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Wi-Fi networks can be jammed from PDAs

17:17 17 May 04

NewScientist.com news service


Wi-Fi networks can be jammed using nothing more sophisticated than a PDA and an off-the-shelf wireless networking card, the Australian Computer Emergency Response Team has warned.

Wi-Fi networks are becoming common in workplaces and elsewhere and it was known that they are vulnerable to jamming. It was thought that this would require the use of large, powerful and expensive equipment, but students at the Queensland University of Technology have now proved this wrong.

AusCERT says attacks will be hard to foil because the problem exploited is inherent in the Wi-Fi protocol. However, such an attack can only deny access to the network - it will not enable hackers to access user's data or computers.

The problem stems from how the Wi-Fi networks allocate transmission channels. As in many other networks, Wi-Fi nodes check to see if other devices are transmitting on the same frequency band before they begin sending data, to avoid "collisions" that occur when two or more devices talk simultaneously.

Like a conversation among a group of people, this works well as long as all devices are well-behaved. But it breaks down if one person or one device insists on talking loudly and continually. In essence, the Wi-Fi jamming is a denial of service attack.


Modest power

Unlike wired networks, wireless networks are accessible to any transmitter within range at the right frequency. The Queensland students showed that a PDA and wireless networking card could be combined to transmit in the required band.

Any Wi-Fi devices within range would detect the jamming signal and stop transmitting for as long as the jamming continued.

The wireless cards can only generate modest power and so will have a range limited to about 30 metres, estimates Frank Hanzlik, managing director of the US-based Wi-Fi Alliance. But the jamming signals need only be within range of one access point to affect all the computers associated with that network.

"As far as we can tell it's a denial of service capability, something that could affect any wireline or wireless network," Hanzlik told New Scientist. "The point is that are there are some low-cost commodity products that allow someone to effect it."

He adds that network operators with sophisticated management tools should be able to spot and shut down jammed access points so the rest of the network can function - and dispatch security personnel to investigate the jammed access point.


Jeff Hecht

Dalton wrote:I wonder if this would work for cellphones?

Seggybop wrote:If you used parabolic focusing on your access point, you could direct the signal only towards specific areas (where a computer is). The enemy would have to determine the line of sight of the antenna in order to attack. But the problem is that it kills a lot of the advantages of wireless...

Admiral Valdemar wrote:Probably a good reason to develop that Ultra Wide Band (UWB) technology further then.