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Communication Security: Wireless • Chapter 4 223

have to either identify the WEP secret key or capture the key through malware or
stealing the user’s notebook.

Protecting Against Spoofing and Unauthorized Attacks

Protecting against these attacks involves adding several additional components to
the wireless network.The following are examples of measures that can be taken:
■ Using an external authentication source such as RADIUS or SecurID, will
prevent an unauthorized user from accessing the wireless network and the
resources with which it connects.

■ Requiring wireless users to use a VPN to access the wired network also
provides a significant stumbling block to an attacker.

■ Another possibility is to allow only SSH access or SSL-encrypted traffic
into the network.

■ Many of WEP’s weaknesses can be mitigated by isolating the wireless net-
work through a firewall and requiring that wireless clients use a VPN to
access the wired network.

Network Hijacking and Modification

Numerous techniques are available for an attacker to “hijack” a wireless network or
session.And unlike some attacks, network and security administrators may be
unable to tell the difference between the hijacker and a legitimate “passenger.”
Many tools are available to the network hijacker.These tools are based on basic
implementation issues within almost every network device available today.As
TCP/IP packets go through switches, routers, and APs, each device looks at the
destination IP address and compares it with the IP addresses it knows to be local. If
the address is not in the table, the device hands the packet off to its default gateway.
This table is used to coordinate the IP address with the MAC addresses that are
known to be local to the device. In many situations, this is a dynamic list that is
compiled from traffic passing through the device and through Address Resolution
Protocol (ARP) notifications from new devices joining the network.There is no
authentication or verification that the request received by the device is valid.Thus,
a malicious user is able to send messages to routing devices and APs stating that his
MAC address is associated with a known IP address. From then on, all traffic that
goes through that router destined for the hijacked IP address will be handed off to
the hacker’s machine.

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