Description

A vulnerability exists in hardware implementations of the IEEE
802.11 wireless protocol[1] that allows for a trivial but effective
attack against the availability of wireless local area network
(WLAN) devices.

An attacker using a low-powered, portable device such as an
electronic PDA and a commonly available wireless networking card
may cause significant disruption to all WLAN traffic within range,
in a manner that makes identification and localisation of the
attacker difficult.

The vulnerability is related to the medium access control (MAC)
function of the IEEE 802.11 protocol. WLAN devices perform Carrier
Sense Multiple Access with Collision Avoidance (CSMA/CA), which
minimises the likelihood of two devices transmitting
simultaneously. Fundamental to the functioning of CSMA/CA is the
Clear Channel Assessment (CCA) procedure, used in all
standards-compliant hardware and performed by a Direct Sequence
Spread Spectrum (DSSS) physical (PHY) layer.

An attack against this vulnerability exploits the CCA function at
the physical layer and causes all WLAN nodes within range, both
clients and access points (AP), to defer transmission of data for
the duration of the attack. When under attack, the device behaves
as if the channel is always busy, preventing the transmission of
any data over the wireless network.
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