The Temporal Key Integrity Protocol (TKIP) implementation in unspecified Cisco products and other vendors' products, as used in WPA and WPA2 on Wi-Fi networks, has insufficient countermeasures against certain crafted and replayed packets, which makes it easier for remote attackers to decrypt packets from an access point (AP) to a client and spoof packets from an AP to a client, and conduct ARP poisoning attacks or other attacks, as demonstrated by tkiptun-ng.
http://www.securityfocus.com/bid/32164
http://www.cisco.com/en/US/products/products_security_response09186a0080a30036.html
http://www.aircrack-ng.org/doku.php?id=tkiptun-ng
http://radajo.blogspot.com/2008/11/wpatkip-chopchop-attack.html
http://lists.immunitysec.com/pipermail/dailydave/2008-November/005413.html