Industrial control systems (ICS) operators have been warned that threat actors are using AI to target Siemens S7 Series programmable logic controllers (PLCs).

Attackers are deploying AI to assist with a number of malicious objectives designed to compromise operational technology (OT) systems in critical sectors like water and energy. These include to generate exploitation scripts on these PLCs for initial access post-exploitation activities.

A joint advisory by CISA, the FBI, and other relevant agencies said that critical infrastructure sectors including manufacturing, energy, water and wastewater and food and agriculture that use Siemens S7 Series and other PLC devices face significant risks from this activity.

The risks range from disruption of critical industrial processes, safety incidents, downtime to equipment damage and compromise of sensitive data – all of which could lead to significant real-world harms such as disruption to water and energy services.

As such, operators have been urged to proactively update their security measures.

Mitigations are particularly important for ICS owners and operators who work with third-party service providers or system integrators who may have remote access to PLCs, as the asset owners may not realize that their systems are exposed and at risk, the document noted.

The new publication follows earlier warnings by the US government that Iranian hackers were targeting internet-exposed industrial systems across brands like Rockwell Automation, Allen-Bradley, Schneider Electric and Siemens.

This activity is likely linked to reports in early August that water systems across multiple US states had been targeted by suspected Iranian state-backed hackers.

AI Use Marks Evolution in ICS Attacks

The latest advisory, published on August 19, noted that the use of AI to generate exploitation scripts represents an evolution in threat actor capabilities.

Threat actors have been observed using legitimate scanning services, such as Censys and ZoomEye, to identify Internet-exposed or insufficiently segmented Siemens S7 Series PLCs.

Once vulnerable systems have been identified, AI-generated scripts are deployed to find exploits. The authoring agencies noted that PLCs that are exposed to the internet are at high risk for exploitation.

After gaining access into a PLC, AI is assisting lateral movement activities and enhancing attackers’ ability to evade defenses. They have been found to leverage open-source industrial automation libraries in combination with AI-assisted scripting to create custom tools that mimic legitimate OT monitoring solutions, thereby evading detection by security teams.

These tools provide read/write access to Siemens S7 Series PLC memory, configuration data, and ladder logic programs via the S7comm protocol.

The authoring agencies believe this activity is likely designed to achieve persistent reconnaissance in critical industries for future attacks.

“For capability development, actors are testing and refining their exploitation techniques against specific PLC models to improve their ability to compromise the PLCs. To prepare for operational effects, actors are leveraging read access to understand target environments, enabling preparation and positioning for future write operations to cause disruption or other operational impacts,” the advisory read.

ICS Operators Must Engage in Proactive Defense

The US government set out a range of urgent measures ICS operators should take to mitigate the observed threat activity, including

• Proactively hunt for indicators of compromise, such as connections from non-engineering workstations, repeated connection attempts with varying parameters and connections originating from unexpected countries or IP ranges not associated with vendors or integrators
• Immediately conduct an immediate inventory of all Siemens S7 Series PLCs in your environment and apply critical patches for affected devices
• Ensure PLCs are not accessible from the internet and separate all OT and IT networks
• Strengthen access controls, including restricting PLC access to authorized engineering workstations and enabling multifactor authentication for all remote access to OT networks
• Disable web servers and unused communication protocols on Siemens S7 Series devices
• Contact Siemens for model-specific hardening recommendations

Commenting on the advisory, Benny Czarny, CEO and founder of OPSWAT, argued that the biggest takeaway is not the threat posed by AI, but the need for improved baseline security controls in ICS environments.

“AI makes it much easier for an attacker to create and modify scripts targeting PLCs, so the barrier to attacking industrial systems continues to fall. But for me the answer is not simply better AI detection. So yes, AI makes this more urgent. But the real lesson for me is still the same: stop giving attackers a path to the critical system in the first place. And do not rely on antivirus and sandboxes to protect your data flow,” he advised.