PLC Cycle Time Influences (Update A)

Risk Summary

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.

CVEs (1)

Remediations

• 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 theApplication note 107913_en_01.
• More information can be found in the VDE CERT advisory.
• Fixes are available in the Modicon M221 firmware v1.10.0.0 and the EcoStruxure Machine Expert - Basic v1.0 software (formerly SoMachine Basic) using either of the following options:Use this link to download the Machine Expert Basic software.
• 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.

Affected Vendors

Affected Products (11)