Malware attackers are focusing on turning banking Trojans into backdoors

Malware attackers continue to recycle code from older tools into more generalized frameworks, a trend that will continue as the codebases incorporate more modularity, security experts said this week. In the latest example, the threat group behind Ursnif — aka Gozi — recently moved the tool away from a focus on financial services to more general backdoor capabilities, cybersecurity services firm Mandiant stated in an analysis. The new variant, which the company has dubbed LDR4, is likely intended to facilitate the spread of ransomware and the theft of data for extortion.

The modular malware joins Trickbot, Emotet, Qakbot, IcedID, and Gootkit, among others, as tools that started as banking Trojans but have been repurposed as backdoors, without requiring the development effort of creating an entirely new codebase, says Jeremy Kennelly, senior manager for financial crime analysis at Mandiant.

Mandiant's analysis of Ursnif points out that maintaining multiple codebases is a challenging task for malware developers, especially when one mistake could give defenders a way to block an attack and investigators a way to hunt down the attacker. Maintaining a single modular codebase is much more scalable, the company's analysis this week stated.

"In some cases, a purpose-built remote access Trojan (RAT), traditionally viewed as a backdoor, may be more conducive to the threat activity," he says. "However, a lot of threat actors want more than just a backdoor, and many commodity malware families have morphed to become multipurpose tools that simply include backdoor access."

The specialization of tools in the cybercriminal underground is also a reason why older codebases are being repurposed. By focusing specific tools on areas of attack — such as initial access, lateral movement, or data exfiltration — the developers of these tools are able to differentiate themselves against competitors and offer a unique set of features. Using existing codebases also saves time, and making such projects modular allows the tool to be customized for the customer's — read, "attacker's" — needs, says Jon Clay, vice president of threat intelligence at Trend Micro.

"The coders behind many of these toolkits create them and sell them within the cybercriminal underground markets, as they offer newbies and other malicious actors with a ready-made kit for executing attacks," he says. "Many of these offer automation now as well as GUI interfaces to manage the attacks and victim information/data."