A new phishing campaign is active in the wild, targeting users with BazarBackdoor malware. The campaign evades email security checks to deliver the malware by exploiting nested RAR and ZIP files.
Phishing Campaign Distributing BazarBackdoor Malware
Researchers from Cofense have uncovered a new phishing campaign infecting users with BazarBackdoor malware. As elaborated in their report, this campaign employs new tactics to evade Secure Email Gateway (SEG) and deliver the malware.
Specifically, the attack begins when the target recipient receives an email with an archive (.rar or .zip) as an attachment. Believing the content of the email, the user would potentially open the zipped file that contains the malware.
At this point, the campaign utilizes a nested or multi-compression technique to bypass security checks. Doing so makes the SEGs pass the attachment as safe after failing to assess them adequately. As stated in the post,
The nesting of various archive types is purposeful by the threat actor as it has the chance of hitting the SEG’s decompression limit or fails because of an unknown archive type.
In the sample email that the researchers shared, the attacker delivered a heavily obfuscated JavaScript file within the archive.
De-obfuscation can be a limit within a SEG as well, meaning that if there are multiple layers of encryption surrounding a payload, a SEG might only go so many layers deep before labeling the binary as benign.
That’s how the malware would reach the victim’s mailbox.
Upon opening the attachment, the JavaScript would download the payload as a .png file where the BazarBackdoor resides.
In brief, BazarBackdoor is a trojan belonging to the authors of TrickBot, which paves the way for another malware to control the target device. Upon infecting a device, the trojan may even download the Cobalt Strike toolkit to take over the entire network. This trojan may also lead to devastating ransomware attacks in the worst scenario.