A flaw in a protocol used by Cisco Systems' VPN 3000 Series virtual private networking kit can open up firms to a denial of service attack, but it cannot be patched.
The vulnerability is in the Internet Key Exchange (IKE) protocol, which enables remote IPsec (IP Security) VPN access.
The flaw can allow attackers to cripple VPN 3000 Series kit by flooding it with IKE requests, and making it unable to handle legitimate traffic.
The vulnerability has been disclosed by UK security research firm NTA Monitor, and confirmed by Cisco.
Cisco says the fault is not vendor specific and affects version 1 of the IKE protocol, so other suppliers’ systems that use this protocol may also be vulnerable, said Cisco.
Cisco's VPN 3000 Series concentrators are used at firms to support anything from between 200 and 10,000 simultaneous IPSec remote access users.
Other Cisco products that use IKE version 1 include the Adaptive Security Appliance (ASA) line, the PIX firewall platform and the very widely used Cisco Internetworking Operating System (IOS) software.
Cisco said it would work on producing workarounds to the problem as a patch was not really possible, considering the fault lies with the protocol itself.
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