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Melsec Iq Rj71eip91 FirmwareOperating system · Mitsubishielectric

CVE-2020-5656

CRITICAL · 9.8 CVSS v3.1 Published 2020-11-02
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
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 access control vulnerability in TCP/IP function included in the firmware of MELSEC iQ-R series (RJ71EIP91 EtherNet/IP Network Interface Module First 2 digits of serial number are '02' or before, RJ71PN92 PROFINET IO Controller Module First 2 digits of serial number are '01' or before, RD81DL96 High Speed Data Logger Module First 2 digits of serial number are '08' or before, RD81MES96N MES Interface Module First 2 digits of serial number are '04' or before, and RD81OPC96 OPC UA Server Module First 2 digits of serial number are '04' or before) allows a remote unauthenticated attacker to stop the network functions of the products or execute a malicious program via a specially crafted packet.

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 access control in the TCP/IP function of MELSEC iQ-R series firmware allows remote unauthenticated attackers to send specially crafted packets that can either stop network functions (DoS) or execute malicious code (RCE). The vulnerability affects multiple network interface modules including EtherNet/IP, PROFINET IO, and OPC UA servers, identified by serial number prefixes.

MitigationUpdate firmware to versions that address the serial number threshold requirements. Until patches are applied, restrict network access to affected modules using firewalls or network segmentation to limit exposure to untrusted networks.

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 Rj71eip91 FirmwareOperating system
Affected:all versions
Melsec Iq Rj71pn92 FirmwareOperating system
Affected:all versions
Melsec Iq Rd81dl96 FirmwareOperating system
Affected:all versions
Melsec Iq Rd81mes96n FirmwareOperating system
Affected:all versions
Melsec Iq Rd81opc96 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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 installed MELSEC iQ-R network modules
    Check the system hardware configuration or PLC project settings for presence of RJ71EIP91, RJ71PN92, RD81DL96, RD81MES96N, or RD81OPC96 modules
    Affected if Any of these five module model numbers are present in the system configuration
  2. Verify network protocol configuration
    Access the module configuration via GX Works3 or the module's web interface and check if EtherNet/IP, PROFINET IO, or OPC UA server features are enabled
    Affected if Any of these network interface features are configured and active on the affected module
  3. Check module firmware version
    Connect to the module via GX Works3 or web browser and retrieve the firmware version from the module information screen
    Affected if The module firmware version is any version (all versions of these modules are affected)
  4. Assess network exposure
    Review network firewall rules and segmentation to determine if the affected module's network interface is accessible from untrusted networks
    Affected if The module's TCP/IP network interface is reachable from networks outside the trusted control system network

The environment is affected if any of the five vulnerable module models (RJ71EIP91, RJ71PN92, RD81DL96, RD81MES96N, RD81OPC96) are installed with network functions enabled and accessible from 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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Update firmware to versions that address the serial number threshold requirements. Until patches are applied, restrict network access to affected modules using firewalls or network segmentation to limit exposure to untrusted networks.

Recommended fix Moderate confidence

Contact vendor for latest firmware version

  1. Contact Mitsubishi Electric technical support to obtain the latest firmware version for your specific module
  2. Verify the serial number of your affected module to determine if it falls within the affected range (RJ71EIP91: serial prefix '02' or before, RJ71PN92: '01' or before, RD81DL96: '08' or before, RD81MES96N: '04' or before, RD81OPC96: '04' or before)
  3. Request and apply the firmware update from Mitsubishi Electric that addresses the improper access control vulnerability
  4. After updating, verify that network functions operate normally
  5. Implement network segmentation and firewall rules to limit exposure of the affected modules to untrusted networks as an additional protective measure
Caveat Firmware updates may require system downtime and should be tested in a non-production environment first

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Melsec Iq Rj71eip91 Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA3.0 h
21.0 hours of engineering $3,680
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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-2020-5656 in production — separate from our analysis above.

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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