TCP/IP Hijacking :
TCP/IP hijacking is a clever technique that uses spoofed packets to take over a connection between a victim and a host machine. This technique is exceptionally useful when the victim uses a one-time password to connect to the host machine. A one-time password can be used to authenticate once and only once, which means that sniffing the authentication is useless for the attacker.
To carry out a TCP/IP hijacking attack, the attacker must be on the same network as the victim. By sniffing the local network segment, all of the details of open TCP connections can be pulled from the headers. As we have seen, each TCP packet contains a sequence number in its header. This sequence number is incremented with each packet sent to ensure that packets are received in the correct order. While sniffing, the attacker has access to the sequence numbers for a connection between a victim (system A in the following illustration) and a host machine (system B). Then the attacker sends a spoofed packet from the victim’s IP address to the host machine, using the sniffed sequence number to provide the proper acknowledgment number.
The host machine will receive the spoofed packet with the correct acknowledgment number and will have no reason to believe it didn’t come from the victim machine.