A new covert attack campaign singled out multiple military and weapons contractor companies with spear-phishing emails to trigger a multi-stage infection process designed to deploy an unknown payload on compromised machines.

The highly-targeted intrusions, dubbed STEEP#MAVERICK by Securonix, also targeted a strategic supplier to the F-35 Lightning II fighter aircraft.

"The attack was carried out starting in late summer 2022 targeting at least two high-profile military contractor companies," Den Iuzvyk, Tim Peck, and Oleg Kolesnikov said in an analysis.

Infection chains begin with a phishing mail with a ZIP archive attachment containing a shortcut file that claims to be a PDF document about "Company & Benefits," which is then used to retrieve a stager -- an initial binary that's used to download the desired malware -- from a remote server.

This PowerShell stager sets the stage for a "robust chain of stagers" that progresses through seven more steps, when the final PowerShell script executes a remote payload "header.png" hosted on a server named "terma[.]app."

"While we were able to download and analyze the header.png file, we were not able to decode it as we believe the campaign was completed and our theory is that the file was replaced in order to prevent further analysis," the researchers explained.

"Our attempts to decode the payload would only produce garbage data."

What's notable about the modus operandi is the incorporation of obfuscated code designed to thwart analysis, in addition to scanning for the presence of debugging software and halt the execution if the system language is set to Chinese or Russian.

The malware is also designed to verify the amount of physical memory, and once again terminate itself if it's less than 4GB. Also included is a check for virtualization infrastructure to determine if the malware is being executed in an analysis environment or sandbox.

But if this test fails, rather than simply quitting the execution, the malware disables system network adapters, reconfigures Windows Firewall to block all inbound and outbound traffic, recursively deletes data in all drives, and shuts down the computer.

Should all these checks pass, the PowerShell stager proceeds to disable logging, add Windows Defender exclusions for LNK, RAR, and EXE files, and establish persistence via a scheduled task or Windows Registry modifications.

"Overall, it is clear that this attack was relatively sophisticated with the malicious threat actor paying specific attention to opsec," the researchers noted. "While this was a very targeted attack, the tactics and techniques used are well known and it is important to stay vigilant."