The build process for ypserv in FreeBSD 5.3 up to 6.1 accidentally disables access restrictions when using the /var/yp/securenets file, which allows remote attackers to bypass intended access restrictions.
https://exchange.xforce.ibmcloud.com/vulnerabilities/26792
http://www.securityfocus.com/bid/18204
http://securitytracker.com/id?1016193
http://security.freebsd.org/advisories/FreeBSD-SA-06:15.ypserv.asc