The error_log function in basic_functions.c in PHP before 4.4.4 and 5.x before 5.1.5 allows local users to bypass safe mode and open_basedir restrictions via a "php://" or other scheme in the third argument, which disables safe mode.
http://secunia.com/advisories/20818
http://secunia.com/advisories/21050
http://secunia.com/advisories/21125
http://secunia.com/advisories/21546
http://securityreason.com/achievement_securityalert/41
http://securityreason.com/securityalert/1129
http://securitytracker.com/id?1016377
http://www.mandriva.com/security/advisories?name=MDKSA-2006:122
http://www.php.net/release_5_1_5.php
http://www.securityfocus.com/bid/18645
http://www.ubuntu.com/usn/usn-320-1