The SMB File Server component in Apple Mac OS X 10.7 before 10.7.2 does not prevent all guest users from accessing the share point record of a guest-restricted folder, which allows remote attackers to bypass intended browsing restrictions by leveraging access to the nobody account.
http://www.securityfocus.com/bid/50085
http://support.apple.com/kb/HT5002
http://lists.apple.com/archives/Security-announce/2011//Oct/msg00003.html