Internet Key Exchange (IKE) version 1 protocol, as implemented on Cisco IOS, VPN 3000 Concentrators, and PIX firewalls, allows remote attackers to cause a denial of service (resource exhaustion) via a flood of IKE Phase-1 packets that exceed the session expiration rate. NOTE: it has been argued that this is due to a design weakness of the IKE version 1 protocol, in which case other vendors and implementations would also be affected.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A5299
https://exchange.xforce.ibmcloud.com/vulnerabilities/27972
http://www.securityfocus.com/bid/19176
http://www.securityfocus.com/archive/1/441203/100/0/threaded
http://www.nta-monitor.com/posts/2006/07/cisco-concentrator-dos.html
http://www.cisco.com/en/US/tech/tk583/tk372/tsd_technology_security_response09186a00806f33d4.html
http://securitytracker.com/id?1016582
http://securityreason.com/securityalert/1293
http://archives.neohapsis.com/archives/bugtraq/2006-07/0531.html