Cisco ONS15454 and ONS15327 running ONS before 3.4 have an account for the VxWorks Operating System in the TCC, TCC+ and XTC that cannot be changed or disabled, which allows remote attackers to gain privileges by connecting to the account via Telnet.
http://www.securityfocus.com/bid/6083
http://www.iss.net/security_center/static/10510.php
http://www.cisco.com/warp/public/707/ons-multiple-vuln-pub.shtml