RST hijacking is a TCP session hijacking technique emphasized in CEH materials under network attacks against established communications. In TCP, a Reset flag packet is used to abruptly tear down a connection. If an attacker can observe the session and determine the correct parameters such as IP addresses, ports, and an in-window sequence number, they can forge a TCP RST packet that appears to come from one endpoint. This can force the victim side to drop the session, making the legitimate client suddenly lose responsiveness.

The key clue in the scenario is that Rachel “observes a client-server communication” and then injects crafted packets that disrupt the client while the server continues to communicate with Rachel’s system. That behavior matches the practical use of RST hijacking in demonstrations: terminate or desynchronize the victim endpoint while keeping the server-side session usable long enough for the attacker to inject traffic with valid sequence and acknowledgment values. In a switched LAN, this is often paired with sniffing or traffic visibility to reliably craft the reset packet and subsequent injected packets.

Blind hijacking is different because the attacker cannot see the traffic and must guess sequence numbers, which contradicts the “observes communication” detail. UDP hijacking is not applicable because UDP is connectionless and does not use session state or RST flags. “TCP/IP hijacking” is a broad category, but the question asks for the specific technique used to disrupt the client via crafted packets, which is best identified as RST hijacking.