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Hexing MAC address reveals Wifi passwords

Researcher says Belkin boxen at risk of simple substitution attack

Update The default WPA2-PSK passphrase used in some Belkin routers simply replaces a character of the device’s MAC address with another hecxadecimal character, according to security blogger Jakob Lell.

Lell describes the situation as follows:

Each of the eight characters of the default passphrase are created by substituting a corresponding hex-digit of the WAN MAC address using a static substitution table. Since the WAN MAC address is the WLAN MAC address + one or two (depending on the model), a wireless attacker can easily guess the wan mac address of the device and thus calculate the default WPA2 passphrase.

In either case, that’s problematic because it is possible to interrogate WiFi routers in order to learn their MAC address. Some models even advertise the address on the case of the device!

Lell’s revelation, which he says makes it possible to deduce passwords by drawing up a simple substitution table, means all an attacker needs to do to compromise a device is learn its MAC address and then spend a few minutes converting it into Hex.

Lell’s post on the topic suggests Belkin’s Surf N150 Model F7D1301v1, N900 Model F9K1104v1 and N450 Model F9K1105V2 are all susceptible to the attack.

He also writes that other routers may have the same issue, with only the substitution table differing.

“It is likely that other Belkin devices are affected as well,” Lell’s post says, adding that he has tried to engage the company on the issue since January 2012, without success. “Unfortunately, Belkin has not yet cooperated with us to fix the vulnerability and/or confirm a list of other affected devices,” he says.

The good news is that users need only change the password to make the poorly-coded default codes irrelevant. And we all know users are always diligent about that kind of chore and would never leave a system in an insecure state.

Belkin has responded to The Register's inquiries, saying "We have been made aware of the work recently published by two researchers at the Technische Universität Berlin regarding the default security configuration of Belkin routers, and appreciate their contribution to improved Wi-Fi security."

The responses goes on to say the company is "reviewing the details of the published research to understand its full implications" and will fix the problem if necessary, "so as to ensure our users continue to benefit from the maximum level of security possible while also guaranteeing interoperability and ease of use.” ®

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