Australian CERT warns of new flaw in wireless protocol

The Australian Computer Emergency Response Team issued an advisory Thursday warning of a flaw in the 802.11 wireless protocol that makes WLANs vulnerable to a denial-of-service attack.

AusCERT said the vulnerability is related to the medium access control (MAC) function of the 802.11 protocol and could allow an attacker with a low-powered portable device such as a PDA and a networking card to disrupt WLAN traffic.

The organization said WLAN devices perform Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). Key to the functioning of that procedure is the Clear Channel Assessment (CCA) procedure. An attack exploiting the vulnerability targets the CCA function at the physical layer and causes all WLAN nodes within range to defer transmission of data, according to AusCERT.

"Previously, attacks agianst the availability of IEEE 802.11 networks have required specialized hardware and relied on the ability to saturate the wireless frequency with high-power radiation, an avenue not open to discrete attack," AusCERT said in its advisory. "This vulnerability makes a successful, low-cost attack against a wireless network feasible for a semi-skilled attacker."

No comprehensive solution is available to fix the problem but AusCERT said well protected WLANS such as those for internal infrastructures should be relatively unaffected. Devices based on the newer 802.11a standard likely won't be affected.

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