Faculty Publications
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Item Multiplexed Asymmetric Attacks: Next-Generation DDoS on HTTP/2 Servers(Institute of Electrical and Electronics Engineers Inc., 2020) Praseed, A.; Santhi Thilagam, P.Distributed Denial of Service (DDoS) attacks using the HTTP protocol have started gaining popularity in recent years. A recent trend in this direction has been the use of computationally expensive requests to launch attacks. These attacks, called Asymmetric Workload attacks can bring down servers using limited resources, and are extremely difficult to detect. The introduction of HTTP/2 has been welcomed by developers because it improves user experience and efficiency. This was made possible by the ability to transport HTTP requests and their associated inline resources simultaneously by using Multiplexing and Server Push. However multiplexing has made request traffic bursty and rendered DDoS detection mechanisms based on connection limiting obsolete. Contrary to its intention, multiplexing can also be misused to launch sophisticated DDoS attacks using multiple high workload requests in a single TCP connection. However, sufficient research has not been done in this area. Existing research demonstrates that the HTTP/2 protocol allows users to launch DDoS attacks easily, but does not focus on whether an HTTP/2 server can handle DDoS attacks more efficiently or not. Also, sufficient research has not been done on the possibility of Multiplexing and Server Push being misused. In this work, we analyse the performance of an HTTP/2 server compared to an HTTP/1.1 server under an Asymmetric DDoS attack for the same load. We propose a new DDoS attack vector called a Multiplexed Asymmetric DDoS attack, which uses multiplexing in a different way than intended. We show that such an attack can bring down a server with just a few attacking clients. We also show that a Multiplexed Asymmetric Attack on a server with Server Push enabled can trigger an egress network layer flood in addition to an application layer attack. © 2005-2012 IEEE.Item Modelling Behavioural Dynamics for Asymmetric Application Layer DDoS Detection(Institute of Electrical and Electronics Engineers Inc., 2021) Praseed, A.; Santhi Thilagam, P.S.Asymmetric application layer DDoS attacks using computationally intensive HTTP requests are an extremely dangerous class of attacks capable of taking down web servers with relatively few attacking connections. These attacks consume limited network bandwidth and are similar to legitimate traffic, which makes their detection difficult. Existing detection mechanisms for these attacks use indirect representations of actual user behaviour and complex modelling techniques, which leads to a higher false positive rate (FPR) and longer detection time, which makes them unsuitable for real time use. There is a need for simple, efficient and adaptable detection mechanisms for asymmetric DDoS attacks. In this work, an attempt is made to model the actual behavioural dynamics of legitimate users using a simple annotated Probabilistic Timed Automata (PTA) along with a suspicion scoring mechanism for differentiating between legitimate and malicious users. This allows the detection mechanism to be extremely fast and have a low FPR. In addition, the model can incrementally learn from run-time traces, which makes it adaptable and reduces the FPR further. Experiments on public datasets reveal that our proposed approach has a high detection rate and low FPR and adds negligible overhead to the web server, which makes it ideal for real time use. © 2020 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See https://www.ieee.org/publications/rights/index.html for more information.Item Fuzzy Request Set Modelling for Detecting Multiplexed Asymmetric DDoS Attacks on HTTP/2 servers(Elsevier Ltd, 2021) Praseed, A.; Santhi Thilagam, P.S.The introduction of HTTP/2 has led to a dramatic change in web traffic. The steady flow of requests in HTTP/1.1 has been replaced by bursts of multiple requests, largely due to the introduction of multiplexing in HTTP/2 which allows users to send multiple requests through a single connection. This feature was introduced in order to reduce the page loading time by multiplexing a web page and its associated resources in a single connection. While this feature has significantly improved user experience, it can be misused to launch sophisticated application layer DDoS attacks against HTTP/2 servers. Instead of the intended use of multiplexing, attackers can force the web server to process multiple random requests simultaneously, leading to increased server usage. The use of computationally intensive requests can further exacerbate the situation. These attacks, called Multiplexed Asymmetric Attacks, pose a dangerous threat to HTTP/2 servers and stem from the lack of verification of the multiplexed requests. In this work, an approach to model an HTTP/2 request set as a fuzzy multiset is presented. The proposed approach uses a combination of relative cardinality and request workload to detect multiplexed AL-DDoS attacks. Experiments on open source datasets demonstrate that the proposed approach is able to detect multiplexed AL-DDoS attacks with an accuracy of around 95%, while maintaining a low False Positive Rate (FPR) of around 3%. © 2021 Elsevier LtdItem HTTP request pattern based signatures for early application layer DDoS detection: A firewall agnostic approach(Elsevier Ltd, 2022) Praseed, A.; Santhi Thilagam, P.S.Application Layer DDoS (AL-DDoS) attacks are an extremely dangerous variety of DDoS attacks that started becoming popular recently. They are executed using very few legitimate requests, making them very difficult to detect. Since they are executed using attack generation tools and botnets, AL-DDoS attacks display similarity within a request stream (temporal similarity) and across request streams (spatial similarity). Once a particular request stream has been detected as malicious by an anomaly detection mechanism (ADM), spatial similarity can help in detecting AL-DDoS attacks much earlier by employing a dynamic signature based approach. In this work, we use HTTP request patterns as signatures to build a firewall agnostic Early Detection Module (EDM) for AL-DDoS attacks. We also propose the use of Sample Entropy instead of the popular Shannon's Entropy to identify AL-DDoS attacks. Sample Entropy is able to model both the frequencies and sequence of data items within a request stream, and is a better indicator of temporal similarity than Shannon's Entropy. In this work, we demonstrate that Sample Entropy can be used effectively to detect AL-DDoS attacks. With a Sample Entropy based anomaly detection mechanism, we demonstrate that the use of EDM significantly reduces the detection latency for AL-DDoS attacks. © 2022 Elsevier Ltd