Splunk Search

DNS tunneling detection - Help with fine tuning splunk search

Woodpecker
Path Finder

Hey Splunkers,

Can someone please help me with the logic, how can I finetune the search below to detect DNS tunnelling? The one here is too noisy.. or if a better SPL is available that can be used instead.

 

 

| tstats `security_content_summariesonly` dc("DNS.query") as count from datamodel=Network_Resolution where DNS.message_type=QUERY by DNS.src,DNS.query
| rename DNS.src as src DNS.query as message 
| eval length=len(message) 
| stats sum(length) as length by src 
| append 
    [ tstats `security_content_summariesonly` dc("DNS.answer") as count from datamodel=Network_Resolution where DNS.message_type=QUERY by DNS.src,DNS.answer
    | rename "DNS.src" as src "DNS.answer" as message 
    | eval message=if(message=="unknown","", message) 
    | eval length=len(message) 
    | stats sum(length) as length by src ] 
| stats sum(length) as length by src | where length > 100

 

 

Thanks!

0 Karma

FrankVl
Ultra Champion

Only looking for devices that show a high volume (in bytes rather than count) of unique DNS requests/responses will indeed probably cause a lot of noise.

Take a look at these articles to take a more advanced approach to this:

https://lantern.splunk.com/Security/Use_Cases/Threat_Hunting/Monitoring_a_network_for_DNS_exfiltrati...

https://www.splunk.com/en_us/blog/security/hunting-your-dns-dragons.html

One of the key tricks discussed there is to also look at the entropy of the domains occuring in the query. Long, high-entropy sub-domain names are a good indicator someone is trying to hide data in DNS messages.

0 Karma
Get Updates on the Splunk Community!

Index This | What did the zero say to the eight?

June 2025 Edition Hayyy Splunk Education Enthusiasts and the Eternally Curious!  We’re back with this month’s ...

Splunk Observability Cloud's AI Assistant in Action Series: Onboarding New Hires & ...

This is the fifth post in the Splunk Observability Cloud’s AI Assistant in Action series that digs into how to ...

Now Playing: Splunk Education Summer Learning Premieres

It’s premiere season, and Splunk Education is rolling out new releases you won’t want to miss. Whether you’re ...