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R08sfcpu FirmwareOperating system · Mitsubishielectric

CVE-2021-20598

MEDIUM · 5.3 CVSS v3.1 Published 2021-08-06
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
62/100
Remediation priority · Elevated
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
Overly Restrictive Account Lockout Mechanism vulnerability in Mitsubishi Electric MELSEC iQ-R series CPU modules (R08/16/32/120SFCPU all versions, R08/16/32/120PSFCPU all versions) allows a remote unauthenticated attacker to lockout a legitimate user by continuously trying login with incorrect password.

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

The MELSEC iQ-R series CPU modules have an overly restrictive account lockout mechanism that can be exploited by remote unauthenticated attackers. By repeatedly attempting logins with incorrect passwords, an attacker can trigger the lockout threshold and prevent legitimate users from accessing the device, causing a denial of service.

MitigationIsolate affected devices behind firewalls or in a protected network segment to limit exposure to unauthenticated attackers; implement rate-limiting or IP-based blocking at the network perimeter to detect and block brute-force authentication attempts.

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
R08sfcpu FirmwareOperating system
Affected:all versions
R16sfcpu FirmwareOperating system
Affected:all versions
R32sfcpu FirmwareOperating system
Affected:all versions
R120sfcpu FirmwareOperating system
Affected:all versions
R08psfcpu FirmwareOperating system
Affected:all versions
R16psfcpu FirmwareOperating system
Affected:all versions
R32psfcpu FirmwareOperating system
Affected:all versions
R120psfcpu 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
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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 CPU module model
    Access the PLC programming software (GX Works3) or check the device nameplate documentation to determine the exact CPU model number (e.g., R08sfcpu, R16sfcpu, R32sfcpu, R120sfcpu, R08psfcpu, R16psfcpu, R32psfcpu, R120psfcpu)
    Affected if The model matches any of the eight affected product names listed in the CVE
  2. Check the firmware version
    In GX Works3, navigate to the CPU module diagnostics or system information screen to view the installed firmware version
    Affected if The firmware version is any version (all versions of the affected models are vulnerable)
  3. Verify network exposure
    Check the PLC network configuration in GX Works3 under the Ethernet/CC-Link settings to determine if the Ethernet port is enabled and configured with an IP address accessible from external networks
    Affected if The device has an active Ethernet connection with a routable IP address accessible to unauthenticated network attackers
  4. Confirm remote authentication is enabled
    Check the CPU module security settings in GX Works3 under the Security -> User Authentication section to see if login authentication is configured
    Affected if User authentication is enabled, meaning the account lockout mechanism can be triggered by repeated failed login attempts
  5. Check account lockout configuration
    In the CPU module security settings, review the account lockout threshold and lockout duration policy settings
    Affected if A lockout threshold exists (even if set to a low number of attempts), confirming the vulnerable lockout mechanism is active

The environment is affected if any MELSEC iQ-R CPU module model listed (R08sfcpu, R16sfcpu, R32sfcpu, R120sfcpu, R08psfcpu, R16psfcpu, R32psfcpu, R120psfcpu) with any firmware version is accessible over the network with authentication enabled, as this allows remote attackers to trigger account lockout and cause denial of service.

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

Isolate affected devices behind firewalls or in a protected network segment to limit exposure to unauthenticated attackers; implement rate-limiting or IP-based blocking at the network perimeter to detect and block brute-force authentication attempts.

Fix this in R08sfcpu Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2021-20598 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
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