The Retefe banking Trojan has resumed its activity with a new series of attack campaigns that leverage Smoke Loader as an intermediate loader.
Proofpoint observed that the malware returned to regular attacks against German and Swiss users in April 2019 after taking a hiatus in 2018. These campaigns helped reveal several new techniques now employed by the banking Trojan. One geographically targeted campaign against Switzerland, for instance, used an Object Linking and Embedding (OLE) package to deliver Smoke Loader. This threat, in turn, downloaded Retefe two hours after infection.
The banking malware incorporated other changes as well. One operation detected by Proofpoint abused a shareware application to run an executable and a Python script. This code, in turn, wrote two files: convert-pdf-to-word-plus.exe and convert-pdf-to-word-plus_driver.exe. The former was a legitimate installer for the Convert PDF to Word Plus application that’s executed as a decoy, while the latter acted as a Retefe loader.
In another campaign, the malware turned away from Tor toward a stunnel, most likely in a bid to cause less noise in an enterprise environment and thereby avoid detection.
Looking to the Past of Retefe
This resurgence of Retefe comes after a busy period several years ago. In June 2016, Avast observed the malware using fake certificates to target U.K. banking customers and steal their login credentials. More than a year later, Proofpoint discovered the banking Trojan leveraging EternalBlue, the same exploit used by WannaCry ransomware, to move laterally through a network following the initial infection of a victim.
How to Defend Against a Banking Trojan
Security professionals can defend against banking Trojans like Retefe by using ahead-of-threat detection to discover potentially malicious domains before threat actors take advantage of them in attacks. Security teams should also use tools such as VBA editor to inspect the macro code in Microsoft Office documents for signs of malicious functionality.