The GENERATE_SEED macro in PHP 4.x before 4.4.8 and 5.x before 5.2.5, when running on 64-bit systems, performs a multiplication that generates a portion of zero bits during conversion due to insufficient precision, which produces 24 bits of entropy and simplifies brute force attacks against protection mechanisms that use the rand and mt_rand functions.
http://security.gentoo.org/glsa/glsa-200811-05.xml
http://securityreason.com/securityalert/3859
https://exchange.xforce.ibmcloud.com/vulnerabilities/42226
https://www.redhat.com/archives/fedora-package-announce/2008-June/msg00773.html
https://www.redhat.com/archives/fedora-package-announce/2008-June/msg00779.html