ICS Advisory (ICSA-21-033-01)

Rockwell Automation MicroLogix 1400 (Update A)

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  • CVSS v3 8.1
  • ATTENTION: Exploitable remotely
  • Vendor: Rockwell Automation
  • Equipment: MicroLogix 1400
  • Vulnerability: Buffer Overflow


This updated advisory is a follow-up to the original advisory titled ICSA-21-033-01 Rockwell Automation MicroLogix 1400 that was published February 2, 2021, to the ICS webpage on us-cert.cisa.gov.


Successful exploitation of this vulnerability may result in a denial-of-service condition.



Rockwell Automation reports the vulnerability affects the following MicroLogix 1400 controllers:

  • MicroLogix 1400, All series Version 21.6 and below



A remote unauthenticated attacker may be able to send a specially crafted Modbus packet allowing the attacker to retrieve or modify random values in the register. If successfully exploited, this may lead to a buffer overflow resulting in a denial-of-service condition. The FAULT LED will flash RED and communications may be lost. Recovery from denial-of-service condition requires the fault to be cleared by the user.

CVE-2021-22659 has been assigned to this vulnerability. A CVSS v3 base score of 8.1 has been calculated; the CVSS vector string is (AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:H).




--------- Begin Update A Part 1 of 2 ---------

Parul Sindhwad and Dr. Faruk Kazi of COE-CNDS, Veermata Jijabai Technological Institute (VJTI), India reported this vulnerability to Rockwell Automation.

--------- End Update A Part 1 of 2 ---------


Rockwell Automation recommends users with the affected controller to mitigate risk. They encourage, when possible, to combine this guidance with the general security guidelines for a comprehensive defense-in-depth strategy. Please subscribe to updates to this advisory and the Industrial Security Advisory Index to stay notified.

All users, if applicable, may disable Modbus TCP support if it is not necessary for their MicroLogix 1400 implementation. Without Modbus TCP enabled, a potential attacker does not have access to exploit the device using this vulnerability.

--------- Begin Update A Part 2 of 2 ---------

For additional information see Rockwell Automation Security Advisory PN1545.

--------- End Update A Part 2 of 2 ---------

Rockwell Automation recommends the following network-based vulnerability mitigations for embedded products:

  • Utilize proper network infrastructure controls (such as firewalls) to help ensure Modbus TCP from unauthorized sources are blocked.
  • Consult the product documentation for specific features (such as a hardware keyswitch setting), which may be used to block unauthorized changes, etc.
  • Block all traffic to EtherNet/IP or other CIP protocol-based devices from outside the manufacturing zone by blocking or restricting access to TCP and UDP Port 2222 and 44818 using proper network infrastructure controls, such as firewalls, UTM devices, or other security appliances. For more information on TCP/UDP ports used by Rockwell Automation products, see Knowledgebase Article ID 898270.

Rockwell Automation recommends the following software/PC-based mitigation strategies:

  • Run all software as a User, not as an Administrator, to minimize the impact of malicious code on the infected system.
  • Use of Microsoft AppLocker or other similar allow list application can help mitigate risk. Information on using AppLocker with Rockwell Automation products is available at Knowledgebase Article ID 546989.
  • Ensure the least-privilege user principle is followed, and user/service account access to shared resources (such as a database) is only granted with a minimum of rights as needed.

Rockwell Automation recommends the following general mitigations:

  • Use trusted software, software patches, antivirus/antimalware programs, and interact only with trusted websites and attachments.
  • Minimize network exposure for all control system devices and/or systems and ensure they are not accessible from the Internet. For further information about the risks of unprotected Internet accessible control systems, please see Knowledgebase Article ID 494865.
  • Locate control system networks and devices behind firewalls and isolate them from the business network.
  • When remote access is required, use secure methods, such as virtual private networks (VPNs), and recognize VPNs may have vulnerabilities and should be updated to the most current version available. Also recognize a VPN is only as secure as the connected devices.

CISA recommends users take defensive measures to minimize the risk of exploitation of this vulnerability. CISA reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures.

CISA also provides a section for control systems security recommended practices on the ICS webpage on us-cert.cisa.gov. Several recommended practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies.

Additional mitigation guidance and recommended practices are publicly available on the ICS webpage on us-cert.cisa.gov in the Technical Information Paper, ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation Strategies.

Organizations observing any suspected malicious activity should follow their established internal procedures and report their findings to CISA for tracking and correlation against other incidents.

No known public exploits specifically target this vulnerability. High skill level is needed to exploit.

Contact Information

For any questions related to this report, please contact the CISA at:

Email: CISAservicedesk@cisa.dhs.gov
Toll Free: 1-888-282-0870

For industrial control systems cybersecurity information:  https://us-cert.cisa.gov/ics 
or incident reporting:  https://us-cert.cisa.gov/report

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