Splunk/ES: dynamic drilldown searches

72345577One of the advantages of Splunk is the possibility to customize pretty much anything in terms of UI/Workflow. Below is one example on how to make dynamic drilldown searches based on the output of aggregated results (post-stats).

Even though Enterprise Security (ES) comes with built-in correlation searches (rules), some mature/eager users leverage Splunk’s development appeal and write their own rules based on their use cases and ideas, especially if they are already familiar with SPL.

Likewise, customizing “drilldown searches” is also possible, enabling users to define their own triage workflows, facilitating investigation of notable events (alerts).

Workflow 101: Search > Analytics > Drilldown

Perhaps the simplest way to define a workflow in ES is by generating alerts grouped by victim or host and later being able to quickly evaluate all the details, down to the RAW events related to a particular target scenario.

As expected, there are many ways to define a workflow, here’s a short summary of the stages listed above:

Search: here you define your base search, applying as many filters as possible so that only relevant data is processed down the pipe. Depending on how dense/rare your search is, enrichment and joins can also be done here.

Analytics: at this stage you should get the most out of stats() command. By using it you systematically aggregate and summarize the search results, which is something desirable given that every row returned will turn into a new notable event.

Drilldown: upon generating a notable event, the user should be able to quickly get to the RAW events building up the alert, enabling rapid assessment without exposing too many details for analysis right from the alert itself.

You may also want to craft a landing page (dashboard) from your drilldown search string, enabling advanced workflows such as Search > Analytics > Custom Dashboard (Dataviz, Enrichment) > RAW Events > Escalation (Case Management).

Example: McAfee ePO critical/high events

Taking McAfee’s endpoint security solution as an example (fictitious data, use case), here’s how a simple workflow would be built based on a custom correlation search that looks for high-severity ePO events.

First, the base search:

index=main sourcetype=mcafee:epo (severity=critical OR severity=high)

Next, using stats command to aggregate and summarize data, grouping by host:

| stats values(event_description) AS desc, values(signature) AS signature, values(file_name) AS file_path, count AS result BY dest

The above command is also performing some (quick) normalization to allow proper visualization within ES’ Incident Review dashboard, and also providing some quick statistics to facilitate the alert evaluation (event count, unique file names, etc).

Finally, it’s time for defining the dynamic drilldown search string based on the output of those two commands (search + stats):

| eval dd="index=main sourcetype=mcafee:epo (severity=critical OR severity=high) dest=".dest

Basically, the eval command is creating a new field/column named “dd” to store the exact search query needed to search for ePO events for a given host (dest).

In the end, putting it all together:

out1

Despite having more than 150 matching events (result) from each of those hosts, the maximum number of alerts that can be possibly generated over each correlation search execution is limited to the number of unique hosts affected.

And here’s how that translates into a correlation search definition:

cs1

cs2

Note that the “Drill-down search” value is based on a token expansion: search $dd$. This way, the value of “dd” is used to dynamically build the drilldown link.

Now, once the correlation search generates an alert, a link called “Search for raw events” should become available under “Contributing Events” after expanding the notable event details at the Incident Review dashboard.

By clicking the link, the user is directed to a new search containing all raw events for the specific host, within the same time window used by the correlation search:

cs4

Defining a “dd” field within your code is not only enabling custom dashboards development with easy access to the drilldown search (index=notable) but also standardizing the value for the drilldown search at the correlation search definition.

As always, the same drilldown search may be triggered via a Workflow Actions. Feel free to get in touch in case you are interested in this approach as well.

Happy Splunking!

 

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s