054. Detecting CypherIT Crypter Behaviors

Hello everyone! I think it's not a secret that many adversaries leverage crypters to evade defenses. But some crypters not only encrypt and obfuscate maicious code, but also have intersting behaviors we can use for detection engeneering!

Let's look at CypherIT - a very popular crypter, which used to be sold on underground resources, and used by lots of various threat actors worldwide (for example, Sticky Werewolf).

The first behavior example we'll look at is abusing findstr for AV discovery:

findstr /I "opssvc wrsa"

findstr "bdservicehost AvastUI AVGUI nsWscSvc ekrn SophosHealth"

To detect it, search for findstr executions with AV/EDR names in command line (you can expand this list, of course):

event_type: "processcreate" 

AND 

proc_file_name: "findstr.exe" 

AND 

cmdline: (*wrsa* OR *opssvc* OR *avastui* OR *avgui* OR *nswscsvc* OR *sophoshealth* OR *bdservicehost* OR *ekrn*)

Next noteworthy behavior - dropping and executing renamed AutoIt interpreter to run a malicious script, for example:

Philip.com N

Renamed AutoIt executions are not very common for corporate environments, so we can build detection logic based on this feature:

event_type: "processcreate" 

AND

proc_file_originalfilename: "AutoIt3.exe" 

AND NOT

proc_file_name: "autoit3.exe"

As always, there are more! Try to find it, here's a sample for you. See you tomorrow!