S4x14 CONFERENCE -- Miami -- A researcher has rigged a programmable logic controller (PLC) with a low-cost hacking tool that can shut down a process control network with a text message.

The so-called PLCpwn prototype took Digital Bond researcher Stephen Hilt less than two weeks and about $400 to build; it uses existing Metasploit attack modules that previously had been created by his firm. Hilt, who gave details on the tool here today, said he got the inspiration for the tool from a DARPA-sponsored hacking tool built on a power strip, called Power Pwn. "It was for remote access to the network via a device that has a likeness to ordinary power [equipment]," he said. "We were always joking around and said, 'What if this was a PLC?'"

PLCpwn was a natural progression in a post-Stuxnet world. "You know how it goes once you learn from Stuxnet," says Ralph Langner, founder of Langner Communications. "But what you really want to do to infiltrate is to compromise contractors" or the supply chain, Langner said.

Idaho National Laboratory, meanwhile, has been working on algorithms and coding tricks to miniaturize attack code so it can hide on a small embedded CPU. Jason Larsen, an INL security researcher, spoke here yesterday about that research.

"Larsen [has] basically the same approach and idea: a small device you can embed somewhere and talk to that device using radio signals. They were thinking in the same direction," Langner said.

Dale Peterson, CEO of Digital Bond, said he had challenged Hilt to come up with a small-slot attack module and to use text messaging to set off a simulated attack, using modules like the "CPU STOP" Metasploit module his team had previously written as part of its Project Basecamp vulnerability research.

"When you talk about nation-states not wanting to go mess around with relying on going through security perimeters," then ICS/SCADA operators need to test for these weaknesses, Peterson said.

Hilt was able to use Digital Bond's in-house Allen-Bradley ControLogix PLC for the experiment. After a little trial and error with the tool platform, he ended up using 5-volt Raspberry Pi board. For communication to the device, he used a DualComm Tap, plus a DroneCell card for drone projects that basically serves as a cell phone for text and phone communications. He also wrote some Ruby scripts to allow PLCpwn to receive text messages. In its first iteration, PLCpwn can shut down an industrial subnet with a text message.

"It can cause a large disruption with a single text message," Hilt said. "It will sweep an entire subnet with STOP CPU," and is capable of data exfiltration and injection-style attacks, he says.

The attack tool basically lets an attacker bypass perimeter security and air gaps as well, he says. "If I could do it, how much could a motivated attacker do? A well-funded one would miniaturize the hardware, customize the firmware, and pay more attention to the physical appearance and [write] more exploits," he said.

[A security researcher has discovered a pair of zero-day vulnerabilities in a popular family of Siemens industrial control system switches that could allow an attacker to take over the network devices without a password. See Zero-Day Flaws Found, Patched In Siemens Switches.]

Hilt said he's planning to rewrite the code for faster performance, as well as create more scripts for different attack vectors. He's also working with a friend on standing up a 3G cell tower for out-of-band communications, he says.

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