source: https://www.securityfocus.com/bid/21508/info

PHP is prone to a 'safe_mode' and 'open_basedir' restriction-bypass vulnerability. Successful exploits could allow an attacker to access sensitive information or to write files in unauthorized locations.

This vulnerability would be an issue in shared-hosting configurations where multiple users can create and execute arbitrary PHP script code; in such cases, the 'safe_mode' and 'open_basedir' restrictions are expected to isolate users from each other.

PHP version 5.2.0 is vulnerable to this issue.

session_save_path("/DIR/WHERE/YOU/DONT/HAVE/ACCESS\0;/DIR/WHERE/YOU/HAVE/ACCESS")