NSA and CISA Warn Hackers Are Using AI to Target Siemens PLCs in Critical Infrastructure

Five US federal agencies issued a joint cybersecurity advisory on August 19 warning that hackers are using artificial intelligence to build exploitation scripts aimed at Siemens S7 Series programmable logic controllers (PLCs) deployed across the country’s critical infrastructure.

The advisory, tracked as AA26-231A, comes from the National Security Agency (NSA), the Cybersecurity and Infrastructure Security Agency (CISA), the FBI, the Department of Energy, and the Environmental Protection Agency. “This is not a theoretical risk: it is an active threat,” the agencies wrote, adding that threat actors are conducting reconnaissance and testing exploitation techniques against real, internet-exposed Siemens hardware rather than working from a lab.

How the attacks work

According to the advisory, the threat actors are combining open source industrial automation libraries, specifically snap7.dll and python-snap7, with AI-assisted coding to build custom Python tools that mimic legitimate operational technology (OT) monitoring software. Those tools communicate over the S7comm protocol to gain read and write access to a PLC’s memory, configuration data, and ladder logic programs (the code that actually controls physical equipment).

The attackers first use internet-scanning services such as Censys and ZoomEye to locate exposed or poorly protected Siemens controllers running outdated firmware or default credentials, the agencies said. From there, they use AI to generate exploitation scripts for initial access, credential access, denial-of-service attacks, and other objectives, drawing on publicly available vulnerability information rather than any single undisclosed flaw.

“Using AI to generate exploitation scripts represents an evolution in threat actor capabilities, dramatically reducing the technical expertise and time required to develop working ICS exploitation scripts and malicious tools,” the advisory states. It adds that AI also lets attackers “rapidly leverage additional attack vectors and adapt to defensive measures.”

Targeted devices span the S7-200, S7-300, S7-400, S7-1200, and S7-1500 series, with the advisory listing specific CPU variants for each line, including the S7-1500’s F-series safety controllers. The agencies assess the activity as “persistent reconnaissance” meant to develop capabilities and pre-position for future disruptive or destructive operations, rather than an attack that has already caused confirmed damage.

An unnamed actor, but a familiar pattern

The advisory itself does not attribute the campaign to a specific government or criminal group. But as SecurityWeek noted, it arrives after separate warnings this year that Iran-linked hackers were targeting PLCs made by Siemens, Schneider Electric, and Rockwell Automation at US water utilities, including an intrusion that disrupted more than 30 community water systems in Minnesota in late July. sxz.io covered an earlier stage of that campaign, which centered on exposed Rockwell Automation MicroLogix controllers, in a prior report.

“This appears to be a continuation of the same suite of activity we suspect is affiliated with Iran targeting PLCs,” Cynthia Kaiser, senior vice president at the Halcyon Ransomware Research Center and a former FBI cyber division deputy assistant director, told The Register. “Iran-affiliated actors and adversaries are actively targeting a wide swath of operational technology because these PLCs underpin essential health, safety, and critical infrastructure across society.”

Kaiser said the new advisory’s AI details line up with what researchers had been expecting: “state-sponsored adversaries are leveraging AI across the board for discrete tasks, like code checks and scripting, to scale their operations and move faster.”

Benny Czarny, CEO and founder of critical infrastructure security firm Opswat, told the outlet the underlying problem predates AI. “I think that the bigger issue is still how exposed OT environments are,” he said. “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.”

The agencies name six sectors as most targeted: critical manufacturing, energy, water and wastewater, chemical, food and agriculture, and commercial facilities. The advisory separately warns that Siemens S7 controllers used in the Defense Industrial Base could be targeted as well, and notes that the broader PLC-targeting activity extends beyond Siemens equipment.

What the agencies are telling operators to do

The advisory’s mitigations largely mirror standard OT security guidance, applied with urgency: take an immediate inventory of every Siemens S7 controller on the network, apply firmware and TIA Portal/STEP 7 updates, verify that PLCs are not directly reachable from the internet, strengthen authentication and access controls, and deploy monitoring that can catch anomalous S7comm activity, such as connections from unexpected IP ranges, scanning on port 102, or write operations outside normal change windows.

The agencies specifically flag organizations that rely on third-party systems integrators or managed service providers with remote PLC access, warning that asset owners may not realize those relationships have left their controllers exposed to the internet in the first place.