Threat hunting without file names

Having signatures for common techniques is great but let's take it to the next level. Imagine if a script executable is simply copied with a new name, will your dectection still trigger? This is a good technique to keep in mind while creating searches.

Take a look at the following Splunk search to detect mshta.exe with suspicious strings.



Works great, lasts a long time right, but a central match is the mshta.exe string.

Here is another version which negates the mshta.exe to catch just those where the file has been renamed, which in my view would be a higher severity and I want to see those separately.



Here is another example to find the -accepteula string from sysinternals psexec.




This one is a bit noisier but it can be filtered.


Testing with edrs is surprisingly easy with command line detections, just paste your target string in a command window and wait for the SIEM to update. The executables don't actually have to be there and it doesn't matter if the command works or not.

Next time you find a bunch of suspicious strings evaluate if they are good enough just to test for on their own. You would hate to miss something due to just a filename.


References:
https://twitter.com/cyb3rops/status/1130747925242482688
https://twitter.com/ch33kyf3ll0w/status/816319597645328384

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