A search path issue exists in Safari. When displaying the location of a downloaded file, Safari launches Windows Explorer without specifying a full path to the executable. Launching Safari by opening a file in a specific directory will include that directory in the search path. Attempting to reveal the location of a downloaded file may execute an application contained in that directory, which may lead to arbitrary code execution. This issue is addressed by using an explicit search path when launching Windows Explorer. This issue does not affect Mac OS X systems. Credit to Simon Raner of ACROS Security for reporting this issue.

More: http://support.apple.com/kb/HT4333