Researchers exploit worm's weakness and build network scanner technology that finds and cleans up victims' machines

Researchers spent the weekend building a proof-of-concept set of tools to kill the Conficker worm after discovering something telling about the malware: It changes the way Windows machines appear on the network.

The work of HoneyNet Project researchers Felix Leder and Tillmann Werner, along with Dan Kaminsky, director of penetration testing for IOActive, led to today's release of an open-source Conficker network-scanning tool, as well as several commercial-grade scanning tools that automatically detect Conficker-infected machines -- including a plug-in to Tenable Security's Nessus tool, a software-as-a-service tool from Qualys, as well as tools from McAfee/Foundstone, Nmap, and nCircle. These vendors and organizations, all members of the Conficker Working Group, built their tools around the researchers' PoC.

The researchers found that you can basically "ask" a machine if it's infected by Conficker, and it will tell you. "Conficker-infected machines respond differently to a specific request than clean ones. The response contains a distinctive error code," Leder and Werner said in an email interview.

This network "view" of the exploit is relatively unique. "You can sweep the entire network, even the portions you don't have administrative control over, during lunch," says IOActive's Kaminsky, who helped the vendors integrate Leder and Warner's PoC into their enterprise-friendly products. "Network scanning as an exploit-detection mechanism is very rare and quite appreciated here."

The new Conficker tools are timely: PCs infected with the third version of the worm, Conficker.C, are scheduled to "phone home" and receive their updates on April Fool's Day. Although security researchers aren't expecting major problems that day, the tools can catch any infections of any Conficker worm version. (To read about some hands-on experience with the new tools, check out this Evil Bytes blog post).

Joe Stewart, senior malware researcher for SecureWorks, says the Conficker.C domains are being closely monitored by researchers. And Conficker can already get updates via its peer-to-peer architecture, so it technically doesn't have to wait until April 1.

Conficker has been hard to kill because it can update infected machines, making it tough to spot them. The malware has spread to millions of machines through open network shares, weak passwords, and removable storage devices, such as USB sticks. The resulting botnet-like Conficker network so far hasn't acted like a botnet by waging spam runs or other attacks, but researchers are waiting for the other shoe to drop.

Because Conficker changes the way Windows responds to some network path requests, the HoneyNet Project scanner technology can detect the worm's presence by sending a legitimate request (in the form of a remote procedure call) to the machine, which triggers it to respond.

"We suggest [organizations] scan for and disinfect Conficker machines as soon as possible, regardless of speculation about what will happen on April 1," Leder and Werner say.

Meanwhile, the HoneyNet researchers have just published a research paper with their in-depth look at Conficker as part of the organization's "Know Your Enemy" series of white papers.

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About the Author(s)

Kelly Jackson Higgins, Editor-in-Chief, Dark Reading

Kelly Jackson Higgins is the Editor-in-Chief of Dark Reading. She is an award-winning veteran technology and business journalist with more than two decades of experience in reporting and editing for various publications, including Network Computing, Secure Enterprise Magazine, Virginia Business magazine, and other major media properties. Jackson Higgins was recently selected as one of the Top 10 Cybersecurity Journalists in the US, and named as one of Folio's 2019 Top Women in Media. She began her career as a sports writer in the Washington, DC metropolitan area, and earned her BA at William & Mary. Follow her on Twitter @kjhiggins.

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