Smart Scan checks network connections so it’s possible Norton sees a vulnerability. Does N360 identify the accessible folder? Is it possible you gave that folder special permission lowering its security?
Yours is a different issue from the WAN access vulnerability discussed on another thread but maybe there’s useful info. A network issue detected id vulnerability: HNS-WAN-ACCESS
If you’re concerned about port exposure, one way to check is test them using GRC ShieldsUp. Read the information at that site. In addition to the first 1055 service ports, you can run custom probe for ports above 1055. Instructions here. Tracking thread for the new version 25.xx release - #32 by Puzzler