TCP Syn Flood Attack Detection And Prevention

I nternational Jour nal of Comp Computer uter Tr end ends s and Tec Technology hnology (I JCTT ) – volu me 4 I ss ssue10 ue10 – Oct 2013

TCP Syn Flood Attack Detection And Prevention D.Deepthi Rani #1,T.V.Sai Krishna *2,G.Dayanandam#3,Dr.T.V.Rao*4 #1

M.Tech Student,Dept.of CSE,QISCET,Ongole,INDIA Associate Professor, Dept.of.CSE, QISCET, Ongole, INDIA #3 Professor,Dept.of.CSE,QISIT,Ongole,INDIA *4 Professor, Dept.of.CSE,KLU,Guntur,INDIA

*2

Abstract: Denial-of-Service (DoS) is a network security problem that poses a serious challenge to trustworthiness of services deployed on the servers. The aim of DoS attacks is to make services unavailable to legitimate users by flooding the victim with legitimate-like requests and current network architectures allow easy-to-launch, hard-to-stop DoS attacks. Nowadays every one relies on online transactions. These transactions involve one of the many types of denial of service attacks is known as TCP SYN Flood attack. The goal of the attacker is exhausts the victim network of resources such as bandwidth, computing power,etc.,the victim is unable to provide services to its legitimate clients and network performance is greatly deteriorated. Defending against those types of attacks is not trivial job, mainly due to the use of IP Spoofing and the destination-based routing of the Internet. This paper explains about efficient packet filtering technique using firewall to defend TCP SYN Flood attacks. Firewall scripts are written using command-line tool IP Tables in Linux to deny the suspicious traffic. Keywords: Dos Attacks, Flood Attacks, IP tables

1.

INTRODUCTION

Denial of Service(DoS) Attacks denies services to legitimate clients by flooding of legitimate looking service requests to the server. Such an attack can take many shapes, ranging from an attack on the physical IT environment, to the overloading of network connection capacity, or through exploiting application weaknesses. Gligor et al.[8] al.[8] defined DoS as: “ a group of otherwise authorized users of a specific service is said to deny service to another group of authorized users if the former group makes the specified service unavailable to the latter group for a period of time which exceeds the intended waiting time.” TCP SYN Flood attacks are the major part of the DoS attacks. According to the survey, nearly 92% of the attacks are DoS attacks. In these attacks, attackers send a succession of SYN requests to a target system in an attempt to consume enough server resources to make the system unresponsive to the legitimate clients.SYN flooding attacks are performed by the attacker submitting stream of TCP SYN packets to the target system, filling its connection request queue, and thus reducing the target system’s ability to respond to legitimate connection

ISSN: 2231-2803

requests. The common TCP timeout for unsuccessful connections is several tens of seconds, thus an attacker can easily fill the TCP SYN queue before earlier SYNs timeout. These attacks require very little computation and bandwidth commitment from the malicious users. In this attack what happens, an attacker floods the target computer with unfinished SYN requests. DDOS Attacks: A DDoS attack uses many computers to launch a coordinated DoS attack against one or more targets. Using client/server technology, the perpetrator is able to multiply the effectiveness of the DoS significantly by harnessing the resources of multiple unwitting accomplice computers which serve as attack platforms. SYN flooding attack: This attack may be used to pr event service to a system temporarily to take advantage of a trusted relationship that exists between that system and another. SYN flooding[4] is an example of DDoS attack that takes advantage of the way TCP/IP networks were designed to function. In this attack, the victim is flooded with half open connections. The client system begins by sending a SYN message to the server. The server then acknowledges the SYN message by sending SYN-ACK message to the client. The client then finishes establishing the connection by responding with an ACK message. The connection between the client and the server is then open, and the service-specific data can be exchanged between the client client and the server.

Figure 1 shows the view of this message flow:

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I nternational Jour nal of Compute Computerr Tr ends and Tec Technol hnol ogy (I JCTT ) – volu me 4 I ss ssue10 ue10 – Oct 2013

eventually fill. Then the system will be unable to accept any new incoming connections until the tables is emptied out[4]. 2.PROBLEM OVERVIEW

The scope of this report explains the concept of SYN Flood attack generation and detection by using scapy and wire shark respectively. By using net stat command and shell scripts using IP tables to deny the suspicious traffic. 3.SOFTWAREAPPLICATIONS

Fig1: TCP 3-way handshake The potential for abuse arises at the point where the server system has sent an acknowledgment(SYN-ACK) back to client but has not yest yest received th e ACK message. This is known as half-open connection. The server has built in its system memory a data structure describing all pending connections. This data structure is of finite size, and it it can be made to overflow by intentionally creating too many half open connections.Creating half-open connections is easily accomplished with IP spoofing. The attacking system sends SYN messages to the victim server system. These appear to be legitimate but in fact reference a client system that is unable to respond to the SYN-ACK messages. This means that the final ACK message will never be sent to the victim server system.

The following free software applications were used in the process of configuring configuring the SYN flood attack. Wireshark: Wireshark[7] is a network protocol analyzer. This multi platform application comes bundled with a GUI to make network troubleshooting and analysis easy to work with and view in real time. It is most often used for its packet sniffing capabilities that allow users to capture and view packets in real time across a multitude of network protocols. JAVA: JAVA is a open-source and freely available software which is used to run normal client server programme to identify both attack detection detection and prevention. prevention. NMAP(“Network Mapper”) NMAP[6] is freely available network analysis tool. NMAP is used to perform port scanning, operating system detection and host discovery etc.. Scapy: Scapy[5] is a powerful interactive packet manipulation program. It is able to forge or decode packets of a wide number of protocols, send them on a wire, capture them, match requests and replies, and much more. It can easily handle most classical tasks like scanning, trace routing, probing, unit tests, attacks on network discovery. It also performs other specific tasks that other tools cant handle. IP Tables: IP Tables[2] is a current Linux Firewall mechanism and a successor of ipfilter and ipchains. The primary purpose is packet filtering based on header fields, e.g., IP addresses, TCP and UDP ports, and TCP flags. Originally, the most popular firewall/NAT firewall/NAT package running on Linux was ipchains, but it had a number of shortcomings. To rectify this, the Netfilter[3] organization decided to create a new product called IPtables.

Fig2. SYN Flood Attack[1] Figure 2 shows the scenario of half open connection. The halfopen connections data structure on the victim server system system will

ISSN: 2231-2803


4. IMPLEMENTATION STEPS

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Fig3: Implementation steps

Step1: To establish a segregate network using virtualization. VMware Workstation is used to establish a segregate network and two UBUNTU 12.04 LTS and UBUNTU 13.04 operating systems are installed on it. Step2: Identify open ports on victim machine by using NMAP tool. If we run java client-server program on victim machine, then NMAP identifies the port related to running of client-server program on victim victim machine. Step3: Run the IP table rule on attacker machine such that victim’s kernel’s do not r eceive RSTs. Step4: Run Wire shark tool tool on victim’s machine in order to detect and analyze DoS attack. Step5: Write Shell script using IP tables to block SYN flood attacks on victim’s machine.

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Fig 4: Flow chart for SYN Flood Prevention using Shell script (using IP tables)

We can reject packets intended for unknown port

Step6: After blocking traffic using IP tables ag ain capturing and analyzing of live traffic using wire shark. The above six steps are performed as per diagram shown in Fig3.


5.EXPERIMENTAL RESULTS:

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Fig 6: Run iptable rule at attacker machine to drop RST requests

Fig 5: Identify open ports in victim machine using NMAP

Fig 7: Identify Half-open states (SYN-ACK pair)

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Fig 9: Client-server communication after prevention of TCP SYN flood attack

Fig 8: Reject TCP connections after TCP SYN Flood attack Fig 10: TCP flow graph showing after prevention prevention of SYN flood attack

6. CONCLUSION As the experiments showed a DoS environment could not actually have been created given the hardware and software used. This paper discussed python script for TCP SYN flood attack generation using scapy tool. We can spoof the IP address and flood the packets to generate attack by scapy tool. We can detect TCP SYN flood attack using client-server program and wire shark tool. The main contribution of this paper is writing shell script that includes IP tables rules, we can prevent TCP SYN flood attack along with other mitigation techniques effectively. 7. REFERENCES 1. 2. 3.

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SYN Flood Wikipedia Encyclopedia, Available: http://en.wikipedia.org/wiki/syn_flood http://www.linuxhomenetworking.com/Quick_HOWTO_:Ch14_:_Li nux_FIrewalls_Using IP tables http:// http:// www.netfilter.org/about.html


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5. 6. 7. 8.

H.Wang,D.Zhang,K.G.Shin, Detecting SYN Flooding attacks, In proceedings of the IEEE infocom,pages 000-001, New York, June 2002,IEEE http:// www.secdev.org/projects/scapy/doc/usage.html Nmap reference guide, guide, insecure.org[http://insecure.org/nmap/man1] insecure.org[http://insecure.org/nmap/man1] Wireshark, wireshark.org[http://www.w wireshark.org[http://www.wireshark.org] ireshark.org] Che-Fn Yu and virgil D.Gligor. A specification and verification method for preventing denial of service.IEEE Trans.Software Eng.,16(6):581-592,1990.

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TCP Syn Flood Attack Detection And Prevention

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