Sophisticated Stuxnet Worm Uses 4 Microsoft Zero-Day Bugs

Security researchers revealed today the Stuxnet worm has been exploiting four zero-day vulnerabilities in Windows in an attempt to infect industrial control systems.

In the months since Stuxnet was first publicized in July, much of the attention focused on a now-patched Microsoft Windows bug tied to the way shortcut files are parsed on vulnerable machines. Researchers reported today however that the malware has actually been seen exploiting multiple zero-day bugs, including two that Microsoft said remain unpatched.

"If I have to single something out [as the most interesting]—which is hard in this case—then I'd go for the fact that Stuxnet exploits four previously unknown vulnerabilities," said Roel Schouwenberg, senior antivirus researcher at Kaspersky Lab. "But overall, the thought which has been put into Stuxnet is just amazing. Four zero-days, two stolen [digital] certificates, knowing SCADA systems inside and out—it's all been very carefully orchestrated."

In addition to the Windows shortcut bug, the worm also used a vulnerability in Windows' Print Spooler service that was patched today by Microsoft. Still left open, however, are two privilege escalation vulnerabilities the malware tries to use to gain control of infected systems.

"One of these EoP [escalation of privilege] vulnerabilities affects Windows XP and the other affects Windows Vista, Windows 7, Windows Server 2008 and Windows Server 2008 R2," blogged Jerry Bryant, group manager of Response Communications at Microsoft. "These are local EoP issues, which means that an attacker, in this case Stuxnet, already has permission to run code on the system or has compromised the system through some other means.

"We are currently working to address both issues in a future bulletin," Bryant added.

First reported by security vendor VirusBlokAda, the worm targeted Siemens' Simatic WinCC and PCS 7 software, which run on industrial control systems.

In the months since the worm became publicly known, the number of infected machines in India has continued to grow, Schouwenberg said. The amount of infected machines in Iran and Indonesia is significantly lower than earlier in the year, he added.

According to Siemens spokesperson Michael Krampe, Siemens has identified 15 customers that found Stuxnet on their systems, and "each was able to detect and remove the virus without any impact to their operations."

"Luckily, most control system operators separate their control network from their business and public networks," noted Mike Sconzo, senior security analyst at NetWitness. "That has been a limiting factor in keeping the number of viable infections down.  Even though the initial infection vector was discovered to be based on USB drives, newer information points to Stuxnet being able to replicate via the network. Because of the limited network connectivity and the restrictions imposed on employees to not plug USB drives into controls systems, this threat has not been as serious as it could have been.

"While being regarded as the first targeted attack against industrial systems in the wild, it will likely not be the last," he added. "Being a first effort in the target space and only going after a limited number of system types, it has accomplished an amazing amount."