more on New flaw takes Wi-Fi off the air

[Dave Farber <dave () farber net>]

Delivered-To: dfarber+ () ux13 sp cs cmu edu
Date: Fri, 14 May 2004 01:50:44 -0400
From: Valdis.Kletnieks () vt edu
Subject: Re: [IP] New flaw takes Wi-Fi off the air
To: dave () farber net

On Thu, 13 May 2004 19:25:28 EDT, Dave Farber <dave () farber net>  said:

> "When under attack, the device behaves as if the channel is always busy,
> preventing the transmission of any data over the wireless network," a
> security advisory (http://www.auscert.org.au/render.html?it=4091) released
> by AusCERT reads.

It's hardly a "newly discovered" flaw.  It's been known for several decades
that CSMA/CA based networks will fail if something interferes with the
detection of "quiet" on the network.

Anybody who's ever had to find a jabbering transciever or a missing terminator
on an Ethernet thin/thickwire segment knows about this "flaw".

My favorite part was that they *first* mention that you can do this jamming
with very little hardware - so you can hack up even a PDA's software to make
its wireless card jabber.  Then in what appears to be a classic case of
Just Not Getting It, they add:

        The model of a shared communications channel is a fundamental
        factor in the effectiveness of an attack on this vulnerability.
        For this reason, it is likely that devices based on the newer IEEE
        802.11a standard will not be affected by this attack where the
        physical layer uses Orthogonal Frequency Division Multiplexing
        (OFDM).

Yes, *this* attack won't work against a .11a network because the signal is
split across some 48 subchannels.

Obviously, getting a PDA that has an 802.11a card and hacking it to jabber
across all 48 subchannels (and remember - for the card to talk .11a it has to
have the circutry to transmit on the subchannels)... that's considered a
different attack.

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