Misbehaving TCP receivers can cause internet-wide congestion collapse

An optimistic acknowledgment (opt-ack) is an acknowledgment sent by a misbehaving client for a data segment that it has not received. Whereas previous work has focused on opt-ack as a means to greedily improve end-toend performance, we study opt-ack exclusively as a denial of service attack. Specifically, an attacker sends optimistic acknowledgments to many victims in parallel, thereby amplifying its effective bandwidth by a factor of 30 million (worst case). Thus, even a relatively modest attacker can totally saturate the paths from many victims back to the attacker. Worse, a distributed network of compromised machines (“zombies”) can exploit this attack in parallel to bring about wide-spread, sustained congestion collapse. We implement this attack both in simulation and in a wide-area network, and show it severity both in terms of number of packets and total traffic generated. We engineer and implement a novel solution that does not require client or network modifications all...

• Type: Conference
• Year: 2005
• Where: CCS
• Authors: Rob Sherwood, Bobby Bhattacharjee, Ryan Braud
• Keywords: CCS 2005, Modest Attacker, Optimistic Acknowledgments, Security Privacy, Service Attack