The MadWifi driver provides support for Atheros based IEEE 802.11 Wireless Lan cards.
Clemens Kolbitsch and Sylvester Keil reported an error when processing beacon frames with an overly large "length" value in the "xrates" element.
A remote attacker could act as an access point and send a specially crafted packet to an Atheros based wireless client, possibly resulting in a Denial of Service (kernel panic).
There is no known workaround at this time.
All MadWifi users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=net-wireless/madwifi-ng-0.9.3.3"