CVE 2012-5627
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.
See the 
CVE page on Mitre.org
for more details.
