Session replay is a form of a man-in-the-middle attack, where the intruder captures a packet sequence and modifies part of the data before forwarding it on normally. This type of attack relies on an inherent weakness in data traffic authentication.

Session hijacking is a form of a man-in-the-middle attack where the attacker takes over an IP session that’s underway by spoofing source and/or destination addressing and altering TCP sequence numbering. Typically, a packet sniffer is used to set up the hijacking by allowing the user to see the existing traffic.