CVE-2018-7791
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 · uneditedA Permissions, Privileges, and Access Control vulnerability exists in Schneider Electric's Modicon M221 product (all references, all versions prior to firmware V1.6.2.0). The vulnerability allows unauthorized users to overwrite the original password with their password. If an attacker exploits this vulnerability and overwrite the password, the attacker can upload the original program from the PLC.
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 confidenceThis is an authentication/authorization bypass vulnerability in Schneider Electric Modicon M221 PLCs. An unauthenticated attacker can overwrite the device's password, then use that new password to upload the original program from the PLC. This represents a complete compromise of confidentiality and partial compromise of integrity.
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< 1.6.2.0CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Confirm Modicon M221 PLC presenceIdentify all PLCs on the network and verify the device model is Schneider Electric Modicon M221. This can be done through network scanning tools or by accessing the device via Schneider Electric's SoMachine Basic or EcoStruxure Machine Expert software and checking the controller properties.Affected if The device is a Modicon M221 PLC
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Check firmware versionUsing SoMachine Basic or EcoStruxure Machine Expert, connect to the PLC and retrieve the firmware version from the controller properties or device information. Compare the installed version against the affected range of < 1.6.2.0.Affected if The firmware version is less than 1.6.2.0
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Assess network exposureDetermine if the Modicon M221 PLC is directly accessible from untrusted networks or the internet. Check firewall rules, network segmentation, and ACLs governing access to the PLC's IP address on relevant ports (typically ports used by Modbus/TCP or engineering protocol access).Affected if The PLC is accessible from untrusted or unmanaged network segments without proper filtering
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Review for unauthorized access or password changesAudit device logs if available through the engineering software or any connected management interface for signs of unexpected password modifications, unauthorized program read/upload operations, or authentication anomalies.Affected if Evidence exists of unauthorized password changes or program read operations performed by an unknown source
A user is affected if they have a Modicon M221 PLC running firmware version below 1.6.2.0 that is network-accessible to potential attackers, as this allows unauthenticated password overwrite and program extraction.
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.
dbcve · scoped1.6.2.0
Update Modicon M221 firmware to V1.6.2.0 or later. Until patched, isolate affected devices on a restricted network segment and monitor for unauthorized access attempts.
Modicon M221 Firmware V1.6.2.0 or later
- Download Modicon M221 firmware version 1.6.2.0 or later from the official Schneider Electric website
- Verify the firmware integrity using checksums provided by Schneider Electric
- Schedule planned downtime for the PLC
- Connect to the Modicon M221 PLC using appropriate tooling (e.g., SoMachine Basic or EcoStruxure Machine Expert)
- Follow Schneider Electric's official firmware update procedure to upload the new firmware to the PLC
- After upgrade, verify the firmware version is 1.6.2.0 or later
- Change the PLC password to a new strong password after the upgrade to ensure security
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2018-7791 — 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-2018-7791 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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