As Iran met in Kazakhstan this week with members of the UN Security Council to discuss its nuclear program, researchers announced that a new variant of the sophisticated cyberweapon known as Stuxnet had been found, which predates other known versions of the malicious code that were reportedly unleashed by the U.S. and Israel several years ago in an attempt to sabotage Iran’s nuclear program.
The new variant was designed for a different kind of attack against centrifuges used in Iran’s uranium enrichment program than later versions that were released, according to Symantec, the U.S-based computer security firm that reverse-engineered Stuxnet in 2010 and also found the latest variant.
The new variant appears to have been released in 2007, two years earlier than other variants of the code were released, indicating that Stuxnet was active much earlier than previously known. A command-and-control server used with the malware was registered even earlier than this, on Nov. 3, 2005.
Like three later versions of Stuxnet that were released in the wild in 2009 and 2010, this one was designed to attack Siemens PLCs used in Iran’s uranium enrichment program in Natanz.
But instead of changing the speed of spinning centrifuges controlled by the PLCs, as those later versions did, this one focused on sabotaging the operation of valves controlling the flow of uranium hexaflouride gas into the centrifuges and cascades — the structure that connects multiple centrifuges together so that the gas can pass between them during the enrichment process. The malware’s goal was to manipulate the movement of gas in such a way that pressure inside the centrifuges and cascade increased five times the normal operating pressure.
“That would have very dire consequences in a facility,” says Liam O’Murchu, manager of security response operations for Symantec. “Because if pressure goes up, there’s a good chance the gas will turn into a solid state, and that will cause all sorts of damage and imbalances to the centrifuges.”
The new finding, described in a paper released by Symantec on Tuesday (.pdf), resolves a number of longstanding mysteries around a part of the attack code that appeared in the 2009 and 2010 variants of Stuxnet but was incomplete in those variants and had been disabled by the attackers.
The 2009 and 2010 versions of Stuxnet contained two attack sequences that each targeted different models of PLCs made by Siemens being used in Iran’s uranium enrichment plant — the Siemens S7-315 and S7-417 models of PLC.
In these later variants of Stuxnet, however, only the 315 attack code worked. The 417 attack code had been deliberately disabled by the attackers and was also missing important blocks of code that prevented researchers from determining definitively what it was designed to do. As a result, researchers have long guessed that it was used to sabotage valves, but couldn’t say for certain how it affected them. There were also mysteries around why the attack code was disabled — was it disabled because the attackers had failed to finish the code or had they disabled it for some other reason?
The 2007 variant resolves that mystery by making it clear that the 417 attack code had at one time been fully complete and enabled before the attackers disabled it in later versions of the weapon. And because the 2007 variant only contained the 417 attack code — with no code attacking the Siemens 315 PLC — it appears that the attackers disabled the 417 code in later versions because they wanted to change their tactics, dropping their focus on sabotaging the valves in order to focus instead on sabotaging the spinning centrifuges.
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Stuxnet Missing Link Found, Resolves Some Mysteries Around the Cyberweapon
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