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Cafe Latte attack steals credentials from Wi-Fi clients

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Hackers have refined a new technique for breaking into Wi-Fi networks protected by the aging Wired Equivalent Privacy (WEP).

The so-called 'Cafe Latte' attack aims to retrieve the WEP keys from the PCs of road warriors. The approach concentrates its attack on wireless clients, as opposed to earlier attacks that cracked the key on wireless networks after sniffing a sufficient amount of traffic on a network.

"At its core, the attack uses various behavioral characteristics of the Windows wireless stack along with already known flaws in WEP," explains Vivek Ramachandran, a security researcher at AirTight Networks, who will demonstrate the approach at the Toorcon hacking conference in San Diego this weekend (19-21 October). "Depending upon the network configuration of the authorised network we will show that it is possible to recover the WEP key from an isolated Client within a time slot ranging between just a few minutes to a couple of hours."

The attack relies on a laptop's attempt to connect to a WEP-protected network as a means to trick it into sending thousands of WEP-encrypted ARP (Address Resolution Protocol) requests.

ARP is a network protocol that maps between a network layer address and a data link layer hardware address. ARP, for example, is used to resolve IP addresses to their corresponding Ethernet address. This is necessary because a host in an Ethernet network can only communicate with another host if it knows the MAC address.

Manipulating this process can generate a bundle of WEP-encrypted ARP traffic. This data is then analysed to extract a WEP key.

An attacker can then present his machine as a bridge to the internet towards prospective victims, inspecting their traffic and potentially installing files on compromised PCs.

The shortcomings in WEP have been known for years. In April other researchers revealed a technique that might be used to break the protocol in under two minutes, far less than needed for the Cafe Latte attack.

Despite this, WEP remains widely used in consumer, small business and retail environments. WPA (Wi-Fi Protected Access) system replaced WEP years ago but an estimated 41 per cent of businesses continue to use WEP, Infoworld reports.

Early Wi-Fi technology fitted in retail point-of-sale terminals, and warehouses reportedly support only WEP. Hackers who obtained millions of credit card records from TJX, the giant US retailer, are thought to have used these shortcomings to break into its systems.

The Cafe Latte attack also has implications for the development of more sophisticated honeypots, according to Ramachandran and Md Sohail Ahmad, a colleague at AirTight who helped develop the approach.

"This presentation debunking the age-old myth that to crack WEP, the attacker needs to be in the RF (radio) vicinity of the authorised network," Ramachandran and Ahmad explain. ®

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