Module-8Wireless LAN Security ,Vulnerabilities

and Attack Methods

CWNA Guide to Wireless LANs, Second Edition Chapter EightCWNA Official Study Guide, Fourth Edition Chapter Nine

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Objectives

• Define information security• Explain the basic security protections for IEEE

802.11 WLANs• List the vulnerabilities of the IEEE 802.11 standard• Describe the types of wireless attacks that can be

launched against a wireless network

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Security Principles: What is Information Security?

• Information security: Task of guarding digital information

• Information must be protective -on the devices that store, manipulate, and transmit the information through products, people, and procedures.

• Information that must be protected are CIA• Confidentiality

– Only authorized parties can view information

• Integrity– Information is correct and unaltered

• Availability– Authorized parties must be able to access at all times

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Security Principles: What is Information Security?

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Challenges of Securing Information

• Trends influencing increasing difficultly in information security:– Speed of attacks– Sophistication of attacks– Faster detection of weaknesses

• Day zero attacks

– Distributed attacks• The “many against one” approach • Impossible to stop attack by trying to identify and block source

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Categories of Attackers

• Six categories of attackers:• Hackers - Not malicious; expose security flaws, “ethical

attackers”

• Crackers – Violates system security with malicious intent

• Script kiddies- Break into computers to create damage

• Spies – Hired to break in and steal information

• Employees-Unhappy employees that steal, damage and change information

• Cyber-terrorists- Steal, damage and change information for ideology or extreme beliefs

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Security Attackers Profiles

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Categories of Attackers Based Upon Skill

• Three categories of attackers:

– Wannabees – Script kiddies

– Gonnabees – Moderate to high level of skill

– Killerbees –Gonnabees with very good human engineering (Social Engineering) knowledge

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Social Engineering Threats

• Social Engineering - The technique of persuading people to give you something that they should not give you (passwords, pins, codes, accounts, etc….)– One of the most dangerous and most successful

methods of hacking– The potential of rendering even the most

sophisticated security solution useless

• Sources– The Help Desk– On-site Contractors– Employees(end users)

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Eavesdropping vs. Hacking

• Eavesdropping - reading frames but not deciphering– MacStumbler– KisMac– NetStumbler– KisMet– Easy Wi-Fi Radar

• Hacking – Understanding the frames– Wireshark– OmniPeek– AiroPeek– AirMagnet– Javvin– Comm View

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Security Organizations

• Many security organizations exist to provide security information, assistance, and training

• Computer Emergency Response Team Coordination Center (CERT/CC)

• Forum of Incident Response and Security Teams (FIRST)

• InfraGard• Information Systems Security Association (ISSA)• National Security Institute (NSI)• SysAdmin, Audit, Network, Security (SANS)

Institute

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Basic IEEE 802.11 Security Protections

• Data transmitted by a WLAN could be intercepted and viewed by an attacker– Important that basic wireless security protections be built into

WLANs

• Three categories of WLAN protections:– Access control– Wired equivalent privacy (WEP)– Authentication

• Some protections specified by IEEE, while others left to vendors

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Access Control Security

• Intended to guard one of the CIA’s – Availability of information

• Wireless access control: Limit user’s access to AP– by Filtering MAC addresses

• Media Access Control (MAC) address filtering: Based on a node’s unique MAC address

• Can be defeated by Spoofing a MAC address

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Access Control Filtering

• MAC address filtering considered to be a basic means of controlling access– Requires pre-approved

authentication– Difficult to provide

temporary access for “guest” devices

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Wired Equivalent Privacy (WEP)

• Guard the Confidentiality of CIA– Ensure only authorized parties can view it

• Used in IEEE 802.11 to encrypt wireless transmissions– “Scrambling

• Cryptography: Science of transforming information so that it is secure while being transmitted or stored– scrambles” data

• Encryption: Transforming plaintext to ciphertext• Decryption: Transforming ciphertext to plaintext• Cipher: An encryption algorithm

– Given a key that is used to encrypt and decrypt messages– Weak keys: Keys that are easily discovered

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WEP Cryptography

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WEP Implementation

• IEEE 802.11 cryptography objectives:– Efficient– Exportable– Optional– Reasonably strong– Self-synchronizing

• WEP relies on secret key “shared” between a wireless device and the AP

• Same key installed on device and AP• A form of Private key cryptography or

symmetric encryption

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WEP Symmetric Encryption

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WEP Characteristics

• WEP shared secret keys must be at least 40 bits– Most vendors use 104 bits

• Options for creating WEP keys:– 40-bit WEP shared secret key (5 ASCII characters or 10

hexadecimal characters)– 104-bit WEP shared secret key (13 ASCII characters or 16

hexadecimal characters)– Passphrase (16 ASCII characters)

• APs and wireless devices can store up to four shared secret keys– Default key one of the four stored keys– Default key used for all encryption– Default key can be different for AP and client

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WEP Keys

- Key order must be the same for all devices

- Default Keys can be different for each device

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WEP Encryption ProcessStep-1 CRC ( Text) = ICV

– CRC= Cyclic Redundancy Check ICV = Integrity Check Value

• IV = Initialization Vector 24-bit changes for each encryption

• Step-2 IV + Secrete Key =“seed”• PRNG = Pseudo-Random Number• Step-3 PRNG (seed) = “Keystream”• Step-4 (Text+ICV) XOR (Keystream) =Ciphertext• Step-5 IV + Ciphertext = Transmission

A B XOR

0 0 0

1 0 1

0 1 1

1 1 0

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WEP Stream Cipher

• When encrypted frame arrives at destination:– Receiving device separates IV from ciphertext – Combines IV with appropriate secret key

• Create a keystream

– Keystream used to extract text and ICV– Text run through CRC

• Ensure ICVs match and nothing lost in transmission

• Generating keystream using the PRNG is based on the RC4 cipher algorithm– Stream Cipher

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Authentication

• IEEE 802.11 authentication: Process in which AP accepts or rejects a wireless device

• Open system authentication: – Wireless device sends association request frame to AP

• Carries info about supported data rates and service set identifier (SSID)

– AP compares received SSID with the network SSID• If they match, wireless device authenticated

• Shared key authentication: Uses WEP keys– AP sends the wireless device the challenge text– Wireless device encrypts challenge text with its WEP key and

returns it to the AP– AP decrypts returned result and compares to original challenge

text• If they match, device accepted into network

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Vulnerabilities of IEEE 802.11 Security

• IEEE 802.11 standard’s security mechanisms for wireless networks have fallen short of their goal

• Vulnerabilities exist in:– Authentication– Address filtering– WEP

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Open System Authentication Vulnerabilities

• Inherently weak– Based only on match of SSIDs– SSID beaconed from AP during passive scanning

• Easy to discover

• Vulnerabilities:– Beaconing SSID is default mode in all APs– Not all APs allow beaconing to be turned off

• Or manufacturer recommends against it

– SSID initially transmitted in plaintext (unencrypted)

• Vulnerabilities -If an attacker cannot capture an initial negotiation process, can force one to occur– SSID can be retrieved from an authenticated device– Many users do not change default SSID

• Several wireless tools freely available that allow users with no advanced knowledge of wireless networks to capture SSIDs

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Open System Authentication Vulnerabilities (continued)

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Shared Secret Key Authentication Vulnerabilities

• Attackers can view key on an approved wireless device (i.e., steal it), and then use on own wireless devices

• Brute force attack: Attacker attempts to create every possible key combination until correct key found

• Dictionary attack: Takes each word from a dictionary and encodes it in same way as passphrase– Compare encoded dictionary words against encrypted frame

• AP sends challenge text in plaintext– Attacker can capture challenge text and device’s

response (encrypted text and IV) • Mathematically derive keystream

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Shared Secret Key Attacks

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Address Filtering Vulnerabilities

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WEP Vulnerabilities

• Uses 40 or 104 bit keys– Shorter keys easier to crack

• WEP implementation violates cardinal rule of cryptography– Creates detectable pattern for attackers– APs end up repeating IVs

• Collision: Two packets derived from same IV– Attacker can use info from collisions to initiate a keystream

attack

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WEP XOR Operation

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Capturing packets

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WEP Attacks

• PRNG does not create true random number – Pseudorandom– First 256 bytes of the RC4 cipher can be determined by bytes

in the key itself

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Other Wireless Attacks: Man-in-the-Middle Attack

• Makes it seem that two computers are communicating with each other– Actually sending and receiving data with computer between

them– Active or passive

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Other Wireless Attacks: Man-in-the-Middle Attack (continued)

Figure 8-16: Wireless man-in-the-middle attack

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Other Wireless Attacks: Denial of Service (DoS) Attack

• Standard DoS attack attempts to make a server or other network device unavailable by flooding it with requests– Attacking computers programmed to request, but not respond

• Wireless DoS attacks are different:– Jamming: Prevents wireless devices from transmitting– Forcing a device to continually dissociate and re-associate with

AP

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Summary

• Information security protects the confidentiality, integrity, and availability of information on the devices that store, manipulate, and transmit the information through products, people, and procedures

• Significant challenges in keeping wireless networks and devices secure

• Six categories of attackers: Hackers, crackers, script kiddies, computer spies, employees, and cyberterrorists

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Summary (continued)

• Three categories of default wireless protection: access control, wired equivalent privacy (WEP), and authentication

• Significant security vulnerabilities exist in the IEEE 802.11 security mechanisms

• Man-in-the-middle attacks and denial of service attacks (DoS) can be used to attack wireless networks