CVE-2022-40267
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 · uneditedPredictable Seed in Pseudo-Random Number Generator (PRNG) vulnerability in Mitsubishi Electric Corporation MELSEC iQ-F Series FX5U-xMy/z (x=32,64,80, y=T,R, z=ES,DS,ESS,DSS) with serial number 17X**** or later, and versions 1.280 and prior, Mitsubishi Electric Corporation MELSEC iQ-F Series FX5U-xMy/z (x=32,64,80, y=T,R, z=ES,DS,ESS,DSS) with serial number 179**** and prior, and versions 1.074 and prior, Mitsubishi Electric Corporation MELSEC iQ-F Series FX5UC-xMy/z (x=32,64,96, y=T, z=D,DSS)) with serial number 17X**** or later, and versions 1.280 and prior, Mitsubishi Electric Corporation MELSEC iQ-F Series FX5UC-xMy/z (x=32,64,96, y=T, z=D,DSS)) with serial number 179**** and prior, and versions 1.074 and prior, Mitsubishi Electric Corporation MELSEC iQ-F Series FX5UC-32MT/DS-TS versions 1.280 and prior, Mitsubishi Electric Corporation MELSEC iQ-F Series FX5UC-32MT/DSS-TS versions 1.280 and prior, Mitsubishi Electric Corporation MELSEC iQ-F Series FX5UJ-xMy/z (x=24,40,60, y=T,R, z=ES,ESS) versions 1.042 and prior, Mitsubishi Electric Corporation MELSEC iQ-F Series FX5UJ-xMy/ES-A (x=24,40,60, y=T,R) versions 1.043 and prior, Mitsubishi Electric Corporation MELSEC iQ-F Series FX5S-xMy/z (x=30,40,60,80, y=T,R, z=ES,ESS) versions 1.003 and prior, Mitsubishi Electric Corporation MELSEC iQ-F Series FX5UC-32MR/DS-TS versions 1.280 and prior, Mitsubishi Electric Corporation MELSEC iQ-R Series R00/01/02CPU versions 33 and prior, Mitsubishi Electric Corporation MELSEC iQ-R Series R04/08/16/32/120(EN)CPU versions 66 and prior allows a remote unauthenticated attacker to access the Web server function by guessing the random numbers used for authentication from several used random numbers.
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 confidenceThe Web server function in Mitsubishi MELSEC iQ-F and iQ-R Series PLCs uses a weak PRNG with predictable seeds for session authentication tokens. An attacker can collect several used random numbers and predict future authentication tokens, enabling remote unauthenticated access to the web server function.
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 dataall versionsall versionsall versionsall versionsall versionsall versionsall versionsall versionsCVSS 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
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
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 checksWork through these to decide whether this CVE applies to you.
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Identify the PLC modelCheck the physical label or use GX Works3 software to confirm the device is an FX5u or FX5uc series model (e.g., FX5u-80MT/ESS, FX5uc-32MT/D)Affected if The model matches any of: FX5u-80MT/ESS, FX5u-32MT/DSS, FX5u-64MT/DSS, FX5u-80MT/DSS, FX5uc-32MT/D, FX5uc-64MT/D, FX5uc-96MT/D, or FX5uc-32MT/DSS
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Confirm web server function is enabledIn GX Works3, navigate to Parameter > CPU Parameter > Web Server Setting, or access the PLC web interface on port 80/443 if externally exposedAffected if Web server function is enabled or accessible on the network
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Verify firmware versionIn GX Works3, go to CPU Module > Product Information, or access the web server login page and check the firmware/version info displayedAffected if Any firmware version is present (all versions of affected models are vulnerable)
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Assess network exposureReview network firewall rules, VLAN configurations, and port access lists to determine if the PLC web server (ports 80/443) is reachable from untrusted networksAffected if The web server is reachable from the corporate network, internet, or any untrusted segment
If the device is an affected FX5u or FX5uc model and the web server function is enabled and network-accessible, the environment is vulnerable to predictable session token attacks.
Generated from the published advisory. Verify against your own configuration.
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 dataUpdate firmware to patched versions (FX5 series: 1.281+ or 1.075+, iQ-R: R00/01/02CPU v34+, R04/08/16/32/120(EN)CPU v67+). If updates are not immediately feasible, disable or restrict network access to the web server function.
- Consultation6.0 h
- Implementation12.0 h
- Testing6.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2022-40267 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2022-40267 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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
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