Security Experts:

Shylock Banking Trojan Upgraded Again: New Modules Boost Functionality

First discovered in 2011, the Shylock banking Trojan affects virtually all versions of Windows from Windows 2000 onward, and has turned into one of the most advanced forms of financial fraud malware around. And according to new discoveries by Symantec, Shylock has recently become even more powerful thanks to a number of new modules that significantly beef up its functionality and ability to steal money and sensitive data.

Shylock, which Symantec has creatively named “The Merchant of Malice”, currently targets more than 60 financial institutions, a majority being UK-based banks, according to Symantec.

Shylock mainly executes man-in-the-browser (MITB) attacks against a preset list of target websites in order to capture user login credentials and trick users into performing fraudulent banking transactions.

Late last year, researchers from Trusteer discovered that Shylock could detect if it is was observed within a remote desktop session or being executed locally, something that helps it evade the detection and analysis from researchers.

Earlier this year, researchers from Danish IT security firm CSIS Security Group found that Shylock was updated with new capabilities that allow it to spread and infect users over Skype

This week, researchers from Symantec have found that Shylock is now downloading and utilizing several new modules in order to beef up its functionality.

According to Symantec, modules that have been developed and are being downloaded by Shylock include:

Archiver (compresses recorded video files before uploading them to remote servers)

BackSocks (enables the compromised computer to act as a proxy server)

DiskSpread (enables Shylock to spread over attached, non-fixed, drives)

Ftpgrabber (enables the collection of saved passwords from a variety of applications)

MsgSpread (enables Shylock to spread through Skype instant messages)

VNC (provides the attacker with a remote desktop connection to the compromised computer)

Symantec also highlighted the robust infrastructure utilized by Shylock that allows for redundancy and load-balancing—something helpful when many compromised systems are simultaneously dumping data and making many connections to the command and control servers.

During periods of high traffic, Symantec explained, servers can redirect compromised computers to another server depending on the number of incoming connections.

Additionally, the infrastructure makes use of proxy servers to control the main component which maintains the pool of infected systems and provides updated configuration files and modules to infected computers.

“When a compromised computer performs one of the new, additional modules, it sends a report log to the C&C server,” Symantec explained in a blog post. “These logs are then redirected to the appropriate server using encrypted communication—the servers act as a secure socket layer (SSL) to each other.”

While Shylock has been mainly targeting users located in the UK, it is now spreading to other countries, Symantec said. “As some financial institutions become less desirable as targets, either due to increased security measures or a lack of high-value business accounts, Shylock is refocusing its attacks on those offering potentially larger returns.”

Interestingly, while Symantec describes Shylock as “one of the most sophisticated banking Trojan horse programs presently occupying the financial fraud threat landscape”, the security company lists “Trojan.Shylock” as a “Risk Level 1”, or “Very Low” risk in its Security Response database. In response to an inquiry from SecurityWeek, a Symatec spokesperson said the rating is currently in the process of being re-evaluated, but was unable to say what the new rating would be.

Symantec expects that new iterations of Shylock will continue to emerge in the wild.

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For more than 10 years, Mike Lennon has been closely monitoring the threat landscape and analyzing trends in the National Security and enterprise cybersecurity space. In his role at SecurityWeek, he oversees the editorial direction of the publication and is the Director of several leading security industry conferences around the world.