An adversary targets the communication between two components (typically client and server), in order to alter or obtain data from transactions. A general approach entails the adversary placing themself within the communication channel between the two components.

Whenever one component attempts to communicate with the other (data flow, authentication challenges, etc.), the data first flows through the adversary, who has the opportunity to observe or alter it, before being passed on to the intended recipient as if it was never observed. This interposition is transparent leaving the two compromised components unaware of the potential corruption or leakage of their communications. The potential for these attacks yields an implicit lack of trust in communication or identify between two components.

These attacks differ from Sniffing Attacks (CAPEC-157) since these attacks often modify the communications prior to delivering it to the intended recipient.