Group Warns Of Wireless DoS Attack Vulnerability

A newly-discovered vulnerability in the 802.11 standard makes it relatively easy to launch denial-of-service attacks against users of public wireless networks such as hotspots, an Australian organization said Thursday.

"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 Australian Computer Emergency Response Team (AusCert) said in an on-line alert.

AusCERT is a non-profit organization based at The University of Queensland that monitors and evaluates threats to computer networks and systems.

The alert noted that the vulnerability is related to the medium access control (MAC) function that is built into the 802.11 standard. Specifically, an attack against the clear channel assessment procedure that is part of the MAC function can cause all 802.11 clients and access points to defer transmission of data for the duration of the attack, the organization said. That would result in a cessation of network traffic.

Versions of 802.11b and 802.11g products that operate at speeds slower than 20 Mbps are vulnerable to the attack. Wireless networks working at faster speeds are not vulnerable, nor are 802.11a networks, the advisory said.Because the attack requires only basic equipment, these attacks are inexpensive to launch and are feasible "for a semi-skilled attacker," the advisory warned.

The group warned that there is no comprehensive solution for the problem because it is a flaw in the basic 802.11 standard. However, it noted that the attack ends as soon as the attacking transmission is over and that "well shielded" enterprise WLANs with a solid security infrastructure should be immune.