Wi-Fi Protected Setup Flaw, New Attack Tool Enable Brute Force Attacks on Wireless Routersby Brian Prince, securityweek.com
December 29th 2011
The U.S. Computer Emergency Readiness Team (US-CERT) issued a warning this week about a vulnerability that may leave millions of wireless home routers open to brute force password attacks.
The flaw was uncovered by security researcher Stefan Viehbock and rests in the Wi-Fi Protected Setup (WPS), a computing standard developed by the Wi-Fi Alliance and used in the majority of wireless home routers being sold today, including products from Cisco and NETGEAR.
On Wednesday, security firm Tactical Network Solutions released an open-source tool called “Reaver” that exploits the vulnerability and conducts a brute force attack against Wi-Fi Protected Setup (WPS) registrar PINs in order to recover WPA/WPA2 passphrases.
“On average Reaver will recover the target AP's plain text WPA/WPA2 passphrase in 4-10 hours, depending on the [access point]”, said the makers of the tool. “In practice, it will generally take half this time to guess the correct WPS pin and recover the passphrase.”
According to US-CERT, Wi-Fi Protected Setup contains an authentication method known as the “external registrar” that only requires the router’s PIN.
“When the PIN authentication fails the access point will send an EAP-NACK message back to the client,” US-CERT advises. “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.”
Many wireless routers also fail to employ some sort of lockout policy after a number of failed password attempts, reducing the amount of time required to perform this kind of attack, US-CERT noted.
“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,” according to the advisory.
In a paper explaining the vulnerability, Viehbock recommended vendors institute a lock-down period after failed password attempts that is long enough to make this attack impractical. For end users, he suggested disabling WPS and upgrading their firmware to a more secure version if available.
Best practices also include using only WPA2 encryption with a strong password, disabling UPnP and enabling MAC address filtering so only trusted computers and devices can connect to the wireless network, US-CERT advised.
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