How to protect yourself from External Service Interaction?

Question

Information Security

Good afternoon. What are the ways on the part of the program code of the information system, server to protect themselves from External Service Interaction? In what ways can this be achieved? What programs exist to check for this vulnerability?

Answer 1

traffic analysis
the application is placed in an isolated environment and looks where it breaks
when http or smtp is allowed into the world, it is almost impossible to identify, only by analyzing the final destination

Answer 2

Local DNS proxy with a "white" list for resolving names and prohibiting all external outgoing connections on the server's firewall, except for the necessary ones.