=Paper=
{{Paper
|id=Vol-3200/paper6
|storemode=property
|title=Detection of Slow DDoS Attacks Based on Time Delay Forecasting
|pdfUrl=https://ceur-ws.org/Vol-3200/paper6.pdf
|volume=Vol-3200
|authors=Vitalii Savchenko,Valeriia Savchenko,Oleksandr Laptiev,Oleksander Matsko,Ivan Havryliuk,Kseniia Yerhidzei,Iryna Novikova
}}
==Detection of Slow DDoS Attacks Based on Time Delay Forecasting ==
Detection of Slow DDoS Attacks Based on Time Delay Forecasting Vitalii Savchenko1, Valeriia Savchenko2, Oleksandr Laptiev3, Oleksander Matsko4, Ivan Havryliuk5, Kseniia Yerhidzei6 and Iryna Novikova7 1,2 State University of Telecommunications, Solomianska str.7, Kyiv, 03110, Ukraine 3 Taras Shevchenko National University of Kyiv, 24 Bogdana Gavrilishina str., Kyiv, 04116,Ukraine, 4,5,6,7 The National Defense University of Ukraine named after Ivan Cherniakhovskyi, Povitroflotsky av. 28, Kyiv, 03049, Ukraine Abstract The article deals with the problem of detecting low and slow distributed DDoS attacks. Detecting such DDoS attacks is challenging because slow attacks do not significantly increase traffic. The authors suggest that detecting slow DDoS attacks will be effective based on analyzing and predicting host response latency in the network. The article proposes an original method for detecting such attacks, based on statistics of host interaction and predicting the individual trajectory of the traffic parameter behavior. The host response time delay is taken as a traffic parameter. An algorithm for calculating the individual trajectory of the time delay is proposed. The possibilities of using this method are shown based on the simulation of RUDY attacks on HTTP services. The parameters of the forecast accuracy are investigated depending on the accumulated information on the response delays. Keywords 1 Slow and low DDoS attacks, slow attack detection, network response prediction, latency, individual trajectory. 1. Introduction filling. The attacker opens many endless connections and, when a certain threshold is exceeded, causes a denial of service in the victim's Recently, DDoS attacks are rapidly increasing network. It uses transport (TCP) or application in scale, frequency and technical complexity. For (HTTP) protocols. Detection and organizations that rely on Internet resources and countermeasures must be built based on the applications for their activities (for example, for characteristics of the attack. e-commerce enterprises), the consequences of Countering such attacks should include two DDoS attacks can be devastating. Inaccessible main measures: 1) diagnose the attack at the websites and servers can cast a shadow on a earliest stages; 2) separate malicious traffic from company's reputation and customers turn to normal traffic. By understanding which user competitors' resources [1]. requests are the result of a DDoS attack, you can One type of DDOS attack is slow denial of configure appropriate settings for firewalls, service attacks. Their feature is that denial of routers, or implement other security measures. service is achieved in a hidden way using a small amount of traffic and does not require bandwidth III International Scientific And Practical Conference “Information Security And Information Technologies”, September 13–19, 2021, Odesa, Ukraine EMAIL: savitan@ukr.net (A. 1); savchenko.valeriya@gmail.com (A. 2); alaptev64@ukr.net (A. 3); macko2006@ukr.net (A. 4); ivan.havryliuk@gmail.com (A. 5); ergidzey@ukr.net (A. 6); irina_nov@ukr.net (A. 7) ORCID: 0000-0002-3014-131X (А.1); 0000-0003-1921- 2698 (A. 2); 0000-0002-4194-402X (A. 3); 0000-0003-3415- 3358 (A. 4); 0000-0002-3514-0738 (A. 5); 0000-0003-4634-133X (A. 6); 0000-0003-4854-0682( A. 7) ©️ 2021 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0). CEUR Workshop Proceedings (CEUR-WS.org) 1.1. Problem Statement characteristics of malicious TCP streams by classifying them by decision trees. The studies are conducted using a combination of two datasets, Methods for detecting slow DDoS attacks fall one generated from a simulated network and the into two categories: other from a publicly available CIC DoS dataset. 1. Signature methods, which are based on the Since this approach includes elements of artificial construction of a model of "abnormal behavior" intelligence, a significant amount of statistics is [2]. This model builds signatures of "abnormal" required to train the system. traffic behavior (a huge number of simultaneously In [5], the authors tried to measure the impact arriving SYN + ACK packets, an inadequately of different variants of pulsating distributed long packet lifetime, too long a packet route denial-of-service attacks on the self-similar nature "length", and so on). The model is most effective of network traffic and see if changing the H index against attacks that fill the network bandwidth, or can be used to distinguish them from a normal on local networks, where you can make a list of network. This approach is quite effective in the source addresses whose packets are guaranteed to case of traffic self-similarity elements. Otherwise, be "normal". But such a model is ineffective detecting low and slow DoS attacks is very against low-intensity DDoS, when it is difficult to difficult. reliably distinguish ordinary user requests from Paper [6] proposes Canopy, a novel approach “malicious” ones. to detecting LSDDoS attacks by using machine 2. Based on anomalies. This method is the learning techniques to extract meaning from opposite of signature. A general model of observed TCP state transition patterns. At the "normal" behavior is built, then the incoming same time, as in other models based on artificial traffic is compared with it, and if the differences intelligence, the detection system requires a large exceed an acceptable threshold, an "alarm" is sample of training and significant resources for triggered. Research is conducted in the areas of processing the results. statistical (parametric and nonparametric) The work [7] compares machine learning methods, as well as data mining and neural methods for recognizing slow DDoS attacks: networks. The last two approaches are being multilayer perceptron (MLP), backpropagation actively developed to detect low-intensity attacks. neural network, K-Nearest Neighbors (K-NN), Disadvantages of the model: a large number of Support Vector Machine (SVM) and polynomial errors of the first kind due to the individuality of naive Bayesian (MNB) algorithm. As in the networks and traffic; long-term calculation of data previous cases, the application of the methods on "normal" behavior; sensitive to the choice of requires a large number of patterns for statistical distributions. recognition. In any case, the problem of early detection of In [8-9], a new classification method and low or slow DDoS attacks remains relevant. The model is proposed to protect against slow HTTP sooner the traffic parameters are found to be attacks in the cloud. The solution detects slow inconsistent with their normal values, the faster it HTTP header attacks (Slowloris), slow HTTP will be possible to take measures to neutralize the body attacks (RUDY), or slow HTTP read attacks. attack. In this case, it is necessary to add At the same time, such approaches do not parameter prediction modules to the existing guarantee effective detection of attacks at the detection systems. early stages of their development. The papers [10-11] show a system that can 1.2. Related Works Overview detect and mitigate attacks in the network infrastructure. The main identification parameters There is a huge number of publications on the in both models are the packet transmission rate detection of slow DDoS attacks. and the uniform distance between packets, which Reference [3] proposes an architecture that does not allow to forestall the actions of intruders. mitigates low and slow DDoS attacks by Reference [12] discusses sampling data to create leveraging the capabilities of a software-defined different class distributions to counteract the infrastructure. At the same time, this approach effects of highly imbalanced slow HTTP DoS requires a significant amount of computing datasets. At the same time, a significant number resources, which will be involved in diagnostics. of samples (the authors use 1.89 million copies of The article [4] proposes a methodology for attacks) in reality is quite difficult to achieve. The detecting LDDoS attacks based on the study [13] developed a metric-based system for detecting traditional slow attacks, which can be The most expedient for detecting slow DDoS effective with limited resources, based on the attacks is the architecture proposed in [18]. Such study of similarities and the introduction of the an IDS should consist of four modules: 1) traffic Euclidean metric. This approach is only effective collection module; 2) module for calculating enough for a large number of such slow attack traffic parameters; 3) forecasting module; 4) patterns, and for a large variety of such an module for classifying attacks (Fig. 1). approach is unlikely to be effective. The system works as follows: The most practical for implementation is the 1. For some time, the Traffic Collection method proposed in [14,26], which determines the Module records the main traffic parameters quality parameters of TCP connections, typical required for further calculations: IP addresses of for slow HTTP attacks. This allows you to the sender and recipient; TCP window size; estimate the likelihood and time of the web server package arrival time. going into overload mode. However, such attack detection is based on observation statistics and uses predictions. The article [15] proposes an Traffic Collection Module algorithm for detecting slow DDoS attacks based on traffic patterns depending on the server load state. This does not consider the decision-making Traffic Parameters Calculation process. In [16], various scenarios are considered Module and a hybrid neural network for detecting DDoS attacks is proposed. However, the method and Forecasting Module general technique for detecting low intensity DDoS attacks are not considered. In [17], the authors consider interval forecasting based on a probabilistic neural network with a dynamic Attack Classification Module update of the smoothing parameter. But the problem of the dynamics of the model remains Figure 1: IDS structure unresolved. Thus, most of the works devoted to countering 2. In the module for calculating traffic slow DDoS attacks are based on statistical parameters for each IP address, the average delay models, do not address the issues of predicting between transmitted packets is calculated host behavior, and therefore are not effective enough to detect attacks at early stages. 1 k The aim of this work is to form a system for T= ( ti +1 − ti ) k − 1 i =1 (1) detecting slow DDoS attacks based on predicting traffic elements in the network. To successfully where: solve the identified problem, it is necessary to t i – the i-th package arrival time; build a model and technology for predicting the ti +1 – the i+1-th package arrival time; behavior of traffic parameters taking into account k – the number of packets received during the the history of host interaction in the network, as analyzed period. well as to propose a technology for recognizing The beginning and end of the session are recorded slow DDoS attacks. by a built-in timer, after which the duration of open connections is calculated. 2. Development of a method for 3. The decision on the presence of a possible detecting slow DDOS attacks slow HTTP attack is made in the attack classification module based on the comparison of based on predicting of traffic the obtained indicators with the average statistical parameters values. 2.1. Determining the traffic As it was shown in [18] the decision about the presence of a slow DDoS attack should be made parameter for detecting a slow based on the traffic parameters forecast, which DDoS attack can be generated based on the study of statistics in other systems. Thus, it is advisable to add a situation forecast block to the considered action of a specific implementation x ( t ) beyond the algorithm. limits S0 based on the definition of a posteriori process X ( t ) [23]. 2.2. Predicting the delay time The probability that a particular trajectory of a between transmitted packets parameter guaranteed to fall within the acceptable range s tk , if by then tk including his The interaction of computer systems in the network forms an individual trajectory of changes condition was described as x ( t ) ,t1 t tk [24], in traffic parameters for each pair of interaction. will be Such trajectories have their own characteristics P ps ( s ) = P X ( s ) S0 x ( t ) , both in the normal mode of operation and during (2) t1 t tk ,s tk a slow DDoS attack. In order to start actions on time to neutralize a slow DDoS attack, it is To solve the forecasting problem, the process necessary to predict the time trajectory of traffic under study must be represented by the formula parameters, which depends on the actions of the X ( t ) = m ( t ) + V ( t ) , (3) interacting system. Prediction of an individual traffic trajectory where m ( t ) – mean function of the process; has already been studied in [19], in which traffic ( t ) – non-random (coordinate) time parameters were determined at long intervals (week, month). The same approach was used to functions; predict slow DDoS attacks in [18]. At the same V – random, uncorrelated coefficients time, in both cases, only direct indicators were M V = 0 , M V ,V = 0 , v . investigated: in [19] - the amount of information This representation, proposed in [18, 19], per unit of time, in [18] - the average delay between transmitted packets. allows it to be applied to any traffic parameter that Slow DDoS attacks are characterized by the can be represented as a time series. Process X ( t ) fact that they are not characterized by significant can be written as a random sequence deviations in traffic indicators and therefore X ( ti ) = X ( i ) ,i = 1,I in a discrete series of different parameters must be used to detect them. Along with direct indicators (the amount of observations ti [25]: information and the average delay time), when i X ( i ) = m ( i ) + Vvv ( i ),i = 1,I , (4) using the method of canonical decomposition of a v =1 random process, the values of the correlation where V – random coefficient with parameters function are also calculated for each of the measurements, which makes the method more M V = 0 , M V ,V = 0 , v ; M Vv2 = Dv ; effective for predicting weak disturbances. To monitor the traffic parameters, as before in ( i ) – non-random coordinate function, [18], it is advisable to use the average time v ( v ) = 1 , v ( i ) = 0 while v i . interval of the delay between packets in the The formulas for variance and correlation session, which can be represented as a vector of function can be written as parameters X = ( X1 , X 2 ,..., X H ) [20]. Condition i D ( i ) = Dvv2 ( i ) ,i = 1,I , (5) fulfillment X S0 , where S0 this is the tolerance v =1 area of the vector X. Random process X ( t ) inf ( i, j ) D ( i, j ) = Dvv ( i )v ( j ) , i, j = 1,I . (6) reflects the change in delays between traffic v =1 packets over time [21]. Process X ( t ) statistically Thus, the representation of random processes defined in the range t t1 , where t1 is the of traffic parameters (2) allows solving the beginning of observations and tk t1 [22]. problem of detecting a slow DDoS attack based on predicting the delay between transmitted The forecasting problem is posed as follows: packets. for the parameter x ( t ) S0 , which is observed in the interval t1 t tk , determine the release time 2.3. Slow DDoS Attack detection 22. For i = 2 to i T 23. For l = 1 to l = L algorithm based on delay time i −1 prediction 24. Vl ,i = Xˆ l ,i − Vl ,k k ,i ‒ determination of k =1 To detect slow DDoS attacks within the random coefficients. framework of approach (1) - (6), the following 25. for l algorithm for predicting delays between 26. for i transmitted packets is proposed. 27. ps Length x ( ) ‒ size of the array of 0. Start control results. 1. X ( t ) X ( t ) ,t = 1,T ‒ formation of an array of 28. M1 = Table mi + ( x1 − m1 ) 1,i , i = 1,T ‒ process observations X ( t ) . determination of the initial predicted 2. x ( ) x ( ) , = 1,k ‒ formation of an array of trajectory. control results. 29. For h = 2 to h = ps 3. L Length X ( t ) ‒ determining the number M h−1,i + ( xh − M h−1,h ) h,i , 30. M h = Table ‒ of trajectories observed. 4. m (t ) = Mean X (t ) ‒ calculating the mean of a i = 1,T calculation of forecast control points. random function X ( t ) . 31. for h 5. c = Covariance X (t ) ‒ calculating the i M k ,i + Vk , jk , j , covariance matrix for X ( t ) . 32. X forecast = Table j = k +1 ‒ 6. d = Variance X (t ) ‒ calculating an array of k = 1, ps ,i = 1,T variances of a process X ( t ) . calculation of predicted trajectory. 7. = Table 0,T ,T ‒ determining the initial 33. End value of the coordinate functions. 8. X̂ ( t ) = X ( t ) − m ( t ) ,t = 1,T ‒ centering the source The application of the algorithm makes it possible to construct a forecast of the system response data. delay time and determine the moment when this 9. V ( t ) = X l ( t ) − m ( t ) ,t = 1,T ; l = 1,L ‒ parameter goes beyond the critical values. In the determination of initial values of random event that latency is classified as a slow DDoS coefficients. attack, security measures must be taken. A slow c DDoS attack decision must be made for each 10. 1 = 1, j , j = 1,T ‒ definition of the first sender IP address based on a comparison of d1 predicted latency parameters with critical values coordinate function. to determine when the parameter enters the 11. For i = 1 to i = T critical zone. This approach takes into account the i −1 12. di = ci,i − i,2 j d j ‒ variance override. statistics of the behavior of the interacting hosts, j =1 as well as the behavior of other hosts in similar 13. For j = 1 to j = T situations in the event of a slow DDoS attack. 1 i −1 14. i = ci, j − dl i,l j ,l ‒ redefining 3. Application of the algorithm for d1 l =1 coordinate functions. detecting slow DDOS attacks 15. for j based on predicting the response 16. for i delay time 17. For i = 2 to i T 18. For k = 1 to k i Slow DDOS attack detection simulations are 19. i,k = 0 ‒ redefining the coordinate performed for the RUDY attack. RUDY is a functions of a random process. network server attack designed to crash a web 20. for k server by sending long requests. The attack is 21. for i carried out using a tool that scans the target website and detects embedded web forms. Once characteristics that lead to abnormal traffic, as the forms have been detected, RUDY sends valid well as on the observed frequency of anomalies. HTTP POST requests with an abnormally long Thus, the method “selects” the required trajectory content-length header field, and then begins depending on the entry point and the average entering information, one byte per packet. This trajectory. type of attack is difficult to detect due to small For this example, the important question is fluctuations in incoming traffic. how the forecasting accuracy depends on the For clarity, only one case of an attack against number of a priori observations. This issue has the background of normal traffic was taken, as already been considered in [18], where it was shown in Figure 2. The average delay between shown that in 60...90 s the deviation of the transmitted packets is considered as the parameter predicted trajectory from the control one under study. decreases to 5...0%. This confirms the adequacy The prediction algorithm was applied to the of the predictive model for identifying slow DDoS process shown in Figure 2, taking as the initial attacks based on predicting network latency. observation values individual points in the time series that correspond to a partial trajectory (blue line in Figure 2). Considering this line as a control line, the first values of the time series were taken as the initial observation data, corresponding to t = 1, 30, 60 s of observations. a) t = 1 s Figure 2: Traffic patterns Figure 3a shows the forecast results for t = 1 s. Since there are few initial observational data, the process is reproduced as a whole in terms of the average value. In this case, the values of the predicted traffic in the event of an attack will be b) t = 30 s very different from the real ones (red curve). Increasing the number of observations to t = 30 s (Figure 3b) increases the reliability of further prediction and at t = 60 s we can talk about a fairly accurate prediction P ps ( s ) 0,99 . In Figure 3b and 3c curves of other colors show how forecasting will be carried out when receiving data from other control points t , = 1,k,k I , preceding the moment tk . That is, the probability of error in choosing the correct trajectory depends on the amount of raw data observed. It is logical c) t = 60 s to assume that in this case the forecast accuracy will be too dependent on the trajectory behavior Figure 3. Delay Time forecasting with observation the intervals between these points. time t = 1, 30, 60 s: ― forecast value; ― 3. Further research in the field of countering compared value; --- mean value slow DDoS attacks can be devoted to the issues of forecasting at intervals that are not covered by statistics or the operation of the method in the absence of some observations or strong data noise. 5. References [1] Enrico Cambiaso, & Gianluca Papaleo, & Giovanni Chiola, & Maurizio Aiello. (2013). Slow DOS Attacks: Definition and Categorisation. International Journal of Trust Management in Computing and Figure 4: Coordinate functions Communications. 1. 300-319. 10.1504/IJTMCC.2013.056440. Even more interesting is the question of the [2] David Holmes. Mitigating DDoS Attacks with behavior of the coordinate functions (Fig. 4). F5 Technology. [Electronic Resource] These functions are recalculated at each stage of URL: https://www.f5.com/pdf/white- calculating the predicted value and at the final papers/mitigating-ddos-attacks-tech-brief.pdf stage are constant for a certain statistical series. 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