Cybersecurity researchers have elaborated a novel attack technique that weaponizes programmable logic controllers (PLCs) to gain an initial foothold in engineering workstations and subsequently invade the operational technology (OT) networks.
Dubbed "Evil PLC" attack by industrial security firm Claroty, the issue impacts engineering workstation software from Rockwell Automation, Schneider Electric, GE, B&R, Xinje, OVARRO, and Emerson.
Programmable logic controllers are a crucial component of industrial devices that control manufacturing processes in critical infrastructure sectors. PLCs, besides orchestrating the automation tasks, are also configured to start and stop processes and generate alarms.
It's hence not surprising that the entrenched access provided by PLCs have made the machines a focus of sophisticated attacks for more than a decade, starting from Stuxnet to PIPEDREAM (aka INCONTROLLER), with the goal of causing physical disruptions.
"These workstation applications are often a bridge between operational technology networks and corporate networks," Claroty said. "An attacker who is able to compromise and exploit vulnerabilities in an engineering workstation could easily move onto the internal network, move laterally between systems, and gain further access to other PLCs and sensitive systems."
With the Evil PLC attack, the controller acts as a means to an end, permitting the threat actor to breach a workstation, access to all the other PLCs on the network, and even tamper with the controller logic.
Put differently, the idea is to "use the PLC as a pivot point to attack the engineers who program and diagnose it and gain deeper access to the OT network," the researchers said.
The whole sequence plays out as follows: An opportunistic adversary deliberately induces a malfunction on an internet-exposed PLC, an action that prompts an unsuspecting engineer to connect to the infected PLC using the engineering workstation software as a troubleshooting tool.
In the next phase, the bad actor leverages the previously undiscovered flaws identified in the platforms to execute malicious code on the workstation when an upload operation is performed by the engineer to retrieve a working copy of the existing PLC logic.
"The fact that the PLC stores additional types of data that are used by the engineering software and not the PLC itself" creates a scenario wherein the unused data stored on the PLC can be modified to manipulate the engineering software, the researchers pointed out.
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"In most cases, the vulnerabilities exist because the software fully trusted data coming from the PLC without performing extensive security checks."
In an alternative theoretical attack scenario, the Evil PLC method can also be used as honeypots to lure threat actors into connecting to a decoy PLC, leading to a compromise of the attacker's machine.
Claroty further called out the absence of security protections in the public-facing industrial control system (ICS) devices, thereby making it easier for threat actors to alter their logic via rogue download procedures.
To mitigate such attacks, it's recommended to limit physical and network access to PLCs to authorized engineers and operators, enforce authentication mechanisms to validate the engineering station, monitor OT network traffic for anomalous activity, and apply patches in a timely fashion.