The virtual private dial-up network (VPDN) component in Cisco IOS before 12.3 allows remote attackers to cause a denial of service (resource exhaustion) via a series of PPTP sessions, related to the persistence of interface descriptor block (IDB) data structures after process termination, aka bug ID CSCdv59309.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A5598
https://exchange.xforce.ibmcloud.com/vulnerabilities/41484
http://www.vupen.com/english/advisories/2008/1006/references
http://www.us-cert.gov/cas/techalerts/TA08-087B.html
http://www.securityfocus.com/bid/28460
http://www.cisco.com/en/US/products/products_security_advisory09186a0080969862.shtml