292. Hunting for PhantomVAI Loader's Behaviors

Hello everyone!

Today we'll look at PhantomVAI Loader, and various related behavior markers we can transform into hunting queries.

Let's start from the delivery stage. The adversary distributed archives with malicious JS or VBS files via spear phishing emails. We can hunt for wscript.exe executing files from folders related to user downloads, for example:

event_type: "processcreatewin"

AND

proc_file_path: "wscript.exe"

AND

cmdline: ("downloads" OR "content.outlook")

It executes the following PowerShell command to download the next stage:

"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe" -nop -w hidden -c "$disjoined = '[redacted]' -replace '','';$isogonism = [System.Text.Encoding]::Unicode.GetString([Convert]::FromBase64String($disjoined));Invoke-Expression $isogonism;"

Here, for example, we can look for decoding:

event_type: "processcreatewin"

AND

proc_file_path: "powershell.exe"

AND

cmdline: ("unicode.getstring" AND "frombase64string" AND "invoke-expression")

Also, it spawns MSBuild.exe in order to inject the payload into it. And it's another hunting opportunity:

event_type: "processcreatewin"

AND

proc_p_file_path: "powershell.exe"

AND

proc_file_path: "msbuild.exe"

See you tomorrow!

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