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
http://www.securityfocus.com/bid/23105
http://www.mandriva.com/security/advisories?name=MDVSA-2008:126