Kademlia-based DHT has been deployed in many P2P applications and it is reported that there are millions of simultaneous users in Kad network. For such a protocol that significantly involves so many peers, its robustness and security must be evaluated carefully. In this paper, we analyze the Kademlia protocol and identify several potential vulnerabilities. We classify potential attacks as three types: asymmetric attack, routing table reflection attack and index reflection attack. A limited real-world experiment was run on eMule and the results show that these attacks tie up bandwidth and TCP connection resources of victim. We analyze the results of our experiment in three aspects: the effect of DDoS attacks by misusing Kad in eMule, the comparison between asymmetric attack and routing table reflection attack, and the distribution of attacks. More large-scale DDoS attack can be performed by means of a little more effort. We introduce some methods to amplify the performance of attack and some strategies to evade detection. Finally, we further discuss several solutions for these DDoS attacks.
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