Since build 5.2.795 it is possible to listen CLI v2 port from certain interfaces only with the following parameter in flashphoner.properties file
cli_v2.address=localhost
By defailt, CLI v2 is accessible from local interface only. Interface addresses can be comma separated
cli_v2.address=localhost,192.168.0.100
In this example, access is allowed from local interace and from internal network.
To apply settings, WCS should be restarted.