PHP 4 before 4.4.5 and PHP 5 before 5.2.1, when using an empty session save path (session.save_path), uses the TMPDIR default after checking the restrictions, which allows local users to bypass open_basedir restrictions.
h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&objectID=c01056506
h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&objectID=c01086137
secunia.com/advisories/25423
secunia.com/advisories/25850
www.php-security.org/MOPB/MOPB-36-2007.html
www.securityfocus.com/bid/23183
www.vupen.com/english/advisories/2007/1991
www.vupen.com/english/advisories/2007/2374
exchange.xforce.ibmcloud.com/vulnerabilities/33550