As one cornerstone of Internet infrastructure, Content Delivery Networks (CDNs) work as a globally distributed proxy platform between clients and websites, providing the functionalities of speeding up content delivery, offloading web traffic, and DDoS protection. In this paper, however, we reveal that inherent nature of CDN forwarding network can be exploited to compromise service availability. We present a new class of pulsing denial of service attacks, named CDN-Convex attack. We explore the possibility of exploiting the CDN infrastructure as a converging lens, and concentrating low-rate attacking requests into short, high-bandwidth pulse waves, resulting in a pulsing DoS attack to saturate the targeted TCP services periodically. Through real-world experiments on five leading CDN vendors, we demonstrate that CDN-Convex is practical and flexible. We show that attackers can use it to achieve peak bandwidths over 1000 times greater than their upload bandwidth, seriously degrading the performance and availability of target services. Following the responsible disclosure policy, we have reported our attack details to all affected CDN vendors and proposed possible mitigation solutions.
Temporal CDN-Convex Lens: A CDN-Assisted Practical Pulsing DDoS Attack.