Internet Explorer 6 allows user-assisted remote attackers to read arbitrary files by tricking a user into typing the characters of the target filename in a text box and using the OnKeyDown, OnKeyPress, and OnKeyUp Javascript keystroke events to change the focus and cause those characters to be inserted into a file upload input control, which can then upload the file when the user submits the form.
http://www.vupen.com/english/advisories/2006/2161
http://www.securityfocus.com/bid/18308
http://securityreason.com/securityalert/1059
http://secunia.com/advisories/20449
http://lists.grok.org.uk/pipermail/full-disclosure/2006-June/046610.html