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Melsec Iq R R00 Cpu FirmwareOperating system · Mitsubishi

CVE-2021-20610

HIGH · 7.5 CVSS v3.1 Published 2021-12-01
Fix available
A fix is available. Upgrade to after 57 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
Improper Handling of Length Parameter Inconsistency vulnerability in Mitsubishi Electric MELSEC iQ-R Series R00/01/02CPU, MELSEC iQ-R Series R04/08/16/32/120(EN)CPU, MELSEC iQ-R Series R08/16/32/120SFCPU, MELSEC iQ-R Series R08/16/32/120PCPU, MELSEC iQ-R Series R08/16/32/120PSFCPU, MELSEC iQ-R Series R16/32/64MTCPU, MELSEC iQ-R Series R12CCPU-V, MELSEC Q Series Q03UDECPU, MELSEC Q Series Q04/06/10/13/20/26/50/100UDEHCPU, MELSEC Q Series Q03/04/06/13/26UDVCPU, MELSEC Q Series Q04/06/13/26UDPVCPU, MELSEC Q Series Q12DCCPU-V, MELSEC Q Series Q24DHCCPU-V(G), MELSEC Q Series Q24/26DHCCPU-LS, MELSEC Q Series MR-MQ100, MELSEC Q Series Q172/173DCPU-S1, MELSEC Q Series Q172/173DSCPU, MELSEC Q Series Q170MCPU, MELSEC Q Series Q170MSCPU(-S1), MELSEC L Series L02/06/26CPU(-P), MELSEC L Series L26CPU-(P)BT and MELIPC Series MI5122-VW allows a remote unauthenticated attacker to cause a denial-of-service (DoS) condition by sending specially crafted packets. System reset is required for recovery.

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

This is a length parameter inconsistency vulnerability in Mitsubishi Electric PLCs (MELSEC iQ-R, Q, L series and MI5122-VW) where the devices improperly handle packet length parameters. A remote unauthenticated attacker can send specially crafted packets that cause the PLC to enter a denial-of-service condition, requiring a physical system reset to recover.

MitigationApply vendor-supplied firmware updates when available. In the interim, implement network segmentation to restrict access to affected PLCs and deploy firewall rules to filter potentially malicious packets targeting industrial protocols.

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 R R00 Cpu FirmwareOperating system
Affected:<= 24
Melsec Iq R R01 Cpu FirmwareOperating system
Affected:<= 24
Melsec Iq R R02 Cpu FirmwareOperating system
Affected:<= 24
Melsec Iq R R04 Cpu FirmwareOperating system
Affected:<= 57
Melsec Iq R R08 Cpu FirmwareOperating system
Affected:<= 57all versions
Melsec Iq R R120 Cpu FirmwareOperating system
Affected:<= 57all versions
Melsec Iq R R16 Cpu FirmwareOperating system
Affected:<= 57all versions
Melsec Iq R R32 Cpu FirmwareOperating system
Affected:<= 57all 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 MELSEC iQ-R PLC models in the environment
    Review engineering workstation project files, network scans, or PLC hardware labels to determine if models R00, R01, R02, R04, R08, R120, R16, or R32 are present
    Affected if The model is any of: R00, R01, R02, R04, R08, R120, R16, or R32 CPU
  2. Check PLC firmware version
    Connect to the PLC via GX Works3 or access the PLC's system information menu to retrieve the firmware version number
    Affected if Firmware version is <= 24 for R00/R01/R02, or <= 57 for R04/R08/R120/R16/R32
  3. Verify network accessibility of the PLC
    Ping the PLC IP address or perform a port scan on common industrial protocol ports (such as UDP 5006/5007 for MELSEC) to confirm the PLC is reachable over the network
    Affected if The PLC is directly accessible from untrusted network segments
  4. Check for denial-of-service symptoms
    Attempt to access the PLC via GX Works3 or check if the PLC RUN/STOP LED is unresponsive or the PLC is not communicating on the network
    Affected if PLC is unresponsive, cannot establish communication, or shows no LED activity indicating a DoS state

If the PLC is a MELSEC iQ-R model (R00/R01/R02/R04/R08/R120/R16/R32) with firmware at or below the affected version threshold and is network-accessible, the environment is vulnerable to CVE-2021-20610.

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 57
Interim mitigation

Apply vendor-supplied firmware updates when available. In the interim, implement network segmentation to restrict access to affected PLCs and deploy firewall rules to filter potentially malicious packets targeting industrial protocols.

Fix this in Melsec Iq R R00 Cpu Firmware Scoped from the published advisory
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing12.0 h
  • Review / QA4.0 h
40.0 hours of engineering $7,000
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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-2021-20610 in production — separate from our analysis above.

No notes yet

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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