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This reminds me of the Slowloris [https://en.wikipedia.org/wiki/Slowloris_(computer_security)] attack that takes advantage of web servers that can't handle a lot of open connections. I haven't tested to see how vulnerable Splunk is but I would seriously consider placing some kind of reverse proxy in front of any user-facing services. I'm sure nginx is a popular option for this but if you already have F5 load balancers you may be able to use HTTP and OneConnect profiles to separate the client and server side connections. I'm sure other load balancers have similar options.
I would suggest that you look at how to report a possible vulnerability at https://www.splunk.com/page/securityportal. Report it there, and the ProdSec team will review as needed and get back to you.