The popular Dridex banking trojan has been modified by attackers to bypass a fundamental protection on Windows that lets users block the installation of potentially malicious programs, according to security firm Flashpoint.
The modification, which first appeared on January 25, allows the program to silently execute on systems where the user is part of an administrative group, according to Vitali Kremez, senior cyber-crime intelligence analyst at Flashpoint, a threat intelligence firm. The attack by itself does not escalate privileges and so may not work on limited user accounts.
“Normally, Windows prompts a user to run an application, but by bypassing that, Dridex allows the actors to silently execute its code without ever alerting the user,” Kremez told eWEEK.
Dridex is one of the top-5 programs used by online criminals to gain access to victims’ financial accounts. Dridex is the fourth most encountered banking trojan, accounting for 11 percent of financial malware encountered by IBM’s X-Force research labs.
The top threat is Zeus and Zeus-based malware, accounting for 28 percent, with Neverquest and Gozi following in second and third place holding 17 percent and 16 percent shares of encounters.
While Dridex’s popularity peaked between 2014 and 2015, Flashpoint has seen smaller campaigns throughout 2016. In January 2017, the company detected another campaign targeting financial institutions in the United Kingdom with the new UAC bypass feature, the company said.
Dridex typically hitchhikes inside of a Word document using macros to execute. Victims that download the document and then open it are exposed to the trojan. Once a system is infected, Dridex quickly moves to capture additional information from the user to help defeat the variety of methods that financial institutions use to attempt to stop fraud.
“After malware infection, the Dridex ‘token grabber’ and ‘webinject’ modules allow the fraud operators to quickly request any additional information that is required to subvert authentication and authorization challenges imposed by anti-fraud systems at financial institutions,” Kremez said in a blog post.
“The fraud operators are able to create a custom dialog window and query the infected victims for additional information as if it was sent from the bank itself.”
Dridex works on Windows 7, but has not yet been tested on Windows 10, Kremez said. On those systems, Dridex takes advantage of Windows 7’s automatic elevation of certain applications to minimize the UAC dialogs presented to a user.
While ransomware has become the most popular financial attack, security firms continue to encounter banking trojans. IBM, for example, has seen an uptick in infections by Zeus Sphinx, which targeted financial customers of more than 33 Canadian banks and 40 Australian banks in January.
Cyber-criminals have also moved upstream, infiltrating banks and using the SWIFT financial messaging and transaction network to move money. In February 2016, $81 million was stolen from the Bangladesh Central Bank by cyber-criminals who had compromised member financial institutions.