Exit from Hell? Reducing the Impact of Amplification DDoS Attacks

Marc Kührer, Thomas Hupperich, Christian Rossow, Thorsten Holz

23rd USENIX Security Symposium, San Diego, CA, USA, August 2014


Abstract

Amplification vulnerabilities in many UDP-based network protocols have been abused by miscreants to launch Distributed Denial-of-Service (DDoS) attacks that exceed hundreds of Gbps in traffic volume. However, up to now little is known about the nature of the amplification sources and about countermeasures one can take to remediate these vulnerable systems. Is there any hope in mitigating the amplification problem?

In this paper, we aim to answer this question and tackle the problem from four different angles. In a first step, we monitored and classified amplification sources, showing that amplifiers have a high diversity in terms of operating systems and architectures. Based on these results, we then collaborated with the security community in a large-scale campaign to reduce the number of vulnerable NTP servers by more than 92%. To assess possible next steps of attackers, we evaluate amplification vulnerabilities in the TCP handshake and show that attackers can abuse millions of hosts to achieve 20x amplification. Lastly, we analyze the root cause for amplification attacks: networks that allow IP address spoofing. We deploy a method to identify spoofing-enabled networks from remote and reveal up to 2,692 Autonomous Systems that lack egress filtering.

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Tags: Amplification DDoS, Device Fingerprinting, Internet-wide Scanning, Measurements, TCP, UDP