Splunk uses HTTP 303 redirects if you call /. curl command with -L switch should have result different.
Anyway, since you are getting this reply, it proves that Splunk is listening port 80 and there is no firewall issue.
If you cannot access interface outside of VM, you may check your VM network interface settings on your virtualization host.
If this reply helps you an upvote and "Accept as Solution" is appreciated.
