Researcher Unmasks Sneaky Clampi Trojan at Black Hat

At the Black Hat security conference in Las Vegas, SecureWorks researcher Joe Stewart discusses his analysis of the Clampi Trojan, which has remained largely under the radar outside security circles despite infecting hundreds of thousands of users. According to Stewart, the group behind Clampi is running one of the most sophisticated Trojan criminal operations on the Internet.

A security researcher has uncovered new details on the malware behind one of the largest ongoing cyber-crime operations on the Internet.

Known alternatively as the Clampi, Ligats or Ilomo Trojan, the malware is believed to have been infecting computers since 2007. Today, it is believed to have swiped data from hundreds of thousands of Windows users as it seeks out information that can be used to log in to 4,600 banking and other sites that interest cyber-crooks.

"This is a pretty vast net that they're throwing out here," said Joe Stewart, director of malware research for the Counter Threat Unit at SecureWorks. "We're used to seeing things like Zeus, where you see 20 or 30 banks maybe that they usually target."

Its persistence is rivaled by its sneakiness. Like Coreflood, the malware uses the SysInternals PsExec tool to spread once a domain administrator logs on to an infected workstation. The malware authors added this functionality in March.

"Once it gets a foothold on one system, they use this PsExec tool once they have domain administrator credentials, where they can just push the malware out to every machine on the network," Stewart said.

The malware is also spreading via drive-by attacks on compromised Websites.

"They basically have stolen FTP credentials to these sites, and they are getting those from the victims they have already infected," he said. "So it's a vicious cycle here."

So far, Stewart has identified 1,400 of the Websites, which range from banking sites to advertising networks to news blogs.

The traffic sent by Clampi to its command-and-control server is encrypted by 448-bit blowfish encryption, using a randomly generated session key sent to the control server with 2048-bit RSA encryption. SecureWorks penetrated the encryption by intercepting the session key in a test system and decrypting the network traffic. This enabled Stewart to analyze the list of Websites targeted by Clampi's LOGGER module.

According to SecureWorks, the configuration consists of a list of CRC32 checksums of host names, paths and ports for Clampi to examine when determining whether to send the HTTP request data back to the controller.

Not much is known about who is behind Clampi, though it is thought to be operated by a botmaster based in Eastern Europe, Stewart said. Still, he noted that most major anti-virus vendors are detecting Clampi variants.

Given the lag between the release of a new Trojan and its detection, SecureWorks recommends that businesses that carry out online banking and financial transactions use a dedicated workstation for accessing financial accounts that is isolated from the rest of the local network and the Internet except for necessary financial sites. Businesses should also consider hardening their systems against auto-run-type threats since Trojans often spread through removable drives.

"It's definitely more of an advanced operation than most of the Trojan criminal operations that we've seen," Stewart said.