WebKit in Apple Safari before 4.0 does not prevent references to file: URLs within (1) audio and (2) video elements, which allows remote attackers to determine the existence of arbitrary files via a crafted HTML document.
http://www.vupen.com/english/advisories/2011/0212
http://www.vupen.com/english/advisories/2009/1522
http://www.securityfocus.com/bid/35333
http://support.apple.com/kb/HT3613
http://secunia.com/advisories/43068
http://lists.opensuse.org/opensuse-security-announce/2011-01/msg00006.html
http://lists.apple.com/archives/security-announce/2009/jun/msg00002.html