The advisory – issued on Monday – comes weeks after law enforcement announced that the Dridex botnet had been significantly disrupted as part of a global operation, and that a 30-year-old Moldovan man had been charged with being an administrator.
Researchers with Invincea are warning that Dridex activity has resumed. In a Monday email correspondence, Pat Belcher, director of security analytics at Invincea, told that the security firm has recently seen a number of localized Dridex variants targeting victims based on language and region.
“We have seen weaponized document attachments posing as RingCentral voicemails, eFaxes, USPS tracking spreadsheets, and other variants, including those that target Spanish and French speaking victims,” Belcher said. Since Oct. 22, Invincea has seen 60 instances of French users being targeted with the Dridex trojan, the advisory said. Specifically, those users had been targeted with weaponized Microsoft Office documents pretending to be receipts from retail stores and hotels.
In those attacks, the Dridex malware – which is perhaps best known for stealing banking and other credentials – was signed with digital certificates from Comodo, meaning those who whitelist signed executables are at greater security risk. Additionally, the weaponized documents use techniques that build the malware directly on the endpoint, and evade network monitoring and sandbox defenses. Despite law enforcement efforts, Belcher said Dridex is still around because the big takedown only targeted one Dridex gang. Other operators, he went on to say, simply went silent from the end of August to earlier in October.
“Once the dust settled, other Dridex gangs rushed to fill the void, using weaponized documents to spread their malware due to the ease of use to create and manage new botnets,” Belcher said. “The Dridex code is readily available on places like Pastebin and can be considered modular. Cyber criminals just need to edit a file, create a new binary that evades traditional antivirus, and hit the send button to their spam and phishing targets."