WPA2 Vulnerability Discovered – “Hole 196″ – A Flaw In GTK (Group Temporal Key)

Well as it tends to be, when something is scrutinized for long enough and with enough depth flaws will be uncovered. This time the victim is WPA2 – the strongest protection for your Wi-fi network which is standardized.

WEP fell long ago and there’s a myriad of WEP Cracking tools available. In 2008 it was reported flaws had been found in WPA and it was partially cracked.

These factors of course shifted a lot of people to WPA2, which has now been found to have certain flaws.

Perhaps it was only a matter of time. But wireless security researchers say they have uncovered a vulnerability in the WPA2 security protocol, which is the strongest form of Wi-Fi encryption and authentication currently standardized and available.

Malicious insiders can exploit the vulnerability, named “Hole 196″ by the researcher who discovered it at wireless security company AirTight Networks. The moniker refers to the page of the IEEE 802.11 Standard (Revision, 2007) on which the vulnerability is buried. Hole 196 lends itself to man-in-the-middle-style exploits, whereby an internal, authorized Wi-Fi user can decrypt, over the air, the private data of others, inject malicious traffic into the network and compromise other authorized devices using open source software, according to AirTight.

The researcher who discovered Hole 196, Md Sohail Ahmad, AirTight technology manager, intends to demonstrate it at two conferences taking place in Las Vegas next week: Black Hat Arsenal and DEF CON 18.

It’s a pretty interesting attack and leverages a man-in-the-middle style exploit to decrypt data from the wire and inject malicious packets onto the network.

The researched Md Sohail Ahmad is going to demo the exploit at 2 upcoming conferences (Black Hat and DEF CON 18) so I’ll be looking out for the slides and videos on that. We’ll have to wait and see if this is another ‘mostly theoretical‘ attack – or something that can actually be implemented in the wild.

The Advanced Encryption Standard (AES) derivative on which WPA2 is based has not been cracked and no brute force is required to exploit the vulnerability, Ahmad says. Rather, a stipulation in the standard that allows all clients to receive broadcast traffic from an access point (AP) using a common shared key creates the vulnerability when an authorized user uses the common key in reverse and sends spoofed packets encrypted using the shared group key.

Ahmad explains it this way:

WPA2 uses two types of keys: 1) Pairwise Transient Key (PTK), which is unique to each client, for protecting unicast traffic; and 2) Group Temporal Key (GTK) to protect broadcast data sent to multiple clients in a network. PTKs can detect address spoofing and data forgery. “GTKs do not have this property,” according to page 196 of the IEEE 802.11 standard.

These six words comprise the loophole, Ahmad says.

The upside is that the attack is limited to people who can genuinely authenticate to the network first, the downside that means large organizations using WPA2 in trouble – as generally most damage comes from the inside.

It’s also something to think about when connecting to ISP/public Wi-fi hotspots using WPA2 encryption.

I’m sure there will be more news about this soon.

Source: Network World (Thanks Austin)

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