345. That's How Adversaries Remove Indicators from Compromised Systems

Hello everyone!

In many cases adversaries remove artifacts from compromised systems, so today we'll look at a few examples of Indicator Removal: File Deletion (T1070.004).

And our example for today - 01flip ransomware. It has both Windows and Linux variants. Windows variant removes itself using the following command:

ping 127.0.0.7 -n 5 > Nul & fsutil file setZeroData offset=0 length=4194303 ${self_name} > Nul & Del /f /q ${self_name}

As you can see, it abuses fsutil to wipe the file. We can look for similar activity:

event_type: "processcreatewin"

AND

proc_file_path: "fsutil.exe"

AND

cmdline: ("file" AND "setzerodata")

Linux variant runs the following command:

sleep 5 && dd if=/dev/urandom of=${self_name} bs=1M count=4 > /dev/null 2>&1 && rm ${self_name} > /dev/null 2>&1

Here the adversary abuses dd, and it's another hunting oportunity:

event_type: "processcreatenix"

AND

proc_file_path: "dd"

AND

cmdline: "urandom"

See you tomorrow!

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