Both the Carberp and Zeus malware families caused major havoc for banks and users alike, but in recent years, crackdowns on cybercrime discussion boards and the Dark Web marketplace pushed these threats out of the spotlight. Now, a more sophisticated mashup has emerged: the Bolek banking Trojan.

Borrowing a bit of code from both attack vectors and tossing in some of its own for good measure, Bolek is spreading quickly. Russian banks, Polish bitcoin sites and Canadian online banking portals have all recently come under attack.

Successful Successor

Based on its target capabilities and feature set, Bolek is adopting a “go big or go home” approach to banking fraud. As noted by SecurityWeek, the new malware not only targets both 32-bit and 64-bit versions of Windows, but can perform everything from webinjections to traffic interceptions, keylogging and credentials theft. It’s also possible for malicious actors to configure worm-like behavior in Bolek since the banking Trojan can receive updates that alter its functionality based on infection success and security response.

According to Softpedia, there are clear ties to both Carberp and Zeus: From Carberp, Bolek borrowed the architecture for a custom virtual file system used to hide key files from on-board security systems. From Zeus, it grabbed the robust webinjection mechanism, which makes it possible for cybercriminals to hijack browser processes and compromise entire webpages when users visit online banking portals.

Security firm Dr. Web claimed that “the main purpose of Trojan.Bolik.1 is to steal confidential information.” This aim is facilitated by both keeping C&C domains in runtime memory values and using elliptic curve cryptography to ensure all exfiltrated data is protected.

The Bolek Banking Trojan: Beyond Banks

As noted by security firm PhishMe, infrastructure used by the Bolek banking Trojan is being leveraged to distribute Android device malware. While the new banking attacks, telecom breaches and mobile malware infections are all under the control of a single operator or group, no one has come forward to claim responsibility.

With both Zeus and Carberp source code available, it’s entirely possible that Bolek’s basic structure is making the rounds on the Dark Web and being repurposed by innovative malware-makers. Ultimately, that’s the most worrisome piece of this puzzle: While novice-level attackers have access to prebuilt packages on the Dark Web, there is also a separate set of malware innovators willing to do more than exploit the status quo.

With the ability to initiate remote desktop protocol (RDP) connections and import persistent .dll files to trick devices into accepting the code as legitimate, the Bolek banking Trojan is a first look at the next iteration of financial malware: custom-built code that cherry-picks the best features from previous generations to create digitally superior offspring.