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There are mitigations available for an uncontrolled resource consumption vulnerability in programmable logic controllers (PLCs) for ABB, Phoenix Contact, Schneider Electric, Siemens, and WAGO, according to a report with NCCIC.

High network load can consume CPU power in such a way the normal operation of the device can be affected to the point where the configured cycle time can be influenced.

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Public exploits are available for the remotely exploitable vulnerability. An attacker with low skill level could leverage the vulnerability.

Matthias Niedermaier (Hochschule Augsburg), Jan-Ole Malchow (Freie Universität Berlin), and Florian Fischer (Hochschule Augsburg) discovered the vulnerability.

Cyber Security

The following PLCs are suffer from the issue:
• ABB 1SAP120600R0071 PM554-TP-ETH
• Phoenix Contact 2700974 ILC 151 ETH
• Schneider Electric’s Modicon M221
• Siemens 6ES7211-1AE40-0XB0 Simatic S7-1211
• Siemens 6ES7314-6EH04-0AB0 Simatic S7-314
• Siemens 6ED1052-1CC01-0BA8 Logo! 8
• WAGO 750-889 Controller KNX IP
• WAGO 750-8100 Controller PFC100
• WAGO 750-880 Controller ETH
• WAGO 750-831 Controller BACnet/IP

In the vulnerability, researchers found some controllers are susceptible to a denial-of-service attack due to a flood of network packets.

CVE-2019-10953 is the case number assigned to this vulnerability which has a CVSS v3 base score of 7.5.

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.

PLC vendors report 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. 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.

Fixes are available in Schneider’s 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:

1. Download option one

2. Or run the Schneider Electric Software Update tool in order to download and install EcoStruxure Machine Expert – Basic v1.0 software.

Click here to view Schneider Electric’s security notice SEVD-2019-045-01.

Schneider Electric recommends following industry cybersecurity best practices:
• Physical controls should be in place so no unauthorized person would have access to the ICS and safety controllers, peripheral equipment, or the ICS and safety networks
• All controllers should reside in locked cabinets and never be left in the “Program” mode
• All programming software should be kept in locked cabinets and should never be connected to any network other than the network for the devices it is intended
• All methods of mobile data exchange with the isolated network (e.g., CDs, USB drives, etc.) should be scanned before use in terminals or any node connected to these networks
• Laptops that have connected to any other network besides the intended network should never be allowed to connect to the safety or control networks without proper sanitation

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.

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.

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