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Melsec Iq R R00 Cpu FirmwareOperating system · Mitsubishi

CVE-2021-20611

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 Input Validation 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

Improper input validation vulnerability in Mitsubishi Electric MELSEC iQ-R and Q Series PLCs allows remote unauthenticated attackers to cause denial-of-service by sending specially crafted packets. The vulnerability stems from insufficient validation of incoming network communications, leading to a system crash that requires manual reset for recovery.

MitigationApply vendor patches when available. Until patches are applied, implement network segmentation and firewall rules to restrict unauthorized access to affected PLCs, and monitor for anomalous network 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 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 PLCs in your environment
    Inventory network devices and verify if any Mitsubishi MELSEC iQ-R Series PLCs (CPU models R00, R01, R02, R04, R08, R120, R16, R32) are present on the network
    Affected if MELSEC iQ-R PLCs are present in the network inventory
  2. Determine the CPU model number
    Access the PLC configuration via GX Works3 engineering software or check the physical PLC unit label to identify the exact CPU model (R00, R01, R02, R04, R08, R120, R16, or R32)
    Affected if The CPU model is one of: R00, R01, R02, R04, R08, R120, R16, or R32
  3. Check the installed firmware version
    Connect to the PLC via GX Works3, navigate to CPU module diagnostics, and read the firmware version from the product information or system information screen
    Affected if Firmware version is <= 24 for R00/R01/R02, or <= 57 for R04/R08/R120/R16/R32 (or 'all versions' is listed for that model)
  4. Verify network communication is enabled
    Check the PLC network configuration in GX Works3 under the Ethernet/TCP-IP settings to confirm the PLC has an active IP address and network communication module is configured
    Affected if The PLC has an active network interface and is reachable over Ethernet
  5. Confirm network accessibility
    Ping the PLC IP address or attempt a TCP connection to common industrial protocol ports (such as 5002 for MELSEC, or as configured) to verify the PLC is network-accessible from your workstations
    Affected if The PLC responds to network requests and is accessible from your operational network

Your environment is affected if you have a MELSEC iQ-R PLC (R00, R01, R02, R04, R08, R120, R16, or R32) with firmware at or below the listed version threshold AND the PLC is network-connected 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 57
Interim mitigation

Apply vendor patches when available. Until patches are applied, implement network segmentation and firewall rules to restrict unauthorized access to affected PLCs, and monitor for anomalous network traffic patterns.

Fix this in Melsec Iq R R00 Cpu 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
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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-2021-20611 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