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Melsec Iq R R00 Cpu FirmwareOperating system · Mitsubishi

CVE-2021-20609

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
Uncontrolled Resource Consumption 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

Mitsubishi Electric MELSEC PLCs (iQ-R, Q, L Series, and MI5122-VW) contain an uncontrolled resource consumption vulnerability where specially crafted packets from a remote unauthenticated attacker can exhaust resources and cause a denial-of-service condition, requiring a system reset for recovery.

MitigationImplement network segmentation and firewalls to restrict unauthorized access to the PLCs; check with Mitsubishi Electric for firmware updates and apply if available; monitor network traffic for anomalous patterns indicative of the attack.

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 the PLC model and series
    Access the PLC hardware label or use engineering software (e.g., GX Works3) to query the PLC CPU module part number. Look for model numbers such as R00CPU, R01CPU, R02CPU, R04CPU, R08CPU, R120CPU, R16CPU, or R32CPU which indicate iQ-R series units.
    Affected if The PLC is an iQ-R series CPU module (R00, R01, R02, R04, R08, R120, R16, or R32)
  2. Determine the firmware version
    Connect to the PLC using GX Works3 engineering software. Navigate to the CPU module diagnostics or system information section to read the firmware version. Alternatively, check the firmware version sticker on the physical CPU module.
    Affected if The firmware version is at or below 24 for R00/R01/R02 CPUs, or at or below 57 for R04/R08/R120/R16/R32 CPUs
  3. Verify network communication is enabled
    Check the PLC configuration in GX Works3 under the Ethernet port settings. Confirm that the built-in Ethernet function or any MELSEC protocol communication is configured and enabled.
    Affected if Ethernet communication is enabled on the PLC (this is the default operational state and the attack surface)

A user is affected if they operate an iQ-R series PLC (R00/R01/R02 with firmware <=24, or R04/R08/R120/R16/R32 with firmware <=57) with network communication enabled, as the vulnerability is triggered by specially crafted packets received over the network.

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

Implement network segmentation and firewalls to restrict unauthorized access to the PLCs; check with Mitsubishi Electric for firmware updates and apply if available; monitor network traffic for anomalous patterns indicative of the attack.

Fix this in Melsec Iq R R00 Cpu Firmware Scoped from the published advisory
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing8.0 h
  • Review / QA4.0 h
36.0 hours of engineering $6,400
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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-2021-20609 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