The zend_hash_init function in PHP 5 before 5.2.1 and PHP 4 before 4.4.5, when running on a 64-bit platform, allows context-dependent attackers to cause a denial of service (infinite loop) by unserializing certain integer expressions, which only cause 32-bit arguments to be used after the check for a negative value, as demonstrated by an "a:2147483649:{" argument.
Exploitability
AV:NAC:MAu:NImpact
C:NI:NA:P4.3/AV:N/AC:M/Au:N/C:N/I:N/A:P