
The attack can be described as following:
1. Attacker sends TCP-SYN raw packet to the destination port.
2. The target OS respond with SYN/ACK packet as a part of 3-way handshake process.
3. Extracting initial sequence numbers and other information from received packet, attacker now sends the final ACK packet to complete the connection process.
Although, the process looks similar to the 3-way handshake process but remember the packets sent from attacker zone are from userland rather than OS based TCP stack.
More information is available at:
http://www.sockstress.com/
Various Press/Media coverage at:
http://www.grc.com/sn/notes-164.htm