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S-38.310 Thesis Seminar on Networking

Technology

Topic:Investigation of Denial of

Service(Dos) attack in Wireless LAN

Author: Jing JinInstructor: Michael Hall

Supervisor: Prof. Sven-Gustav HäggmanS-72 Communication Engineering laboratory

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Presentation Outline

• Wireless LAN(WLAN) background knowledge• Denial of Service (DoS) background knowledge• Different kinds of DoS tools and attacks• The threats of DoS over WLAN• The current defending strategies

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Objectives and Scope

The objective of this Thesis is to

• describe the current research on Denial of Service (DoS) attacks in Wireless LAN (WLAN)

• to evaluate the possible solution against DoS attacks in Wireless LAN

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WLAN Architecture

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IEEE 802.11 Standards

• 802.11b is the most popular one, it operates at speeds of up to 11Mbps in 2.4GHz frequency band

• 802.11a/g standards operate at up to 54Mbps in 5GHz frequency band

• All of them follow the same MAC layer protocol• Security is the biggest problem of 802.11

standards.• Here we concentrate more on 802.11b

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HIPERLAN & HIPERLAN/2

• Developed by ETSI BRAN• The purpose is to allow flexible wireless data

networks without the need for an existing wired infrastrcture

• HIPERLAN type 1 provide 20Mbit/s with 5GHz range, multimedia application are possible

• HIPERLAN/2 is specified for short range radio access in 5GHz band for mobile terminals

• High-speed transmission, connection-oriented, QoS support, security support

• However, it is not widely used worldwide

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Chinese WLAN standard-WAPI (1)

• WLAN Authentication and Privacy Infrastructure (WAPI) is the Chinese proprietary encryption standard for IEEE 802.11

• WAPI addresses weaknesses in the original Wi-Fi secuirty specification.

• WAPI is similar in IEEE 802.11 standards but different security protocol,which is called GB 15629.11. However, WAPI is not part of IEEE 802.11 standards

• The major difference betweeen them is in authentication and privacy

• WAPI and IEEE 802.11 are not compatible

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Chinese WLAN standard-WAPI (2)

• WAPI requires both the wireless device(STA) and the access point (AP) to authenticate themselves

• The authentication is done by presenting their public key based certificate to a third party

• Once both the STA and the AP are authenticated, an Encryption Negotiation process is started

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DoS attacks (1)

• ISO 7498-2 defines DoS as ”The prevention of authorized access to resources or the delaying of time critical operations.”

• DoS is a threat that prevents legitimate users getting access to the information or resource that they need

• According to CERT/CC (CERT Coordination Center) report, DoS incidents grew at a rate around 50% per year greater than growth of Internet hosts

• DoS attacks over the Internet can be target at a user, a host computer or a network

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DoS attack (2)

In a DoS attack, an attacker attempts• To inhibit legitmate network traffic by

flooding the network with useless traffic• To deny access to a service by disrupting

connections between two parties• To block the access of a particular

individual to a service• To disrupt the specific system or service

itself

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Distributed DoS(DDoS)

• A new form of DoS, also called multiple DoS• A multitude of compromised system attack a

single target• In order to facilitate DDoS, the attacker needs to

have thousands of compromised hosts, the process is automated

• DDoS attacks become more effective and difficult to prevent

• Common DDoS tools: Trinoo, TFN, Stacheldraht

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DoS attacking tools

• Trinoo

• Stacheldraht

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Trinoo

• Trinoo is not a virus, but an attack tool released in late December 1999 that performs a distributed Denial of Service attack. Trinoo daemons were originally found in Solaris 2.x systems.

• Trinoo also has a client component that is used to control the master component. This lets the hacker control multiple master components remotely. The client can communicate with the master component by sending various commands.

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Trinoo architecture

attacker attacker

master mastermaster

daemon daemon daemon daemon daemon

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Stacheldraht (German for ”barbed wire”) (1)

• Adds encryption between the communication of the attacker and masters; adds automated update of agents

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Stacheldraht (2)

• The methods used to install the handler/agent will be the same as installing any program on a compromised UNIX system

• Ability to upgrade the agents on demand. Employs “rcp” command using a stolen account at some site as a cache.

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Stacheldraht Network

client client

handler handlerhandler

agent agent agent agent agent

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DoS is a big WLAN issue

• To initiate a DoS attack, the attacker sends a continuous stream of meaningless information to access points (APs) in WLAN

• It causes WLAN unusable• DoS over WLAN may be as simple as RF

generator in 2.4GHz band to aim the RF channel• DoS over WLAN may also be sophisticated as

spoofing 802.11 disassociation management frames to wireless terminals

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Brute force

DoS attacks are mainly implemented by

Brute force

There are two forms of brute force:

- Packet-based brute force attack

It brings significant overhead of network

- Very strong radio signals

Disrupt the network

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Brute force implementation

• Packet-based brute force attack:- use other computers on the network to send useless packets all the time

• Very strong radio signals - use a very powerful transmitter in a relatively

close rangeHowever, the use of very strong radio signal is

risky because the WLAN owners can find the attacker by AirMagnet tool.

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Types of DoS attacks over WLAN(1)

DoS attacks target many different layers of the wireless network

• Application layer(~OSI layer 7)

- sending large amount of legitimate requests to an application

• Transport layer(~OSI layer 4)

- sending many TCP connection requests to a host

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Types of DoS attacks over WLAN(2)

• Network layer (~OSI layer 3)

- conducted by sending a large amount of IP data to a network

• Data link layer (~OSI layer 2)

- data link attacks are launched to disable the ability of hosts to access the local network.

- target either a host or a network

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Types of DoS attacks over WLAN(3)

• Physical layer( ~OSI layer 1)- ”backhoe attack”, a heavy-equipment operator accidentally cut a communication cable, take down services potentially- creating a device that produces lots of noise at 2.4GHz frequency is both easy and cheap- Cordless phones have the capability to take an 802.11 network offline

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2.4GHz or 5GHz freuqncy??

• 2.4GHz WLANs can experience interference from cordless phones, microwaves...and 5GHz system is relatively free from interfering sources.

• Interoperability: 2.4G and 5GHz systems are not directly compatible.

• 5GHz systems can provide enhanced security over 2.4GHz systems because of less range.

• Densely-populated environments and multi-media applications will benefit from the use of 5GHz. 2.4GHz products are inexpensive and capable of supporting most application requirements.

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Defenses(1)

• Network Ingress and Egress Filtering• Rate limiting and Unicast reverse path

forwarding (ip verify unicast reverse_path, rate limit)

• Audit Hosts for DDoS tools (find_dos)• Audit Networks for DDoS tools (RID)• Have an Incident Response Team (IRT)• Have/enforce policies• Buy Insurance !

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Defenses (2)

• Both technical and management solutions are put into considerations

• Wi-Fi Protected Access(WPA) is a new WLAN security standard for 802.11 networks which is comprised of Temporal Key Integrity Protocol(TKIP) encryption and 802.1x technolgy.

• However, WPA is vulnerable to DoS attacks.

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Defenses (3)

The ways to respond to a DoS attack:• Absorb the attack

- plans additional capacity before an attack begins

• Degrade services-noncritical services can be degraded, or disable them if necessary

• Shut down services- Shut down services until the attack has subsided

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Defenses (4)

The fundamental protection solutions against DoS:

• updating firewalls• installing up-to-date patches• turn off network services when they are not in

use• deploy DoS detection tools, such as AirDefense,

AirMagnet• perform extensive site surveys before deploying

APs

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Conclusions (1)

• There is no comprehensive solution against DoS attacks over WLAN currently

• Take external coutnermeasures, such as tracing the attacks, enforcing related law, and enterprise usage policy systems

• 5GHz range networks are both practical and market-rewarding

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Conclusion (2)

• WLANs are not as vulnerable as the wired LAN to the DoS attacks

• If attackers cut down the power of the wired LAN, all the wired networks are down

• However, WLAN can be switched to the ad hoc configuration with laptops or other battery powered computers

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Future research works

• Simulation study and countermeasure policies by using Ethernet to construct environment for testing DoS behaviors over WLAN

• How to develop and integrate an effective wireless security policy in an enterprise

• New technologies, such as DNA fingerprints, may improve the network authentication