Splunk publishes the checksum for the MD5 hash via the downloads page for the particular download you requested.
Here's a screen shot of the page and were to find the MD5 link.
Just do the steps
1. click on free splunk
2. click on uf
3. click on older versions
4. click on download
5. click on download md5
For Splunk 6.5.2 follow this link:
https://www.splunk.com/en_us/download/universal-forwarder/thank-you-universalforwarder.html