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Melsec Iq Rj71eip91 FirmwareOperating system · Mitsubishielectric

CVE-2020-5655

HIGH · 7.5 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 →
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
NULL pointer dereferences 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 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

This is a NULL pointer dereference vulnerability in the TCP/IP function of the firmware for multiple Mitsubishi MELSEC iQ-R series modules (RJ71EIP91, RJ71PN92, RD81DL96, RD81MES96N, RD81OPC96). A remote unauthenticated attacker can send specially crafted packets to trigger the NULL pointer dereference, causing the network functions of the affected devices to stop, resulting in denial of service.

MitigationApply the vendor-provided firmware updates corresponding to the affected serial numbers. If immediate patching is not possible, isolate affected devices behind firewalls or implement network segmentation to reduce exposure to unauthenticated attackers.

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
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 device model
    Locate the physical module or check the system configuration to confirm the exact model number of the MELSEC iQ-R series module
    Affected if The model is RJ71EIP91, RJ71PN92, RD81DL96, RD81MES96N, or RD81OPC96
  2. Verify network function is enabled
    Check the module configuration or system settings to confirm the TCP/IP or network communication function is enabled on the affected device
    Affected if Network functions are enabled and the device is one of the affected models
  3. Confirm network accessibility
    Test if the device is reachable on the network via ping or by attempting to access its web interface or open ports associated with the module's network services
    Affected if The affected device is directly accessible from network segments accessible to unauthenticated users
  4. Check for network function failure
    Monitor the device or PLC system for loss of network communication, failed ping responses, or inability to access the module remotely
    Affected if Network functions have stopped responding and the device is one of the affected models

If you have any of the affected models (RJ71EIP91, RJ71PN92, RD81DL96, RD81MES96N, RD81OPC96) with network functions enabled and directly accessible, your environment is affected by this vulnerability.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the vendor-provided firmware updates corresponding to the affected serial numbers. If immediate patching is not possible, isolate affected devices behind firewalls or implement network segmentation to reduce exposure to unauthenticated attackers.

Fix this in Melsec Iq Rj71eip91 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-2020-5655 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
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  • Version or environment caveats, and links to real fixes
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