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.