Famed Internet search engine Shodan now offers a free scanning tool that hunts down systems on the Internet that are controlling malware-infected computers.

The new Malware Hunter crawler, unveiled today, is the result of a project that began in 2015 by Recorded Future and Shodan that roots out remote access Trojan (RAT) operations by detecting computers on the Internet that are serving as RAT command-and-controllers (C2s) in botnets. It's an alternative to the traditional, more passive collection approach of honeypots, VirusTotal, and some malware analysis, to extrapolate cybercrime and cyber espionage malware attacks.

RATs are the backdoor malware used by attackers to remotely control infected machines. They log keystrokes and can record audio and video of the machine.

Shodan Malware Hunter scans ports on the Internet for servers, routers, webcams, and other connected devices in search of RAT controller IP addresses with the goal of catching them before they infect their victims. The tool employs RAT controller probes that then are matched against known RAT signatures. To date, Malware hunter has identified one large global network of thousands of GhostRAT controllers as well as the C2s of other infamous RATs such as Dark Comet, njRAT, and Poison Ivy.

"It's sending specific requests to hosts on the Internet and looking for a specific response back" that detects a RAT controller, explains Levi Gundert, vice president of intelligence and strategy at threat intelligence firm Recorded Future.

Shodan itself basically crawls the Internet for publicly accessible computers and devices, and is a popular tool among security researchers. John Matherly, founder of Shodan, launched the search engine in 2009 as an open-source project for searching devices on the Internet. 

Matherly explains that Malware Hunter poses as a newly infected client machine while searching the Internet for command-and-control servers, and makes rooting out C2s much faster than passive methods.

"We've already seen that this technique can help identify malicious operations before they're widely deployed," Matherly said via an email interview. "However, there's still a lot of work that has to be done after a C2 has been identified, which is what I assume a lot of law enforcement time is spent on."

Renowned researcher HD Moore says Shodan's new Malware Hunter could streamline the detection of Internet-connected command-and-control systems. "It has the potential to find all of the Internet-connected C2s in one shot as opposed to waiting for the installations to download new lists," Moore says.

But more sophisticated attackers are adopting obfuscation techniques to evade detection by these types of scans, he says. "I would expect this [Malware Hunter] to work pretty well in the short-term and less so as the malware operators get more sophisticated."

Moore worked on a similar scanning project with an antivirus company while he was with Rapid7, and the scans were lucrative for spotting C2s. But attackers started to hide their tracks once they got caught up in Rapid7's scans, he says. "This kind of scanning is decent for the status quo, but we are seeing C2s move towards more complicated and obfuscated backends to avoid scans," says Moore, who pioneered much of the Internet-scanning research looking for exposed devices and systems. His research led to Project Sonar, a community project founded in 2013 for sharing Internet-scanning data, tools, and analysis. 

Recorded Future's Gundert notes that some of the RAT families listed in Shodan employ obfuscation, so the tool can spot even the stealthy C2s. "The project started with the low hanging fruit - Black Shades, Dark Comet, njRAT - and more recently. families like Gh0st RAT were added, which involved longer analysis," Gundert says. 'Ultimately, every family is possible to emulate to elicit a controller response; it's just a matter of time and persistence."

Shodan finds between 400- and 600 RAT controllers per day, according to data compiled by Recorded Future.

"Not all RAT operators are super-sophisticated," however, Gundert notes. "Some run command-and-control from their home computers; we see ... IP addresses sitting on residential networks worldwide."

Meanwhile, the new tool is yet another example of how Shodan is evolving its search engine to provide more intelligence and insight into Internet-connected devices. "We've done similar things in other areas - Tor, ICS, BitTorrent - and this is another part of the ongoing mission at Shodan to provide greater insights about the Internet," Matherly says.

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