This updated advisory is a follow-up to the original advisory titled ICSA-19-106-03 PLC Cycle Time Influences that was published April 16, 2019, on the ICS webpage on us-cert.gov.
High network load can consume CPU power in such a way that the normal operation of the device can be affected; that is, the configured cycle time can be influenced.
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Researchers have found some controllers are susceptible to a denial-of-service attack due to a flood of network packets.
ABB, Phoenix, Schneider Electric, Siemens, and WAGO are companies based in Europe that deploy their PLCs worldwide across the following critical infrastructure sectors: Chemical, Commercial Facilities, Critical Manufacturing, Dams, Energy, Food and Agriculture, Transportation Systems, and Water and Wastewater Systems.
Matthias Niedermaier (Hochschule Augsburg), Jan-Ole Malchow (Freie Universität Berlin), and Florian Fischer (Hochschule Augsburg) reported this vulnerability to CISA. Mikael Vingaard found and reported to CISA additional devices containing this vulnerability.
PLC vendors have responded to queries about this report with the following mitigations:
ABB concludes the reported behavior is not a vulnerability but is due to a misconfiguration of the PLC watchdog, which was left in the default factory settings. This has led to a configuration that does not match the expectations expressed in the test cases and the result is the PLC not reacting as intended. This misconfiguration can be fixed by setting an appropriate combination of task priority, task cycle time, and watchdog settings. Please see the “Onboard Ethernet Handling in CPU Firmware” chapter (System Technology for AC500 V2 Products > System Technology of CPU and Overall System > Onboard Technologies > Ethernet > Ethernet Protocols and Ports for AC500 V2 Products > Onboard Ethernet Handling in CPU Firmware) for further guidance.
Phoenix Contact acknowledges this as a “known, won’t fix” issue for old products. Currently available products provide countermeasures to mitigate the impact on the safety-related functionality. Phoenix Contact urges users to adhere to the Application note 107913_en_01.
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More information can be found in the VDE CERT advisory.
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Fixes are available in the Modicon M221 firmware v18.104.22.168 and the EcoStruxure Machine Expert – Basic v1.0 software (formerly SoMachine Basic) using either of the following options:
Or run the Schneider Electric Software Update tool in order to download and install EcoStruxure Machine Expert – Basic v1.0 software.
For additional information, see the Schneider Electric security notice SEVD-2019-045-01.
Schneider Electric strongly recommends following industry cybersecurity best practices, such as:
Siemens has investigated the vulnerability report on PLC cycle time influences and concludes the report does not demonstrate a valid vulnerability for Siemens PLCs.
WAGO recommends users operate the devices in closed networks or protect them with a firewall against unauthorized access. Another recommended mitigation is to limit network traffic via the switch rate limit feature according to application needs.
Please also consult the product manuals on the WAGO website, as this is a known problem for some devices. Links to product manuals and specific instructions about how to limit switch rates can be found in the VDE CERT advisory.
CISA recommends users take defensive measures to minimize the risk of exploitation of this vulnerability. Specifically, users should:
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.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.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.
For any questions related to this report, please contact the NCCIC at:
Toll Free: 1-888-282-0870
For industrial control systems cybersecurity information: http://ics-cert.us-cert.gov
or incident reporting: https://ics-cert.us-cert.gov/Report-Incident?
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