12.1.5 is the latest
here is the release notes
New fixes and features in Symantec Endpoint Protection and Network Access Control 12.1.5
http://www.symantec.com/business/support/index?page=content&id=TECH224706
all other information like suppoted upgrade path, fixes, all covered here, please go through all the links
https://www-secure.symantec.com/connect/blogs/symantec-released-symantec-endpoint-protection-121-release-update-5-1215