From Known issue:
SPL-141964 - For splunktcp-ssl - we are not using it
SPL-141961 - This seems to be applicable but it states "Upgrade your older instances to the latest maintenance releases or on your 6.6.x Splunk instances. Add the following stanza to server.conf:"
sslVersions = *,-ssl2
sslVersionsForClient = *,-ssl2
cipherSuite = TLSv1+HIGH:TLSv1.2+HIGH:@STRENGTH
Can you advise what changes need to be done? I believe it is SPL-141961 but where this change need to be done IDX/HF/UF?
As you have mentioned that you are not using splunktcp-ssl on Heavy Forwarders for receiving data which means that you are not using SSL communication between UF and Heavy Forwarder. In that case I guess there will not be any problem because I have tested UF 7.0.4 with Indexer 6.5.0 and it is running fine without changing any Ciphers because in my lab I am not using SSL communication between UF and Indexer.
If you are using Deployment Server to distribute configuration to UF in this case, you need to degrade Ciphers in servers.conf sslConfig stanza because UF and Deployment Server talk with each other using SSL so there might be problem with 7.1.X Deployment server and less than 6.6 UF (as far as I am aware Ciphers changed in 6.6)
My recommendation is always upgrade test environment first, test everything and then upgrade production.