receives massive amount of data via unspecified vectors, resource consumption occurs and the port does not process the data properly. As a result, it may fall into a denial-of-service (DoS) condition. The vendor states this vulnerability only affects Ethernet communication functions.

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 confidence

A denial-of-service vulnerability in Mitsubishi Electric MELSEC PLCs (iQ-R, iQ-F, Q, L, F series) where the MELSOFT UDP transmission port becomes unresponsive when receiving excessive data, causing resource consumption that prevents proper data processing.

MitigationImplement network segmentation and firewalls to restrict unauthorized traffic to the MELSOFT UDP port; consider disabling Ethernet communication functions if not required, pending vendor firmware patch.

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
Cr800 Q FirmwareOperating system
Affected:all versions
Fx3g FirmwareOperating system
Affected:all versions
Fx3gc FirmwareOperating system
Affected:all versions
Fx3s FirmwareOperating system
Affected:all versions
Fx3u FirmwareOperating system
Affected:all versions
Fx3uc FirmwareOperating system
Affected:all versions
Fx5u FirmwareOperating system
Affected:all versions
Fx5uc FirmwareOperating system
Affected:all versions

CVSS 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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify PLC model and firmware version
    Access the PLC programming software (GX Works2, GX Works3, or GX Developer) and connect to the PLC. Navigate to the PLC diagnostics or system information to retrieve the model name and firmware version. Alternatively, check the physical PLC unit label for model number and series.
    Affected if The PLC model matches any of these: Cr800 Q, Fx3g, Fx3gc, Fx3s, Fx3u, Fx3uc, Fx5u, Fx5uc (or other iQ-R, iQ-F, Q, L, F series variants)
  2. Verify Ethernet communication is enabled
    In the PLC programming software, open the PLC parameter settings. Navigate to the Ethernet port configuration or built-in Ethernet settings. Check if the Ethernet communication function is set to 'Use' or enabled.
    Affected if Ethernet communication functions are enabled in the PLC configuration
  3. Confirm MELSOFT UDP port is active
    In the PLC parameter settings under Ethernet configuration, locate the MELSOFT connection settings or UDP communication settings. Verify if MELSOFT UDP transmission is configured and active. Common ports include 5006 and 5007, but check your specific model documentation.
    Affected if MELSOFT UDP transmission port is configured and active
  4. Check network exposure of UDP ports
    Use network scanning tools (such as nmap) from a system on the same network to scan the PLC IP address for open UDP ports. Example: nmap -sU -p 5006,5007 <PLC_IP_ADDRESS>. Alternatively, check firewall rules or network segmentation devices.
    Affected if The PLC's UDP ports (particularly MELSOFT ports) are exposed to untrusted networks or accessible from unauthorized systems

Your environment is affected if you have any of the listed PLC models (Cr800 Q, Fx3g, Fx3gc, Fx3s, Fx3u, Fx3uc, Fx5u, Fx5uc or related iQ-R/iQ-F/Q/L/F series) with Ethernet and MELSOFT UDP communication enabled, and those ports are reachable from networks where excessive unsolicited UDP traffic could be sent.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Implement network segmentation and firewalls to restrict unauthorized traffic to the MELSOFT UDP port; consider disabling Ethernet communication functions if not required, pending vendor firmware patch.

Fix this in Cr800 Q Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-5527 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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