Splunk Enterprise Security
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Is it possible to use a comparison / conditional functions with a lookup?

Communicator

Hello,

I’d like to create an alert on ransomware detections. I have file events logs and their most important field is ‘file_name’. It looks like this:

File_name
File1.txt
File2.pdf
File3.xls
Etc.

At the same time I have a lookup called ‘ransomware_extensions’ with only one column ‘extension’ which contains ransomware extensions. It looks like this:

Extension
.wtf
.exx
.locked
Etc.

I’m trying to create a search which checks if ‘file_name’ value matches an ‘extension’ value. Something like that one:

*my basic search
| eval ransomware=if(like(file_name,"%[|lookup ransomware_extensions.csv extension output extension]%"), 1, 0)

Unfortunately it doesn’t work.

Do you have any ideas?

Regards,
Alexey.

0 Karma
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Re: Is it possible to use a comparison / conditional functions with a lookup?

Motivator

You should check the ES content updates app (https://splunkbase.splunk.com/app/3449/). It has a story (with searches included) on ransomware.

But from what you have, you can try to extract the file extension from you file_name and then use a lookup with

extension, ransomware
exx, true

in your search use

|lookup ransomware_extensions.csv extension output extension ransomware

OR make it and automatic lookup.
this way you can search ransomware="true"

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Hope I was able to help you. If so, an upvote would be appreciated.
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Re: Is it possible to use a comparison / conditional functions with a lookup?

Communicator

Yep, this is a solution, didn't think about it.

Thanks for the answer !

0 Karma
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Re: Is it possible to use a comparison / conditional functions with a lookup?

Ultra Champion

Populate your ransomware extension lookup with *.ext and set the match_type of that field of the lookup to WILDCARD. That way you can match the entire filename against the extension patterns in the lookup.

And as @diogofgm mentions, you can then use the lookup (either automated or as part of your search) to add a field ransonware = true/false to your results which can then be used to filter.

View solution in original post

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Re: Is it possible to use a comparison / conditional functions with a lookup?

Communicator

Probably the easiest way to solve the issue. Will try it.

Thanks for the advice!

0 Karma