Oracle MySQL and MariaDB 5.5.x before 5.5.29, 5.3.x before 5.3.12, and 5.2.x before 5.2.14 does not modify the salt during multiple executions of the change_user command within the same connection which makes it easier for remote authenticated users to conduct brute force password guessing attacks.
https://bugzilla.redhat.com/show_bug.cgi?id=883719
http://security.gentoo.org/glsa/glsa-201308-06.xml