Gozi Trojan Using Dark Cloud Botnet in New Wave of Attacks

Gozi IFSB, a banking Trojan that has been making the rounds of the internet for several years, is back with new targets, new characteristics, and a new botnet for distribution. The changes, detailed by Talos Intelligence on Tuesday, serve to make the Trojan a more dangerous threat to a select group of victims.

Gozi IFSB has begun to use the Dark Cloud botnet in recent campaigns, a development that shows the attackers are moving to infrastructures that are associated with widespread criminal and malicious activity. Dark Cloud, which uses compromised personal computers as hosts for websites that change addresses every few minutes, is based primarily in Eastern Europe and Russia.

The most recent campaign uses individually targeted email messages with malicious Microsoft Word files as the delivery mechanism for the malware payload. 

"It's likely they built emails to resemble realistic email threads, appearing to reply to a victim’s previous question or request," says Talos threat researcher Holger Unterbrink, in an email interview with Dark Reading. "In other cases, they crafted email messages that are somehow related to the victims interests such as company-related information."

The level of customization indicates a high level of human involvement with the messages, rather than a mass spam email campaign. "We believe that they are using an obfuscator script/program. In many cases we looked at, they built different obfuscated docs for every single victim," says Unterbrink.

While there are a variety of different malicious payloads attached to the delivery systems, almost all are based on VBA scripts that use various methods of obfuscation and different execution patterns in attempts to evade detection in sandbox environments. Sophisticated current sandboxes and malware detection routines would almost certainly detect the activity, but simple or older technology could easily miss the operations.

Given the new payload and delivery mechanisms, what should organizations do to protect themselves from the latest wave of Gozi IFSB? "Use a multi-layer security architecture approach," says Unterbrink. "This means a mix of security protection devices/applications which are capable of communicating with each other. Companies need to realize that some attackers are using extremely sophisticated methods and/or rely on victims making mistakes (e.g. opening phishing emails). In a multi layer protected environment, even the side effects of successful attacks can be detected."

"Another important recommendation," he says, "is to focus on user education. Setup [sic] fake phishing campaigns or buy similar services to make your user aware of this threat."

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