For elasticsearch prior to v2.0.0, if you want both http transport and internal elasticsearch transport to listen only on localhost simply add the following line to elasticsearch.yml file.
network.host: "127.0.0.1"
If you want only http transport to listen on localhost add the following line instead.
http.host: "127.0.0.1"
Starting from v2.0 elasticsearch is listening only on localhost by default. So, no additional configuration is needed.