Imagine you have a simple GET request going to server 123.456.111.222. Your client executable creates a winsock on the server IP (TCP) and sends the HTTP request (unencrypted) to the server. If a local program found the outgoing request and specifically the source port of the request, could that program send its own data to that port? (Hopefully winning the race condition, but it should given it's localhost)
I would get the source port by using GetExtendedTcpTable however I am not quite sure if it would be as simple as opening the port using winsock and sending the data.