By Dan Goodin
26 Feb 2008
Businesses using some of the more advanced methods for securing
connections to Wi-Fi access points need to take a hard look at the
configuration settings of client computers. So say researchers who have
documented a simple way to impersonate trusted networks.
The attack works on access points that use the Wi-Fi Protected Access
(WPA) in concert with Protected Extensible Authentication Protocol
(PEAP) or other so-called Extensible Authentication Protocols (EAPs).
Such technologies use public-key certificates to authenticate a trusted
network to a laptop or other connected device and provide an encrypted
SSL tunnel through which the two can communicate.
Problem is, laptops running Windows, OS X and various versions of Linux
frequently have the security settings mis-configured, according to
researchers Brad Antoniewicz and Josh Wright. Using a program called
FreeRADIUS-WPE  (short for FreeRADIUS Wireless Pwnage Edition), it's
easy to dupe the clients into connecting to imposter networks and giving
up critical information, they say.
The attack relies on a technology known as a wireless supplicant, which
sits on the client and checks the validity of a network's credentials.
All too frequently, the researchers say, it's not configured to validate
a certificate at all, or at the very least, not to properly validate a
server's RADIUS TLS certificate.
"In either of these scenarios, FreeRADIUS-WPE (our modified version of
the open source RADIUS server) can be used to gain access to the inner
authentication credentials passed in the TLS tunnel that is established
between client and the authentication server," Antoniewicz writes here
. "In some cases these protocols reveal the client's username and
password in clear text, while other cases require a brute force attack.
Due to active directory integration, these credentials may also be those
used for domain authentication."
The researchers envision a scenario where a vulnerable client could be
induced to give up sensitive information while connected to a public
hotspot that's in close proximity to a corporate access point.
Microsoft's Windows Zero Configuration (WZC) by default is set to
validate server certificates and we suspect the same can be said about
wireless supplicants contained in competing operating systems. But
Antoniewicz says these settings are frequently turned off, presumably at
the first sign of connectivity problems, and then never turned back on.
What's more, Windows users can easily be misled by prompts that ask if
they want to connect to a network whose validation doesn't check out.
"When using WZC and other supplicants, you'll want to make sure that the
client clearly validates the server certificate by only trusting
certificates that match the signing authority, and hostname of the
RADIUS server," Antoniewicz advises.
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