Application-layer denial of service attacks: taxonomy and survey

The recent escalation of application-layer denial of service (DoS) attacks has attracted a significant interest of the security research community. Since application-layer DoS attacks usually do not manifest themselves at the network level, they avoid traditional network-layer-based detection. Therefore, the security community has focused on specialised application-layer DoS attacks detection and mitigation mechanisms. However, the deployment of reliable and efficient defence mechanisms against these attacks requires the comprehensive understanding of the existing application-layer DoS attacks supported by a unified terminology. Thus, in this paper we address this issue and devise a taxonomy of application-layer DoS attacks. By devising the proposed taxonomy, we intend to give researchers a better understanding of these attacks and provide a foundation for organising research efforts within this specific field

Denial of Service: Techniques of Attacks and Mitigation

As cloud computing technology has many advantages but cloud security or cloud software security threats and attacks at various levels are also a big concern of all the organizations. Those systems are connected to the internet in the cloud network can be effected by different types of attacks and one of the prominent attack is DoS (denial of service) attack. DoS attack has been considered as one of the important security threat in cloud computing systems at various level that has proven difficult to alleviate. This attack perpetrated in many ways such as consuming computational resources, disruption of information and obstructing the communication media. Once the attack is successful in consuming resources on the victim computers, the attacker then could control and direct them to attack as a group. This means DoS attack also allows the attacker to get the administrative control of the systems. Dos attack can be launched for sending the flood or crashes the services of the system. In this paper, we present the different types of DoS attacks and techniques for launched the DoS attack at various level and the techniques applied to mitigate the harmful effects of the DoS attack

A hybrid agent-based classification mechanism to detect denial of service attacks

This paper presents the core component of a solution based on agent technology specifically adapted for the classification of SOAP messages. The messages can carry out attacks that target the applications providing Web Services. One of the most common attacks requiring novel solutions is the denial of service attack (DoS), caused for the modifications introduced in the XML of the SOAP messages. The specifications of existing security standards do not focus on this type of attack. This article presents an advanced mechanism of classification designed in two phases incorporated within a CBR-BDI Agent type. This mechanism classifies the incoming SOAP message and blocks the malicious SOAP messages. Its main feature involves the use of decision trees, fuzzy logic rules and neural networks for filtering attacks. These techniques provide a mechanism of classification with the self-adaption ability to the changes that occur in the patterns of attack. A prototype was developed and the results obtained are presented in this study.This paper presents the core component of a solution based on agent technology specifically adapted for the classification of SOAP messages. The messages can carry out attacks that target the applications providing Web Services. One of the most common attacks requiring novel solutions is the denial of service attack (DoS), caused for the modifications introduced in the XML of the SOAP messages. The specifications of existing security standards do not focus on this type of attack. This article presents an advanced mechanism of classification designed in two phases incorporated within a CBR-BDI Agent type. This mechanism classifies the incoming SOAP message and blocks the malicious SOAP messages. Its main feature involves the use of decision trees, fuzzy logic rules and neural networks for filtering attacks. These techniques provide a mechanism of classification with the self-adaption ability to the changes that occur in the patterns of attack. A prototype was developed and the results obtained are presented in this study

A survey of denial-of-service and distributed denial of service attacks and defenses in cloud computing

Cloud Computing is a computingmodel that allows ubiquitous, convenient and on-demand access to a shared pool of highly configurable resources (e.g., networks, servers, storage, applications and services). Denial-of-Service (DoS) and Distributed Denial-of-Service (DDoS) attacks are serious threats to the Cloud services’ availability due to numerous new vulnerabilities introduced by the nature of the Cloud, such as multi-tenancy and resource sharing. In this paper, new types of DoS and DDoS attacks in Cloud Computing are explored, especially the XML-DoS and HTTP-DoS attacks, and some possible detection and mitigation techniques are examined. This survey also provides an overview of the existing defense solutions and investigates the experiments and metrics that are usually designed and used to evaluate their performance, which is helpful for the future research in the domain

S-MAS: An adaptive hierarchical distributed multi-agent architecture for blocking malicious SOAP messages within Web Services environments

During the last years the use of Web Service-based applications has notably increased. However, the security has not evolved proportionally, which makes these applications vulnerable and objective of attacks. One of the most common attacks requiring novel solutions is the denial of service attack (DoS), caused for the modifications introduced in the XML of the SOAP messages. The specifications of existing security standards do not focus on this type of attack. This article presents the S-MAS architecture as a novel adaptive approach for dealing with DoS attacks in Web Service environments, which represents an alternative to the existing centralized solutions. S-MAS proposes a distributed hierarchical multi-agent architecture that implements a classification mechanism in two phases. The main benefits of the approach are the distributed capabilities of the multi-agent systems and the self-adaption ability to the changes that occur in the patterns of attack. A prototype of the architecture was developed and the results obtained are presented in this study

Denial of Service in Web-Domains: Building Defenses Against Next-Generation Attack Behavior

The existing state-of-the-art in the field of application layer Distributed Denial of Service (DDoS) protection is generally designed, and thus effective, only for static web domains. To the best of our knowledge, our work is the first that studies the problem of application layer DDoS defense in web domains of dynamic content and organization, and for next-generation bot behaviour. In the first part of this thesis, we focus on the following research tasks: 1) we identify the main weaknesses of the existing application-layer anti-DDoS solutions as proposed in research literature and in the industry, 2) we obtain a comprehensive picture of the current-day as well as the next-generation application-layer attack behaviour and 3) we propose novel techniques, based on a multidisciplinary approach that combines offline machine learning algorithms and statistical analysis, for detection of suspicious web visitors in static web domains. Then, in the second part of the thesis, we propose and evaluate a novel anti-DDoS system that detects a broad range of application-layer DDoS attacks, both in static and dynamic web domains, through the use of advanced techniques of data mining. The key advantage of our system relative to other systems that resort to the use of challenge-response tests (such as CAPTCHAs) in combating malicious bots is that our system minimizes the number of these tests that are presented to valid human visitors while succeeding in preventing most malicious attackers from accessing the web site. The results of the experimental evaluation of the proposed system demonstrate effective detection of current and future variants of application layer DDoS attacks

Déni-de-service: Implémentation d'attaques XML-DOS et évaluation des défenses dans l'infonuagique

RÉSUMÉ L’infonuagique est un paradigme informatique dont la popularité et les usages n’ont fait que croître ces dernières années. Il doit son succès à sa grande adaptabilité et capacité de mise à l’échelle, ainsi qu’à sa facilité d’utilisation. Son but est de permettre à l’individu ou à l’entreprise d’utiliser des ressources informatiques qu’il ou elle ne possède pas physiquement, en utilisant des techniques déjà connues et éprouvées comme la virtualisation et les services web. Plusieurs modèles d’infonuagique existent, selon la fonctionnalité recherchée. Par exemple, déposer, partager et accéder depuis n’importe quel terminal un fichier sur Dropbox, et exécuter une application extrêmement gourmande en ressources sur une machine louée le temps de l’exécution sont deux exemples d’utilisation de l’infonuagique. Le modèle d’infonuagique influe sur la portion des ressources gérées par l’utilisateur, en comparaison des ressources gérées par le fournisseur. Dans le cas de Dropbox, l’utilisateur n’a pas besoin de se soucier des ressources allouées à sa requête ni de savoir quel système d’exploitation a servi ou encore comment est gérée la base de données, alors que dans l’autre cas tous ces paramètres rentreront probablement en compte et seront donc à la charge de l’utilisateur. Un réseau d’infonuagique peut tout autant être un réseau public accessible de tous moyennant finances, qu’un réseau privé bâti et utilisé seulement par une entreprise pour ses propres besoins. L’attrait considérable de l’infonuagique, pour les particuliers comme pour les entreprises, augmente par le fait même les risques liés à la sécurité de ces réseaux, ceux-ci devenant une cible de choix pour les attaquants. Ce risque accru allié à la confiance que l’utilisateur doit porter au fournisseur pour gérer et protéger ses données explique que nombreux sont ceux encore réticents à utiliser l’infonuagique, que ce soit pour des questions de confidentialité pour une entreprise ou de vie privée pour un particulier. La diversité des technologies utilisées implique une grande variété d’attaques possibles. Notamment, les réseaux d’infonuagique pâtissent des mêmes vulnérabilités que les réseaux conventionnels, mais également des failles de sécurité liées à l’utilisation de machines virtuelles. Cependant, ces menaces sont dans l’ensemble bien connues et la plupart du temps des mesures sont mises en place pour les contrer. Ce n’est pas le cas des vulnérabilités liées à l’utilisation des services web, utilisés abondamment dans le cas de l’infonuagique. Les réseaux d’infonuagique se donnent pour but d’être accessibles depuis n’importe où et n’importe quel appareil, ce qui passe nécessairement par l’utilisation de services web. Or les serveurs web sont extrêmement vulnérables aux attaques de type XML-DoS, mettant à profit des requêtes SOAP (Simple Object Access Protocol) utilisant un message XML malveillant. Ces attaques ont pour but d’utiliser une très grande partie si ce n’est pas toutes les ressources CPU et mémoire de la machine hébergeant le serveur web victime, la rendant indisponible pour des utilisateurs légitimes, ce qui est le but recherché lors d’une attaque de déni de service. Ces attaques sont extrêmement intéressantes d’un double point de vue. Elles sont tout d’abord très difficiles à détecter, car l’utilisateur qui en est à l’origine est perçu comme un utilisateur légitime (attaque au niveau de la couche application, donc impossible de la détecter au niveau de la couche TCP/IP). De plus, elles présentent une dissymétrie importante entre les ressources dont l’attaquant a besoin pour monter l’attaque, et les ressources nécessaires pour traiter la requête. En effet, une requête SOAP mal formée bien que très basique peut déjà demander des ressources considérables au serveur web victime. Ce type d’attaques ayant été assez peu étudié, malgré son efficacité et l’omniprésence des services web dans l’infonuagique, nous nous sommes proposé de démontrer et de quantifier l’impact que peuvent avoir ces attaques dans le cadre de l’infonuagique, pour ensuite proposer des solutions possibles pour s’en défendre. Nous avons jugé qu’il était plus approprié de recourir à des outils de simulation pour mener nos travaux, pour plusieurs raisons comme notamment la possibilité de suivre de façon précise l’évolution des ressources des différents serveurs du réseau, et la plus grande liberté qui nous était laissée de construire notre propre topologie. Notre première contribution est de mettre en avant les équipements vulnérables dans un réseau d’infonuagique, et les différentes façons de les attaquer, ainsi que les différents types d’attaques XML-DoS. Cette analyse nous a permis d’apporter notre deuxième contribution, qui consiste à utiliser et à modifier en profondeur un simulateur d’infonuagique (le simulateur GreenCloud, basé sur le simulateur NS2) afin de le rendre apte à l’étude des attaques XML-DoS et plus réaliste. Une fois ces changements effectués, nous montrons l’efficacité des attaques XML-DoS et les répercussions sur les usagers légitimes. Par ailleurs, nous réalisons une comparaison critique des principales défenses contre les attaques XML-DoS et contre les services web en général, et sélectionnons celle qui nous semble la plus pertinente, afin de la mettre à l’épreuve de la simulation et de mesurer son efficacité. Cette efficacité doit être démontrée aussi bien en terme de capacité à déjouer l’attaque menée à l’étape précédente, que de précision en terme de "false positives" et "false negatives". Un des défis majeurs consiste en effet à concilier une défense qui se veut universelle pour toutes les machines du réseau, tout en étant capable de s’adapter à la grande hétérogénéité des services web qui cohabitent au sein d’un réseau d’infonuagique. Ces expérimentations sont alors l’objet de discussions et de conclusions sur la position à adopter quant aux attaques XML-DoS dans les réseaux d’infonuagique, notamment les défenses à adopter et les pratiques à observer, la défense choisie à l’étape précédente ayant montré quelques limitations. Nous sommes partis de l’hypothèse que chacun des modèles d’infonuagique pouvait être touché par ce type d’attaques, bien que de façons différentes. Quel que soit le modèle d’infonuagique, il peut en effet avoir recours à des services web et se retrouve donc vulnérable d’une façon ou d’une autre, qu’il s’agisse d’un serveur web gérant toutes les requêtes entrantes des utilisateurs, ou un serveur web qu’un utilisateur a lui-même installé sur une machine virtuelle qu’il loue au fournisseur. Nous avons aussi jugé essentiel d’introduire les spécificités liées à l’utilisation de machines virtuelles, comme la compétition pour les ressources entre machines virtuelles situées sur une même machine physique.----------ABSTRACT Cloud Computing is a computing paradigm that has emerged in the past few years as a very promising way of using highly scalable and adaptable computing resources, as well as accessing them from anywhere in the world and from any terminal (mobile phone, tablet, laptop...). It allows companies or individuals to use computing infrastructures without having to physically own them, and without the burden of maintenance, installations, or updates. To achieve that, Cloud Computing uses already known and tested technologies such as virtualization and web services. Several Cloud Computing models exist, divided by how much of the infrastructure the user is in charge of, ranking from nothing at all (the provider is in charge of everything, from the operating system to the applications installed) to managing a whole virtual machine without even an operating system preinstalled. For instance, sharing and accessing a document on Dropbox, or running a resource intensive application on a rented machine, are both exemples of what can be done with Cloud Computing. In the case of Dropbox, the user doesn’t care what resources are allocated for his requests, no more than he needs to know on what operating system the request was run or how the database was accessed. But all those aspects will be part of what the user has to know and adjust in the second case. A Cloud Computing network can be public, as it is the case for Amazon, which allows you to access its resources if you pay for it, or private, if a company decides to build a cluster for its own needs. The strong appeal of Cloud Computing, for both businesses and individuals, dramatically increases the security risks, because it becomes a key target for attackers. This increased risk, added to the confidence the users must have in their services provider when it comes to managing and protecting their data, may explain why many are still reluctant to take the leap to Cloud Computing. For instance, a company may be reluctant for confidentiality reasons, while individuals may hesitate for privacy concerns. The broad range of technologies used in Cloud Computing makes it at risk for a wide variety of attacks, since it already comes with all the vulnerabilities associated with any conventional network, and all the security breaches that affect virtual machines. However, those threats are usually well documented and easily prevented. But this is not the case of the vulnerabilities that come from the use of web services, that are heavily used in Cloud Computing. Cloud Computing networks aim at being accessible from all over the world and on almost any device, and that implies using web services. Yet, web services are extremely vulnerable to XML-DoS type of attack. Those attacks take advantage of Simple Object Access Protocol (SOAP) requests using a malicious XML content. Those requests can easily deplete a web server from its resources, be it CPU or memory, making it unavailable for legitimate users; this is exactly the goal of a denial-of-service attack. The XML-DoS attacks are extremely interesting in two ways. First, they are very hard to detect, since the attack takes place on the application layer, so the user appears to be legitimate (it’s impossible to detect it on the TCP/IP layer). Second, the resources needed to mount the attack are very low compared to what is needed on the web server side to process even a basic but malformed request. This type of attack has been surprisingly left quite aside, despite its efficiency and the omnipresence of web services in Cloud Computing networks. This is the reason why we decided to prove and quantify the impact such attacks can have on Cloud Computing networks, to later propose possible solutions and defenses. We estimated that using a simulated environment was the best option for various reasons, like the possibility to monitor the resources of all the servers in the network, and the greater freedom we had to build our own topology. Our first contribution is to emphasize the vulnerable equipments in a Cloud Computing network, and the various ways to attack them, as well as the various forms an XML-DoS attack can take. Our second contribution is then to use, modify and improve a Cloud Computing simulator (the GreenCloud simulator, based on NS2), in order to make the study of XML-DoS attacks possible. Once the changes are made, we show the efficiency of XML- DoS attacks, and the impact they have on legitimate users. In addition, we compare the main existing defenses against XML-DoS attacks and web services attacks in general, and pick the one that seems to be best suited to protect Cloud Computing networks. We then put this defense to the test in our simulator, to evaluate its efficiency. This evaluation must take into consideration not only the ability to mitigate the attack we led in the previous step, but also the number of false positives and false negatives. One of the major challenges is to have a defense that will conciliate the ability to protect all the machines in the network, while still being able to adapt to the great heterogeneity of the various web services hosted at the same time in a Cloud Computing network. Those experimentations are then subjected to discussions and conclusions on the decisions to take when it comes to XML-DoS attacks. In particular, what defenses should be adopted and what practices should be followed, because the evaluation of the defense at the previous step will show that it may not be the optimal solution; this will be our final contribution. We made the assumption that all the Cloud Computing models could be the target of a XML-DoS attack in some way. No matter the model, it can actually use web services and is then vulnerable to those attacks, whether it is a web server handling incoming requests for all the users, or a web server a user installed on the virtual machine he rents. We thought it was essential to take into consideration the specificity of virtual machines, such as the contention for resources when they are located on the same physical machine

Automated and Effective Security Testing for XML-based Vulnerabilities

Nowadays, the External Markup Language (XML) is the most commonly used technology in web services for enabling service providers and consumers to exchange data. XML is also widely used to store data and configuration files that control the operation of software systems. Nevertheless, XML suffers from several well-known vulnerabilities such as XML Injections (XMLi). Any exploitation of these vulnerabilities might cause serious and undesirable consequences, e.g., denial of service and accessing or modifying highly-confidential data. Fuzz testing techniques have been investigated in the literature to detect XMLi vulnerabilities. However, their success rate tends to be very low since they cannot generate complex test inputs required for the detection of these vulnerabilities. Furthermore, these approaches are not effective for real-world complex XML-based enterprise systems, which are composed of several components including front-end web applications, XML gateway/firewall, and back-end web services. In this dissertation, we propose several automated security testing strategies for detecting XML-based vulnerabilities. In particular, we tackle the challenges of security testing in an industrial context. Our proposed strategies, target various and complementary aspects of security testing for XML-based systems, e.g., test case generation for XML gateway/firewall. The development and evaluation of these strategies have been done in close collaboration with a leading financial service provider in Luxembourg/Switzerland, namely SIX Payment Services (formerly known as CETREL S.A.). SIX Payment Services processes several thousand financial transactions daily, providing a range of financial services, e.g., online payments, issuing of credit and debit cards. The main research contributions of this dissertation are: -A large-scale and systematic experimental assessment for detecting vulnerabilities in numerous widely-used XML parsers and the underlying systems using them. In particular, we targeted two common XML parser’s vulnerabilities: (i) XML Billion Laughs (BIL), and (ii) XML External Entities (XXE). - A novel automated testing approach, that is based on constraint-solving and input mutation techniques, to detect XMLi vulnerabilities in XML gateway/firewall and back-end web services. - A black-box search-based testing approach to detect XMLi vulnerabilities in front-end web applications. Genetic algorithms are used to search for inputs that can manipulate the application to generate malicious XML messages. - An in-depth analysis of various search algorithms and fitness functions, to improve the search-based testing approach for front-end web applications. - Extensive evaluations of our proposed testing strategies on numerous real-world industrial web services, XML gateway/firewall, and web applications as well as several open-source systems