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Some Cisco Wi-Fi access points have a vulnerability that could allow a hacker to redirect traffic outside the enterprise or gain access to an entire corporate network, a security company has claimed.

At the root of the problem is the way that new Cisco APs are added to a network, according to AirMagnet, a wireless network security company that discovered the problem.

Existing APs broadcast information about the nearby network controller they communicate with. That way, when an enterprise hangs a new AP, that AP listens to information broadcast by other APs and knows which controller to connect to.

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However, the existing APs broadcast that information, including the controller's IP address and MAC address, unencrypted. Sniffing that information out of the air is relatively simple and can be done with free tools like NetStumbler, said Wade Williamson, director of product management at AirMagnet.

Armed with the information that the APs broadcast, a person could target a controller with a denial of service attack, for example, and take down a section of the network, Williamson said. But the attacker would likely have to be physically on-site to do that, he said.

The bigger potential is that a person could "skyjack" a new AP by getting the AP to connect to a controller that is outside of the enterprise. That would become "the mother of all rogue APs," Williamson said. "You could almost create a back door using a wireless AP." Rogue APs are typically those that employees connect to a corporate network without permission.

It could even happen accidentally. The Cisco AP might hear broadcasts from a legitimate neighbouring network and mistakenly connect to that network, he said. Or a hacker could create that same scenario intentionally in order to take control of the AP, he said.

A hacker on the outside with control of that AP could see all the traffic connecting over that AP, but also has the potential to access the enterprise's full network, Williamson said.

The vulnerability affects all of Cisco's "lightweight" APs, meaning the kind that work in conjunction with a controller, he said. That includes most of the APs Cisco has released since it acquired Airespace in 2005, he said.

Cisco spokesman Ed Tan said AirMagnet has alerted the company to the problem and that Cisco is investigating. Cisco said it takes security vulnerabilities "very seriously."

"Our standard practice is to issue public Security Advisories or other appropriate communications that include corrective measures so customers can address any issues," the company said in a statement. "For that reason we do not provide comment on specific vulnerabilities until they have been publicly reported - consistent with our well-established disclosure process."

Although the vulnerability could cause serious consequences, exploiting it wouldn't be easy. A hacker would have to be nearby when an enterprise happened to be hanging a new AP that was looking to connect to the network.

Enterprises using Cisco APs can prevent the skyjacking situation from occurring by turning off the over-the-air provisioning feature that allows the AP to automatically connect to the nearest controller. But even when that feature is turned off, the existing APs broadcast the details about the controller unencrypted, so a hacker could still collect that information, Williamson said.

AirMagnet discovered the issue when a customer asked for help after getting repeated alarms about unencrypted broadcast traffic on its wireless network. All of that traffic should have been encrypted and the company was preparing for a stringent audit, Williamson said. As AirMagnet dug deeper, it discovered the source of the unencrypted information, he said.

He expects Cisco to come up with a way for customers to shut off the broadcasts or obscure them.

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