Stuxnet Heralds New Generation of Targeted Attacks

This is first in a two-part series on Stuxnet

It's the first known malware attack to target power plant and factory floor systems, but the Stuxnet worm also has opened the door to a whole new level of attack that could execute the unthinkable, manipulating and sabotaging power plants and other critical infrastructure systems.

Stuxnet has been under the microscope over the past few days as researchers around the world have picked apart and analyzed the malware's makeup and possible intent. No one knows for sure yet who is behind it -- many point to some nation-state link due to its many layers of expertise and the sophistication of the attack -- nor its specific goal, but most agree that it's a game-changer.

"We've never seen anything like this before," says Liam O Murchu, manager of operations for Symantec Security Response, which has been one of the leading teams of researchers to study the malware. "It infects those PLCs that control real, live machinery, and can have physical affects in the real world. Turning off essential parts of a plant could have drastic affects."

That could mean building up pressure in a plant system, reporting faulty data to a plant operator, or causing a complete failure of the power plant system, or some sort of catastrophe, says Eric Knapp, director of critical infrastructure markets for NitroSecurity. "People were focused on the Windows zero-days [in Stuxnet], but they were just delivery mechanisms. The concern is the payload: installing a rootkit on the control system and injecting code into PLCs. These are things that cause things to happen in the control system: so there's a potential for some pretty severe damage," he says.

Stuxnet has rocked the mostly insulated SCADA and process control world, which long had been considered relatively buffered from attack because these systems aren't Internet-connected. But with Windows systems supporting many of these plants, and the Stuxnet worm spreading via a USB stick, that was all it took to burst that bubble. "Eight months ago, there was no such thing as a virus in PLC. People thought you couldn't get to them," Knapp says. "This is proof that you indeed can infect a PLC. PLC is now an attack vector."

The Stuxnet worm first came to light over the summer and initially was considered yet another zero-day attack on Windows, exploiting the so-called "LNK" vulnerability in Windows machines via USB devices and fileshares. But upon closer inspection over the past month, it became clear that aside from its target of SCADA systems, this was no ordinary Windows attack. It exploits four different Windows zero-day vulnerabilities, including a print spooler bug and two others that escalate user privileges to first infect a Windows machine running Siemens software to manage control systems. It then looks for a Siemens S7 PLC, which it attacks and changes its programming by injecting code into it.

Symantec's Murchu says the worm has one rootkit that hides files on a UB key on the Windows machine to avoid discovery, and another rootkit that hides the code it sends to the PLCs. "It doesn't want the PLC to see those changes, because then it would realize something was wrong," Murchu says.

Stuxnet injects a piece of code into a Siemens control system -- past the SCADA and engineering software, and into the "ladder logic," says Gary McGraw, CTO at Cigital. "It's not just malicious code rooting SCADA boxes," he says. "It's after the control system and tries to inject some code into the logic controls of a physical process."

The worry now is that Stuxnet will be reinvented or reused in some form for other attacks. The concern is that future such attacks will be less likely to be discovered. "This malware takes some serious resources to get it accomplished, including covert operations and intell. But the real problem now that it's been discovered and researchers are taking it apart, the techniques it uses are available for everyone," McGraw says.

Stuxnet has even put the much-publicized and analyzed Aurora targeted attacks into perspective: the attacks on Google, Adobe, Intel and other major companies exposed earlier this year were spread via a relatively unsophisticated attack that went after an old browser, Internet Explorer 6. Although they indeed were successful in stealing some intellectual property, the attacks were nowhere near as complex as Stuxnet, experts say.

In an odd twist for an attack so laser-focused, the Stuxnet worm spread wide beyond its intended mark and into the wild, infecting Windows machines worldwide, nearly 60 percent of which were in Iran, according to Symantec's data.

Next Page: Attackers likely didn't intend for Stuxnet to spread "It caught the public's attention very quickly -- there were thousands of infections at the height of it," NitroSecurity's Knapp says. "If an attack was delivered more strategically, then it wouldn't draw that type of attention to itself" and be harder to detect, he says.

Symantec's Murchu, like other researchers, says just why Stuxnet spread beyond its targeted Siemens PLC system remains a mystery. "From looking at the code and the way it was written, and the techniques used in it, they didn't want this to spread ... It was to stay local to the company it was trying to infect," he says. "Somehow it did spread. It looks like they wanted to keep it low-key, and maybe it spread" somehow, he says.

Michael Sconzo, principal security consultant with NetWitness, concurs that the attackers letting the worm escape into the wild just doesn't add up. "Why invest all of that time and money buying zero-days and let it get out into the wild," Sconzo says. "If that and you steal a digital certificate, I would think that they would have been careful the worm didn't get out of hand."

Even so, the attack raises the bar for what has been seen thus far in targeted attacks. "Yesterday the world learned that all the stuff covered so far about zero-days, a rootkit, and a botnet wasn't what the [attackers] were trying to do. What they were doing was getting into the actual control software at the deepest level," Cigital's McGraw says.

A German researcher says the attack was likely aimed at an Iranian nuclear power plant. Ralph Langner said in a blog posting that the attack is "sabotage" and required much insider knowledge in order to pull off. "The best way to approach Stuxnet is not to think of it as a piece of malware like Sasser or Zotob, but to think of it as part of an operation -- operation myrtus. Operation myrtus can be broken down into three major stages: Preparation, infiltration, and execution," he wrote.

Researchers agree this was a highly coordinated attack that required various types of skill. "You needed people skilled in different areas to make this work: a person who writes code that affects PLCs is different from a person who infects USB drives. The skills needed to write this code is very different" for each, says Murchu.

It was likely a large project team, with a project manager, some quality assurance, and testing elements as well, he says. "They had to identify what type of hardware, PLCs, and then after that was established, creating the project to fit the target they were trying to attack. You get people who know SCADA and can test on PLCs," he says. "This was either an industrial funded group with deep pockets, or nation-state sponsored. But I am only speculating here."

Meanwhile, while the specific payload of Stuxnet is only aimed at the Siemens S7, the malware model is likely to be reused in some way and emulated in future targeted attacks, experts say. "We'll see more of these types of things in the future," says Marc Maiffret, chief technology officer at eEye Digital Security.

Next: What this means for the security of power plant and industrial control systems

Have a comment on this story? Please click "Discuss" below. If you'd like to contact Dark Reading's editors directly, send us a message.