What a crazy oversight, right? This isn't just some authenticated port that you can't do anything with or something someone would ever actually normally connect to from the outside. No, this thing opens up a very direct tunnel into the java server to the whole network using the Splunk custom command protocol. What?!?!
Splunk has been negatively impressing me regarding everything surrounding custom search commands (the DB Connect commands are implemented as such) and DB Connect is an especially hard-to-predict-hard-to-debug example.
While I can't answer your question directly, I can tell you what didn't work for me. I was hoping that setting the vmopts option -Daddress=127.0.0.1 or -Dserver.address=127.0.0.1 would help, since that's what works for some Spring Boot applications (which I'm not sure DB Connect is, but it might be).
Perhaps firewalling would work or network namespaces/containerization.
