217. Detecting PXA Stealer's Behavior Markers

Hello everyone!

Let's talk about stealers again. This time about PXA stealer. It's a Python-based stealer emerged in in late 2024.

Let's look at a few behavior markers covered in a joint report by SentinelOne and Beazley Security.

The first one - misusing certutil.exe to to decode a masquaraded file into a new encrypted archive:

certutil -decode Document.pdf Invoice.pdf

It's not common for this utility to decode PDF files, so we can use it to build our logic:

event_type: "processcreatewin"

AND

proc_file_path: "certutil.exe"

AND

cmdline: ("decode" AND *pdf)

The next behavior - abusing renamed WinRAR executable to unpack the archive:

images.png x -ibck -y -poX3ff7b6Bfi76keXy3xmSWnX0uqsFYur Invoice.pdf C:\\Users\\Public

Of course, here we can hunt for renamed executables:

event_type: "processcreatewin"

AND

proc_file_originalfilename: "WinRAR.exe"

AND NOT

proc_file_path: *winrar*

Make sure to check the report - you can find more interesting behaviors!

See you tomorrow!

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