"User Documents Overwritten With Malicious Code in Recent Dridex Attacks on macOS"
Security Researchers at Trend Micro have found that the cybercriminals behind the Dridex banking trojan have adopted a new tactic in recent attacks targeting macOS devices, overwriting the victim’s document files to deliver their malicious code. Dridex has been active since at least 2012 and is considered one of the most prevalent financial threats. Dridex survived a takedown attempt in 2015 and remained operational after receiving various updates. In 2019, the Department of Homeland Security (DHS) warned of continuous Dridex attacks targeting financial institutions. According to the researchers, a recently observed Dridex attack targeting macOS stood out because of a novel tactic employed to disguise the malicious Microsoft Word document used for malware delivery. The researchers noted that the attackers distribute a Mach-o executable file that is designed to search for .doc files in the current user directory and write malicious macro code to all of them in plain hexadecimal dump, not in content. The researchers stated that while the macro feature in Microsoft Word is disabled by default, the malware will overwrite all the document files for the current user, including the clean files. This makes it more difficult for the user to determine whether the file is malicious since it doesn’t come from an external source. The researchers explained that the malicious embedded document was not new, first observed in the wild in 2015. The analyzed Mach-o file sample was first submitted to VirusTotal in 2019. The researchers stated that analysis of the overwritten documents revealed the inclusion of an AutoOpen macro meant to call several functions with normal-looking names but which were meant to perform nefarious actions. The payload delivered by the macro was an .exe file meant to fetch the Dridex loader. While the .exe file would not run on macOS, the analyzed variant might be in testing stages and could later be converted to fully work on macOS. The researchers concluded that currently, the impact on macOS users for this Dridex variant is minimized since the payload is an exe file (and therefore not compatible with macOS environments). However, it still overwrites document files which are now the carriers of Dridex’s malicious macros. Furthermore, it’s possible that the threat actors behind this variant will implement further modifications that will make it compatible with macOS.