=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 == https://ceur-ws.org/Vol-3200/paper6.pdf
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 ) +  Vvv ( 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 ) =  Dvv2 ( 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 ) =         Dvv ( 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 , jk , 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

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