The upcoming 802.11w amendment to the 802.11 standard eliminates the 802.11 deauthentication and disassociation Denial of Service (DoS) vulnerabilities. This paper presents two other DoS vulnerabilities: one vulnerability in draft 802.11w implementations discovered by IEEE 802.11 TGw, and one new vulnerability in 802.11, which is still present in the 802.11w amendment. Attacks exploiting the first vulnerability are significantly more efficient than any known 802.11 DoS attacks, while attacks exploiting the second vulnerability have efficiency and feasability equivalent to a disassociation attack. This paper provides an experimental verification of these attacks, demonstrating their feasability using freely available software and off the shelf hardware. Finally, the root cause of these vulnerabilities is discussed and a backwards compatible solution proposed.