Ralph Langer has written the definitive analysis of Stuxnet: short, popular version, and long, technical version.

Stuxnet is not really one weapon, but two. The vast majority of the attention has been paid to Stuxnet’s smaller and simpler attack routine — the one that changes the speeds of the rotors in a centrifuge, which is used to enrich uranium. But the second and “forgotten” routine is about an order of magnitude more complex and stealthy. It qualifies as a nightmare for those who understand industrial control system security. And strangely, this more sophisticated attack came first. The simpler, more familiar routine followed only years later — and was discovered in comparatively short order.


Stuxnet also provided a useful blueprint to future attackers by highlighting the royal road to infiltration of hard targets. Rather than trying to infiltrate directly by crawling through 15 firewalls, three data diodes, and an intrusion detection system, the attackers acted indirectly by infecting soft targets with legitimate access to ground zero: contractors. However seriously these contractors took their cybersecurity, it certainly was not on par with the protections at the Natanz fuel-enrichment facility. Getting the malware on the contractors’ mobile devices and USB sticks proved good enough, as sooner or later they physically carried those on-site and connected them to Natanz’s most critical systems, unchallenged by any guards.

Any follow-up attacker will explore this infiltration method when thinking about hitting hard targets. The sober reality is that at a global scale, pretty much every single industrial or military facility that uses industrial control systems at some scale is dependent on its network of contractors, many of which are very good at narrowly defined engineering tasks, but lousy at cybersecurity. While experts in industrial control system security had discussed the insider threat for many years, insiders who unwittingly helped deploy a cyberweapon had been completely off the radar. Until Stuxnet.
And while Stuxnet was clearly the work of a nation-state — requiring vast resources and considerable intelligence — future attacks on industrial control and other so-called “cyber-physical” systems may not be. Stuxnet was particularly costly because of the attackers’ self-imposed constraints. Damage was to be disguised as reliability problems. I estimate that well over 50 percent of Stuxnet’s development cost went into efforts to hide the attack, with the bulk of that cost dedicated to the overpressure attack which represents the ultimate in disguise — at the cost of having to build a fully-functional mockup IR-1 centrifuge cascade operating with real uranium hexafluoride. Stuxnet-inspired attackers will not necessarily place the same emphasis on disguise; they may want victims to know that they are under cyberattack and perhaps even want to publicly claim credit for it.
Related: earlier this month, Eugene Kaspersky said that Stuxnet also damaged a Russian nuclear power station and the International Space Station.

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