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Vulnerability Note VU#723755

WiFi Protected Setup PIN brute force vulnerability


The WiFi Protected Setup (WPS) PIN is susceptible to a brute force attack. A design flaw that exists in the WPS specification for the PIN authentication significantly reduces the time required to brute force the entire PIN because it allows an attacker to know when the first half of the 8 digit PIN is correct. The lack of a proper lock out policy after a certain number of failed attempts to guess the PIN on some wireless routers makes this brute force attack that much more feasible.

I. Description

WiFi Protected Setup (WPS) is a computing standard created by the WiFi Alliance to ease the setup and securing of a wireless home network. WPS contains an authentication method called "external registrar" that only requires the router's PIN. By design this method is susceptible to brute force attacks against the PIN.

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.

II. Impact

An attacker within range of the wireless access point may be able to brute force the WPS PIN and retrieve the password for the wireless network, change the configuration of the access point, or cause a denial of service.

III. Solution

We are currently unaware of a practical solution to this problem.

Disable WPS.

Although the following will not mitigate this specific vulnerability, best practices also recommend only using 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.

Vendor Information

VendorStatusDate NotifiedDate Updated
Belkin, Inc.Affected2011-12-27
Buffalo IncAffected2011-12-27
D-Link Systems, Inc.Affected2011-12-052011-12-27
Linksys (A division of Cisco Systems)Affected2011-12-052011-12-27
Netgear, Inc.Affected2011-12-052011-12-27



Thanks to Stefan Viehböck for reporting this vulnerability.

This document was written by Jared Allar.

Other Information

Date Public:2011-12-27
Date First Published:2011-12-27
Date Last Updated:2011-12-27
CERT Advisory: 
US-CERT Technical Alerts: 
Severity Metric:7.44
Document Revision:21

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