The mcrypt_create_iv function in ext/mcrypt/mcrypt.c in PHP before 4.4.7, 5.2.1, and possibly 5.0.x and other PHP 5 versions, calls php_rand_r with an uninitialized seed variable and therefore always generates the same initialization vector (IV), which might allow context-dependent attackers to decrypt certain data more easily because of the guessable encryption keys.
blog.php-security.org/archives/80-Watching-the-PHP-CVS.html
bugs.php.net/bug.php?id=40999
cvs.php.net/viewvc.cgi/php-src/ext/mcrypt/mcrypt.c?r1=1.91.2.3.2.9&r2=1.91.2.3.2.10
osvdb.org/36087
secunia.com/advisories/26895
www.fortheloot.com/public/mcrypt.patch
www.mandriva.com/security/advisories?name=MDKSA-2007:187
www.novell.com/linux/security/advisories/2007_15_sr.html
www.php.net/ChangeLog-5.php
www.securityfocus.com/bid/23984