Analyzing a Stuxnet Infection with the Sysinternals Tools, Part 1

Though I didn’t realize what I was seeing, Stuxnet first came to my attention on July 5 last summer when I received an email from a programmer that included a driver file, Mrxnet.sys, that they had identified as a rootkit. A driver that implements rootkit functionality is nothing particularly noteworthy, but what made this one extraordinary is that its version information identified it as a Microsoft driver and it had a valid digital signature issued by Realtek Semiconductor Corporation, a legitimate PC component manufacturer (while I appreciate the programmer entrusting the rootkit driver to me, the official way to submit malware to Microsoft is via the Malware Protection Center portal).

I forwarded the file to the Microsoft antimalware and security research teams and our internal review into what became the Stuxnet saga began to unfold, quickly making the driver I had received become one of the most infamous pieces of malware ever created. Over the course of the next several months, investigations revealed that Stuxnet made use of four “zero day” Windows vulnerabilities to spread and to gain administrator rights once on a computer (all of which were fixed shortly after they were revealed) and was signed with certificates stolen from Realtek and JMicron. Most interestingly, analysts discovered code that reprograms Siemens SCADA (Supervisory Control and Data Acquisition) systems used in some centrifuges, and many suspect Stuxnet was specifically designed to destroy the centrifuges used by Iran’s nuclear program to enrich Uranium, a goal the Iranian government reported the virus at least partially accomplished.

As a result, Stuxnet has been universally acknowledged as the most sophisticated piece of malware created. Because of its apparent motives and clues found in the code, some researchers believe that it’s the first known example of malware used for state-sponsored cyber warfare. Ironically, I present several examples of malware targeting infrastructure systems in my recently-published cyber-thriller Zero Day, which when I wrote the book several years ago seemed a bit of a stretch. Stuxnet has proven the examples to be much more likely than I had thought (by the way, if you’ve read Zero Day, please leave a review on Amazon.com).

Malware and the Sysinternals Tools

My last several blog posts have documented cases of the Sysinternals tools being used to help clean malware infections, but malware researchers also commonly use the tools to analyze malware. Professional malware analysis is a rigorous and tedious process that requires disassembling malware to reverse engineer its operation, but systems monitoring tools like Sysinternals Process Monitor and Process Explorer can help analysts get an overall view of malware operation. They can also provide insight into malware’s purpose and help to identity points of execution and pieces of code that require deeper inspection. As the previous blog posts hint, those findings can also serve as a guide for creating malware cleaning recipes for inclusion in antimalware products. 

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