In a Slow Session Attack, attackers send valid TCP-SYN packets and perform TCP three-way handshakes with the victim to establish valid sessions between the attacker and victim. The attacker first establishes a large number of valid sessions then slowly responds with an ACK packet and incomplete requests to keep the sessions open for long periods of time. Normally, the attacker will set the attack to send an ACK packet with an incompleted request typically before the session time-out is triggered by the server. The “held-open” sessions can eventually exhaust the victim server’s resources used to compute this irregularity. Low-and-slow tools have also been designed to consume all 65,536 available “sockets” (source ports) resulting in a server’s inability to establish any new sessions. Slow Session Attacks are always non-spoofed in order to hold sessions open for long periods of time.
