Amplification and Drdos Attack Defense – a Survey and New Perspectives
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Amplification and DRDoS Attack Defense – A Survey and New Perspectives Fabrice J. Ryba∗, Matthew Orlinski∗, Matthias Wahlisch¨ ∗, Christian Rossowy, Thomas C. Schmidtz ∗ Freie Universitat¨ Berlin, Berlin, Germany, Email: ffabrice.ryba, m.orlinski, [email protected] y Saarland University, Saarbruecken, Germany, Email: [email protected] z HAW Hamburg, Hamburg, Germany, Email: [email protected] Abstract—The severity of amplification attacks has attacks, e.g., Slowloris [21] or TCP SYN floods [22], grown in recent years with recent attacks involving several unless their defenses are also applicable to amplification hundreds of Gbps attack volume. In this paper, we survey attacks. Generally, the adversary in amplification attacks the threat of amplification attacks and compare a wide targets vulnerabilities in Internet protocols and services selection of different proposals for preventing, detecting, to amplify the amount of attack traffic. The ease of per- and filtering amplification attack traffic. Since source IP spoofing plays an important part in almost all of the forming amplification attacks and greater understanding amplification attacks surveyed, we also survey state-of- of their effect has led to an increase of attacks in recent the-art of spoofing defenses as well as approaches to trace years. This is supported, e.g., by the OpenDNS Security spoofing sources. This work acts as an introduction into Lab that saw over 5,000 different amplification attacks many different types of amplification attacks and source every hour in 2014 [23], and by Rossow’s survey of IP address spoofing. By combining previous works into a amplification vulnerabilities [13]. single comprehensive discussion we hope to prevent redun- The most prominent form of amplification attack seen dant work and encourage others to find practical solutions in recent years abuses the lack of endpoint verification for defending against future amplification attacks. in the Internet Protocol (IP) in order to trick third-party servers into sending large amounts of data to victims. I. INTRODUCTION That is, attackers spoof source IP addresses [24] to hide Denial of Service (DoS) attacks against networks at- their identity and cause third-parties to send data to the tempt to make a system or an entire network unavailable victim as identified by the source address field of the IP for its intended purpose [1]. In some cases DoS attacks packet. This is also sometimes called reflection because cause a complete loss of Internet connectivity for the attackers “reflect” attack traffic off of benign services. victim [2]. The motivation for DoS attacks can be finan- As well as reflection, attackers sometimes strive to cial [3], [4], political [2], ideological [5], reputation [6], maximize the attack bandwidth sent to the victim by arXiv:1505.07892v3 [cs.NI] 17 May 2016 [7], to test new techniques and prepare for larger attacks, using amplification. For example, many UDP-based pro- or purely for disruptive purposes [8]. tocols (such as DNS or NTP) that have a higher response A general overview of DoS attacks and defense strate- payload size than the requests can be abused to amplify gies can already be found in the surveys by Mirkovic the reflected attack traffic. Consider DNS, while DNS and Reiher [9], Douligeris and Mitrokotsa [10], and lookup requests are typically rather small, the responses more recently Zargar et al. [11]. Instead, this paper may be significantly larger, e.g., due to verbose informa- focuses on a particular type of DoS attack called an tion such as DNSSEC records. amplification attack (also called Distributed Reflective By combining reflection and amplification attackers Denial of Service (DRDoS) attacks [12], [13]) where the can generate attack traffic volumes which are signifi- attacker seeks to maximise the volume of attack traffic cantly higher than their uplink bandwidth [2], [4], [8], sent to the victim whilst minimising the volume of traffic [25]. Furthermore, not only single hosts may be affected they send to trigger the attack [14]–[20]. We will not by such attacks. Entire networks may struggle to cope discuss other low traffic volume and high impact DoS with the extra bandwidth and processing demands [25]. Section 1: Introduction from the past and discuss amplification attacks in great Section 2: Reflection and Amplification Attacks detail. We then describe methods to prevent amplification Previous Attacks Attack Models attacks in Section III. Then special attention is paid to Section 3: Preventing Amplification Attacks preventing reflection and IP spoofing in Section IV. We Alternative Architectures Lowering Amplification Factors Reducing Number of Amplifiers Response Rate Limiting UDP Sessions Filtering Spoofed Packets finish the discussion about the solution space in Sec- tion V by presenting approaches to detect and filter am- Section 4: Source IP Address Spoofing plification attacks. Finally, we conclude in Section VI. Monitoring Spoofing In The Wild Active Monitoring Passive Monitoring II. AMPLIFICATION ATTACKS Detecting and Filtering Spoofed Packets Flow Correlation This section provides a detailed introduction into the Validating Source Address Using Network Knowledge End-to-end IP Headers, e.g., TTL different techniques for amplifying attack traffic. We start Encryption Ingress and Egress Filtering Third-party Authentication Learning Flow Directions by giving a brief taxonomy and timeline of different Routing Tables types of amplificaiton attacks, and then we end the section by describing the techniques used in more detail. Tracing Spoofing Attacks Traffic Logs Packet Marking ICMP Traceback Link Testing Section 5: Detecting Amplification Attacks and Filtering Attack Traffic A. Taxonomy and Historical Background Locations for Detecting and Filtering Attack Traffic There are many ways of amplifying the volume of Victim-end Source-end Reflectors/Amplifiers Distributed attack traffic in DoS attacks. In this paper we give Predicting Future Attacks special focus to amplification attacks which use UDP Game Therory Scan Detection based amplifying protocols and reflection. However, it is Section 6: Conclusions, ongoing projects, and future work important to be able to distinguist between the different types of amplificaiton attacks. Fig. 1. Categorisation of the amplification DDoS literature. 1) DNS Servers as Amplifiers: In 1999, AusCERT [27] warned about amplification attacks where attackers trick DNS servers into sending large Defending against this form of amplification attack amounts of data to spoofed IP addresses [24]. In 2000, is challenging for network operators. Firstly, the attack the CIAC warned of Distributed Denial of Service traffic blends in benign communication and may be (DDoS) attacks where attackers can send spoofed IP hard to distinguish from legitimate traffic. Secondly, packets from many different locations [28]. the attack packets received by victims are reflected by Today, DNS is widely used in amplification attacks many distributed benign third-parties such as open DNS because a 60 byte request from an attacker can easily resolvers, effectively hiding the attacker’s identity [26]. generate a 512 byte response [2], [8], [14]. Furthermore, In this survey paper, we systematically structure ex- DNS servers which support Extension mechanisms for isting research on amplification attacks to assist future DNS (EDNS) [29] can generate responses which are research in this direction. To the best of our knowledge, nearly 100 times larger than requests [13]. Some at- we are the first to categorize an research area that spans tackers even ensure large responses by creating domains almost 200 publications and has become an important specifically to use in amplification attacks [23]. problem both in academia and practice. To this end, we Any public DNS server which is configured to respond first compare various definitions and types of amplifica- to requests for hosts outside of their domain can be used tion attacks. With this foundation, we then systematize in amplification attacks. DNS servers that are configured preventive countermeasures, and particularly look at the to respond to all such requests are known as open DNS problem of (identifying and mitigating) IP spoofing. We resolvers. According to the Open DNS Resolver Project complete our survey with works that proposed reactive approximately 25 million open DNS resolvers currently countermeasures to defend against ongoing amplification “pose a significant threat” to the Internet [26]. It is also attacks. Our main contribution is thus a comprehensive not difficult to find enough open DNS resolvers to use survey of existing literature that until now was scattered. in amplification attacks. Rossow showed that it currently The rest of this paper is organised as shown in only takes 90 seconds to acquire a list of 100,000 open Figure 1. In Section II, we present prominent incidents DNS resolvers [13]. 2 400 300 167 SNMP attack at MIT and100 SSDP attack Vaughn and Evron present DNS 54 AusCERT warns about DNS DNS is regularly used in DERP claims responsibility for many Estimated attack traffic (Gbps) amplification attacks Akamai reports a 54Gbps based amplification attacks 300Gbps DNS attack against SpamHaus 100Gbps DNS attack against GreenNet CloudFlare reports a 400Gbps NTP attack Amplification Attacks at DEFCON 14 Prolexic reports a 167Gbps DNS attack attacks against the gaming industry 1998 2001 2004 2007 2013 F eb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 2014 F eb Mar Oct Fig. 2. Timeline of amplification attacks and related events. 2) Other UDP Based Services: The DNS based broadcast may be amplifiers as well. For example, in amplification attacks just described use source IP ad- Fraggle attacks an attacker may send CharGen requests dress spoofing to trick third-parties into attacking a to the broadcast address of many networks at the same victim [24]. time [37]. End hosts which receive CharGen requests Source IP address spoofing also makes it very difficult may respond with much more data than they receive, for the victim to track attacker because all attack traffic thus the end hosts in Fraggle attacks are amplifiers as they receive will come from third-parties.