PHP 5.2.1 allows context-dependent attackers to read portions of heap memory by executing certain scripts with a serialized data input string beginning with S:, which does not properly track the number of input bytes being processed.
https://exchange.xforce.ibmcloud.com/vulnerabilities/33170
https://euvd.enisa.europa.eu/vulnerability/EUVD-2007-1643
http://www.securityfocus.com/bid/23105
http://www.php-security.org/MOPB/MOPB-29-2007.html
http://www.mandriva.com/security/advisories?name=MDVSA-2008:126