CVE 2008-2107
The GENERATE_SEED macro in PHP 4.x before 4.4.8 and 5.x before 5.2.5, when running on 32-bit systems, performs a multiplication using values that can produce a zero seed in rare circumstances, which allows context-dependent attackers to predict subsequent values of the rand and mt_rand functions and possibly bypass protection mechanisms that rely on an unknown initial seed.
See the 
CVE page on Mitre.org
for more details.
