Cisco VPN 3000 Concentrator 3.6(Rel) and earlier, and 2.x.x, when configured to use internal authentication with group accounts and without any user accounts, allows remote VPN clients to log in using PPTP or IPSEC user authentication.
https://exchange.xforce.ibmcloud.com/vulnerabilities/10017
http://www.securityfocus.com/bid/5613
http://www.cisco.com/warp/public/707/vpn3k-multiple-vuln-pub.shtml