The kernel in Apple Mac OS X before 10.7.2 does not properly prevent FireWire DMA in the absence of a login, which allows physically proximate attackers to bypass intended access restrictions and discover a password by making a DMA request in the (1) loginwindow, (2) boot, or (3) shutdown state.
http://lists.apple.com/archives/Security-announce/2011//Oct/msg00003.html