IBM AIX 6.1, 7.1, and 7.2 could allow a local user to exploit a vulnerability in the bellmail binary to gain root privileges.
http://www.securitytracker.com/id/1037748
http://www.securityfocus.com/bid/95891
http://aix.software.ibm.com/aix/efixes/security/bellmail_advisory2.asc