AusCERT 2012: Security and standards, not “air gaps”, needed to protect SCADA systems

SCADA system managers need to learn to better understand the world of cybersecurity, rather than rely on a misplaced faith in “air gaps” for protection, says Eric Byres, VP and CTO of engineering of Tofino Security.

“The whole concept of trying to protect SCADA systems with air gaps is a myth,” the SCADA expert Byres told AusCERT delegates.

People implementing air gaps do so in the belief that “the bad things will never happen to the control systems” – but there are too many vectors that attacks like Stuxnet are able to use to get around a lack of a network connection.

“I have occasionally seen air gaps … some of the core control systems in the nuclear industry might have real air gaps,” he said. However, it’s very uncommon because the control system practically demands a network connection because of SCADA’s “hunger for information” (and its need for code updates). And, of course, there’s remote access, required by any SCADA system.

Control system networks, Byres said, should instead be based on the same practices that we consider valuable in corporate networks, such as subdividing networks. Segmenting business networks to implement line-of-business security policies is also a good idea in industrial control.

“I think if you focus on USB keys, or focus on the network, we’re making a huge mistake,” Byres said. If attempts to air gap a SCADA system were too successful, the outcome would be to force traffic (software updates, or control recipes) onto the “sneakernet” – which is probably even worse-protected than a known and managed network connection.

There is a also good opportunity in the SCADA world to learn from the mistakes of the IT industry, he said.

“There have been a lot of silver bullets and red herrings in the IT industry. Deep packet inspection and intrusion detection systems apply very well to control systems, especially what Byres described as the “last line of defence” environments, because “the deeper you go into the system”, the more steady-state it becomes. And that means “any change you see in the IDS logs, you already know is bad.”

The ANSI/ISA-99 standards, formalising the conceptual model of segmentation, are far better than the air gap since they define the points at which traffic (and security) can be managed.

It’s also vital to keep people in mind, Byres said. The engineer in charge of industrial control systems has a professional mandate that he must “keep the lights on”.

“That guy’s not going to say, ‘the security policy says I should let the lights go out’,” he said, “he’ll break the security policy if he has to. He has to keep the sewage flowing – and it has to flow through the pipes, not through the parks.”

Byres also emphasised the need for industrial control systems to be protected by technologies that understand the traffic specific to SCADA – “you need deep packet inspection to read the data the controllers are sending to each other”.


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