PHP 5.2.0 and 4.4 allows local users to bypass safe_mode and open_basedir restrictions via a malicious path and a null byte before a ";" in a session_save_path argument, followed by an allowed path, which causes a parsing inconsistency in which PHP validates the allowed path but sets session.save_path to the malicious path.
http://www.securityfocus.com/archive/1/453938/30/9270/threaded
http://www.openpkg.com/security/advisories/OpenPKG-SA-2007.010.html
http://www.mandriva.com/security/advisories?name=MDKSA-2007:038
http://securityreason.com/securityalert/2000
http://secunia.com/advisories/24514
http://secunia.com/advisories/24022
http://lists.suse.com/archive/suse-security-announce/2007-Mar/0003.html
http://cvs.php.net/viewcvs.cgi/php-src/ext/session/session.c?r1=1.336.2.53.2.7&r2=1.336.2.53.2.8