Networks & Defense
Man-in-the-Middle
Also: MITM, on-path attack
An attacker who sits between two parties and can read or change what passes between them.
In more detail
On an unprotected connection, anyone who controls a router, a Wi-Fi network or a proxy on the path can watch or alter traffic. TLS defeats this by encrypting the traffic and by making the server prove its identity, so a middle party cannot present a certificate the client accepts. The defence collapses if certificate checks are disabled.