Directory traversal vulnerability in Zend Platform 2.2.1 and earlier allows remote attackers to overwrite arbitrary files via a .. (dot dot) sequence in the final component of the PHP session identifier (PHPSESSID). NOTE: in some cases, this issue can be leveraged to perform direct static code injection.
https://exchange.xforce.ibmcloud.com/vulnerabilities/28576
http://www.vupen.com/english/advisories/2006/3388
http://www.securityfocus.com/archive/1/444263/100/0/threaded
http://www.hardened-php.net/advisory_052006.128.html