A brand new variant of the Agent Tesla malware has been noticed delivered through a lure file with the ZPAQ compression format to reap knowledge from a number of e mail purchasers and practically 40 internet browsers.
“ZPAQ is a file compression format that gives a greater compression ratio and journaling operate in comparison with broadly used codecs like ZIP and RAR,” G Information malware analyst Anna Lvova stated in a Monday evaluation.
“That implies that ZPAQ archives will be smaller, saving space for storing and bandwidth when transferring recordsdata. Nevertheless, ZPAQ has the largest drawback: restricted software program assist.”
It is usually used as a first-stage payload, offering distant entry to a compromised system and utilized to obtain extra subtle second-stage instruments resembling ransomware.
Agent Tesla is usually delivered through phishing emails, with current campaigns leveraging a six-year-old reminiscence corruption vulnerability in Microsoft Workplace’s Equation Editor (CVE-2017-11882).
The most recent assault chain begins with an e mail containing a ZPAQ file attachment that purports to be a PDF doc, opening which extracts a bloated .NET executable that is largely padded with zero bytes to artificially inflate the pattern measurement to 1 GB in an effort to bypass conventional safety measures.
“The primary operate of the unarchived .NET executable is to obtain a file with .wav extension and decrypt it,” Lvova defined. “Utilizing generally used file extensions disguises the visitors as regular, making it tougher for community safety options to detect and stop malicious exercise.”
The top objective of the assault is to contaminate the endpoint with Agent Teslathat’s obfuscated with .NET Reactor, a reliable code safety software program. Command-and-control (C2) communications is achieved through Telegram.
The event is an indication that risk actors are experimenting with unusual file codecs for malware supply, necessitating that customers be looking out for suspicious emails and preserve their techniques up-to-date.
“The utilization of the ZPAQ compression format raises extra questions than solutions,” Lvova stated. “The assumptions listed below are that both risk actors goal a selected group of people that have technical data or use much less broadly recognized archive instruments, or they’re testing different strategies to unfold malware sooner and bypass safety software program.”