312. Hunting for Certutil Abuse

Hello everyone!

Let's talk about another legitimate utility, which is commonly abused by adversaries and is a great target for hunting. I'm talking about certutil.

It's usually used to obtain certificate authority information and configure Certificate Services. But adversaries use it to solve other tasks, of course. And here's an example:

certutil.exe -decode C:\Windows\..\ProgramData\bEyjSIpZvbJpjVv9.a9oc C:\Windows\..\ProgramData\hkNlPHP61rvE0T7J.lpxQ

So, here the adversary uses the tool to decode the payload, but it's not the only case. Threat actors may also use it to download or encode data. Let's build a query based on all the cases:

event_type: "processcreatewin"

AND

proc_file_path: "certutil.exe"

AND

cmdline: ("decode" OR "encode" OR "url" OR "urlcache" OR "verifyctl")

See you tomorrow!

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