eggboard writes "Martin Beck, who in 2008 co-wrote a paper describing a way to inject packets into a secured Wi-Fi system, is back with a more extensive exploit. His 'Enhanced TKIP Michael Attacks' still don't allow extraction of a key, and are limited to TKIP (not AES-CCMP) WPA-protected networks. Still, he's figured out how to put in large payloads, and to extract data sent from an access point to a client — all without cracking the network key. The attack requires proximity to sniff and inject data, but it's another crack in the older key standard (TKIP) that no one with serious security interests should still be using."
Here is Beck's paper
(PDF) describing the new attacks.