The default configuration of su in /etc/pam.d/su in GNU coreutils 5.2.1 allows local users to gain the privileges of a (1) locked or (2) expired account by entering the account name on the command line, related to improper use of the pam_succeed_if.so module.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A10029
https://exchange.xforce.ibmcloud.com/vulnerabilities/43993
http://www.securityfocus.com/bid/30363
http://securitytracker.com/id?1020552