dbcve.org
Melsec Iq R00 FirmwareOperating system · Mitsubishielectric

CVE-2020-5666

HIGH · 7.5 CVSS v3.1 Published 2020-11-16
Fix available
A fix is available. Upgrade to after 51 or later.
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
Uncontrolled resource consumption vulnerability in MELSEC iQ-R Series CPU Modules (R00/01/02CPU Firmware versions from '05' to '19' and R04/08/16/32/120(EN)CPU Firmware versions from '35' to '51') allows a remote attacker to cause an error in a CPU unit via a specially crafted HTTP packet, which may lead to a denial-of-service (DoS) condition in execution of the program and its communication.

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

Uncontrolled resource consumption vulnerability in Mitsubishi MELSEC iQ-R Series PLC CPU modules allows remote attackers to send specially crafted HTTP packets that cause CPU errors, leading to denial of service. Affected firmware versions are R00/01/02CPU (versions 05-19) and R04/08/16/32/120(EN)CPU (versions 35-51). The vulnerability is in the HTTP communication handling component.

MitigationUpdate CPU module firmware to versions beyond 19 (for R00/01/02CPU) or 51 (for R04/08/16/32/120(EN)CPU). If immediate patching is not feasible, implement network segmentation and firewall rules to restrict HTTP access to the PLCs, and monitor for anomalous HTTP traffic patterns.

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
Melsec Iq R00 FirmwareOperating system
Affected:>= 05, <= 19
Melsec Iq R01 FirmwareOperating system
Affected:>= 05, <= 19
Melsec Iq R02 FirmwareOperating system
Affected:>= 05, <= 19
Melsec Iq R04 FirmwareOperating system
Affected:>= 35, <= 51
Melsec Iq R16 FirmwareOperating system
Affected:>= 35, <= 51
Melsec Iq R08 FirmwareOperating system
Affected:>= 35, <= 51
Melsec Iq R32 FirmwareOperating system
Affected:>= 35, <= 51
Melsec Iq R120 FirmwareOperating system
Affected:>= 35, <= 51

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
    Locate the CPU module model number on the physical device label or in the project metadata using GX Works3 engineering software. Confirm it is one of: R00CPU, R01CPU, R02CPU, R04CPU, R08CPU, R16CPU, R32CPU, or R120(EN)CPU.
    Affected if Model is any R00/01/02/04/08/16/32/120(EN)CPU variant
  2. Check firmware version
    Access the CPU module firmware version via GX Works3 by connecting to the PLC and viewing the CPU module information, or through the web-based management interface if enabled.
    Affected if Firmware version is 05-19 for R00/01/02CPU, OR 35-51 for R04/08/16/32/120(EN)CPU
  3. Verify HTTP communication is enabled
    In GX Works3, navigate to the module configuration and check the HTTP server settings. Confirm whether the built-in HTTP communication function is activated in the network configuration.
    Affected if HTTP communication function is enabled on the affected CPU module
  4. Check network accessibility of HTTP service
    Perform a port scan or review firewall rules to determine if HTTP ports (default 80/443) on the PLC are accessible from network segments outside the trusted control system network.
    Affected if HTTP service on the PLC is exposed to untrusted network segments

The environment is affected if the PLC model is a vulnerable MELSEC iQ-R CPU variant, the firmware version falls within the affected ranges (05-19 for R00/01/02, 35-51 for R04/08/16/32/120), and HTTP communication is enabled and accessible.

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
Upgrade available Upgrade to a release after 51
Interim mitigation

Update CPU module firmware to versions beyond 19 (for R00/01/02CPU) or 51 (for R04/08/16/32/120(EN)CPU). If immediate patching is not feasible, implement network segmentation and firewall rules to restrict HTTP access to the PLCs, and monitor for anomalous HTTP traffic patterns.

Fix this in Melsec Iq R00 Firmware Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
30.0 hours of engineering $5,280
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $8,448.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2020-5666 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2020-5666 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data