A Survey on CDN Vulnerability to DoS Attacks

Content Delivery Networks (CDN), or ”content distribution networks” have been introduced to improve performance, scalability, and security of data distributed through the web. To reduce the response time of a web page when certain content is requested, the CDN redirects requests from users’ browsers to geographically distributed surrogate nodes, thus having a positive impact on the response time and network load. As a side effect, the surrogate servers manage possible attacks, especially denial of service attacks, by distributing the considerable amount of traffic generated by malicious activities among different data centers. Some CDNs provide additional services to normalize traffic and filter intrusion attacks, thus further mitigating the effects of possible unpleasant scenarios. Despite the presence of these native protective mechanisms, a malicious user can undermine the stability of a CDN by generating a disproportionate amount of traffic within a CDN thanks to endless cycles of requests circulating between nodes of the same network or between several distinct networks. We refer in particular to Forwarding Loops Attacks, a collection of techniques that can alter the regular forwarding process inside CDNs. In this paper, we analyze the vulnerability of some commercial CDNs to this type of attacks and then propose some possible useful defensive strategies.