CVE-2021-33012Public exploitNetwork attack vector

Unauthenticated PLC fault via improperly validated commands

Published Jul 9, 2021 · Updated Jun 3, 2026

Improper input validation in Rockwell Automation MicroLogix 1100, all versions, allows remote attackers to fault the PLC with crafted commands. The controller's command-processing path fails to validate crafted network commands, causing a fault whenever the controller is switched to RUN mode. No authentication is required, and every subsequent switch to RUN mode faults the controller again, preventing normal control execution.

CVSS severity8.6
High
EPSS probability2.64%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Rockwell Automation MicroLogix 1100, all versions, allows remote attackers to fault the PLC with crafted commands. The controller's command-processing path fails to validate crafted network commands, causing a fault whenever the controller is switched to RUN mode. No authentication is required, and every subsequent switch to RUN mode faults the controller again, preventing normal control execution.

The record

CVE
CVE-2021-33012
Published
Jul 9, 2021
Updated
Jun 3, 2026
Vendor
Rockwell Automation
Product
MicroLogix 1100
Classifications
CWE-20, T0814
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 9, 2021CVE publishedPublication date reported by the CVE source.
  2. Jun 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=All Versions

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Rockwell Automation · MicroLogix 1100version=All Versions

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
8.6NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
T0814Denial of Service

Public exploit references

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Technologies

Your stack

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Your stack

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