The file upload capability in PHP versions 3 and 4 allows remote attackers to read arbitrary files by setting hidden form fields whose names match the names of internal PHP script variables.
https://exchange.xforce.ibmcloud.com/vulnerabilities/5190
http://archives.neohapsis.com/archives/bugtraq/2000-09/0150.html
http://archives.neohapsis.com/archives/bugtraq/2000-08/0477.html
http://archives.neohapsis.com/archives/bugtraq/2000-08/0455.html