FreeBSD 4.5 and earlier, and possibly other BSD-based operating systems, allows local users to write to or read from restricted files by closing the file descriptors 0 (standard input), 1 (standard output), or 2 (standard error), which may then be reused by a called setuid process that intended to perform I/O on normal files.
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc
archives.neohapsis.com/archives/vulnwatch/2002-q2/0033.html
online.securityfocus.com/archive/1/268970
online.securityfocus.com/archive/1/269102
www.ciac.org/ciac/bulletins/m-072.shtml
www.iss.net/security_center/static/8920.php
www.kb.cert.org/vuls/id/809347
www.osvdb.org/6095
www.securityfocus.com/bid/4568