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SCADA security is better and worse than we think

'Kill chains' are long and attack-stopping weak links are many

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AUSCERT 2013 First the good news: for all the known vulnerabilities that exist in the SCADA world, exploiting them in a way that can actually “shut down a power plant” is harder than most people (particularly including media) realise.

That's the reassuring view put forward by Mark Fabro of Lofty Perch, in his spot at this year's AusCERT 2013.

That's because even though in a fairly short time the number of known vulnerabilities in programmable logic controllers (PLCs) has gone from zero to 171, turning the existence of a vulnerability into a successful exploit is a much more complex task than merely launching an attack against the individual device.

The industry, he said, is “stuck in a bit of a funk” thinking that one vulnerability will bring down whole systems – chiefly because we forget that one of the main points of SCADA systems is to present information to an operator.

If an operator notices unusual processes taking place on a system that aren't in his operational manual, Fabro said, it's expected that the employee will take some sort of action, or at least investigate what's going on. So the gap between finding a system vulnerability and causing a nationwide blackout is quite wide.

However, Fabro said, as attackers become more sophisticated and learn more about both the SCADA systems and their control environments, the likelihood of more dangerous SCADA-based attacks increases.

A key part of defending against those attacks that may occur, he said, is to start with a thorough understanding of the “kill chain” – the number of steps and scenarios an attacker is forced to step through to achieve what they want.

Breaking into a system, finding its control system, presenting false information to an operator, and then exploiting the attack doesn't sound too difficult. However, to attack the bulk power system, Fabro said “the attack tree we've built contains 143,000 scenarios the attacker would need to get by”, and if any one of those fails, “he can't get in”.

And if you're spotting a pattern emerging, you're right: the operator isn't just an important point of defence, but also the biggest weakness.

“Time and time again people are the vector, the kill-chain's tipping point is at people,” he said. “An individual who was tricked and had done something inappropriate – clicked on the link in the e-mail, let someone into the facility.”

It points to a difficult cultural problem in defending industrial control systems, because in trying to instil a new security culture, “the people you're risking upsetting are the ones you're relying on to run the system.” ®

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