Wednesday, January 11, 2012

WPS-enabled Wi-Fi routers are vulnerable to brute force attack

Security flaw found in Wi-Fi Protected Setup

The US Computer Emergency Readiness Team (US-CERT) warned of a security flaw in a popular tool intended to make it easier to add additional devices to a secure Wi-Fi network.

The organisation cited findings from security researcher Stefan Viehbock, who uncovered the security hole in the so-called Wi-Fi Protected Setup, or WPS, protocol, which is often bundled into Wi-Fi routers.

The WPS protocol is designed to allow unskilled home users to set up secure networks using WPA encryption without much hassle. Users are then able to type in a shortened PIN instead of a long passphrase when adding a new device to the secure network.

That method, however, also makes it much easier for hackers to break into a secure Wi-Fi network, US-CERT says. The security threat could affect millions of consumers, since the WPS protocol is enabled on most Wi-Fi routers sold today.

The basic problem is that the security of the eight-digit PIN falls dramatically with more attempts to key in the password. When an attempt fails, the hacker can figure out whether the first four digits of the code are correct. From there, it can then narrow down the possibilities on the remaining digits until the code is cracked. Viehbock said that a hacker can get into a secure Wi-Fi hotspot in about two hours using this method to exploit a vulnerability.

Here's how US-CERT describes the flaw:

When the PIN authentication fails, the access point will send an EAP-NACK message back to the client. The EAP-NACK messages are sent in a way that an attacker is able to determine if the first half of the PIN is correct. Also, the last digit of the PIN is known, because it is a checksum for the PIN. This design greatly reduces the number of attempts needed to brute force the PIN. The number of attempts goes from 108 to 104 + 103, which is 11,000 attempts in total.

It has been reported that some wireless routers do not implement any kind of lock-out policy for brute-force attempts. This greatly reduces the time required to perform a successful brute-force attack. It has also been reported that some wireless routers resulted in a denial-of-service condition, because of the brute-force attempt, and required a reboot.

US-CERT said in its warning that there is no known fix to the security problem. Instead, the group recommends that users disable the WPS function on their routers. The warning lists several wireless router vendors as selling devices that are affected by the security hole: Buffalo, D-Link, Cisco Linksys, Netgear, Technicolor, TP-Link and ZyXEL.

US-CERT indicated in its warning that it notified router vendors that are affected by the security issue in early December, but so far the vendors have not offered a response, nor have any of them issued statements.

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