Nortel Networks Contivity VPN Client displays a different error message depending on whether the username is valid or invalid, which could allow remote attackers to gain sensitive information.
https://exchange.xforce.ibmcloud.com/vulnerabilities/17988
http://www.securityfocus.com/bid/11623
http://www.nii.co.in/vuln/contivity.html
http://www.kb.cert.org/vuls/id/CRDY-626N7F
http://www.kb.cert.org/vuls/id/830214
http://archives.neohapsis.com/archives/fulldisclosure/2004-11/0291.html