CVE-2021-33012
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 · uneditedRockwell Automation MicroLogix 1100, all versions, allows a remote, unauthenticated attacker sending specially crafted commands to cause the PLC to fault when the controller is switched to RUN mode, which results in a denial-of-service condition. If successfully exploited, this vulnerability will cause the controller to fault whenever the controller is switched to RUN mode.
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 confidenceRockwell Automation MicroLogix 1100 PLCs contain a denial-of-service vulnerability where remote, unauthenticated attackers can send specially crafted commands causing the controller to fault when switched to RUN mode, rendering the PLC inoperable until remediated.
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 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
- Changed
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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 checksWork through these to decide whether this CVE applies to you.
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Identify the PLC modelAccess the PLC controller or its management interface and verify the hardware model number is MicroLogix 1100. This can be done via RSLogix/MicroStudio by connecting to the controller and viewing the controller properties, or by physically inspecting the controller nameplate.Affected if The device is a Rockwell Automation MicroLogix 1100 PLC
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Confirm firmware versionIn RSLogix/MicroStudio, connect to the controller and navigate to the controller properties or system information to retrieve the firmware revision. Alternatively, access the embedded web server if enabled and check the firmware version listed on the Device Status page.Affected if Any firmware version is installed on the MicroLogix 1100 (all versions are affected)
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Assess network exposureReview network architecture and determine if the MicroLogix 1100 is directly accessible from untrusted networks such as the internet or demilitarized zones. Check router/firewall configurations to identify any exposed IP addresses or routes reaching the PLC's EtherNet/IP port (typically port 44818).Affected if The PLC has direct IP connectivity from untrusted or external networks without network segmentation or firewall protection
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Verify port accessibilityPerform a port scan from an external or untrusted network segment toward the PLC's IP address to confirm whether EtherNet/IP ports (44818/TCP, 2222/TCP) or other management ports are open and reachable from outside the trusted network.Affected if Communication ports are open and reachable from untrusted network segments
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Check firewall rulesInspect the firewall or network device protecting the PLC to verify if explicit deny rules or access control lists block unauthorized external access to the PLC's IP address and ports.Affected if No firewall rules exist to restrict access to the PLC from untrusted sources, or rules are misconfigured to allow unrestricted access
If the MicroLogix 1100 PLC is network-accessible from untrusted/external networks without proper firewall segmentation, the environment is vulnerable to this denial-of-service attack.
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 dataImplement network segmentation and firewall rules to restrict unauthorized external access to the PLC; contact Rockwell Automation for firmware updates as this affects all versions.
- Consultation8.0 h
- Implementation16.0 h
- Testing12.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $11,200.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-33012 — 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-2021-33012 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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