A spoofing attack, in computer security terms, refers to a situation in which one person or program is able to masquerade successfully as another.
ÂÂ
An example from cryptography is the man in the middle attack, in which an attacker spoofs Alice into believing he's Bob, and spoofs Bob into believing he's Alice, thus gaining access to all messages in both directions without the trouble of any cryptanalytic effort.
ÂÂ
The attacker must monitor the packets sent from Alice to Bob and then guess the sequence number of the packets. Then the attacker knocks out Alice with a SYN attack and injects his own packets, claiming to have the address of Alice. Alice's firewall can defend against spoof attacks when it has been configured with knowledge of all the IP addresses connected to each of its interfaces. It can then detect a spoofed packet if it arrives from an interface that is not known to be connected to that interface.
