Risk: High
NTA Monitor has discovered a denial of service (DoS) vulnerability in the Nortel VPN Router products (which were previously known as Nortel Contivity) while performing a VPN security test for a customer.
This is potentially a serious vulnerability, because a single malformed IKE packet causes the VPN router to crash. Also it is not possible to prevent the malformed packet from reaching the router.
The vulnerability is triggered by sending a single IPsec IKE packet with a malformed ISAKMP header. On receipt of this malformed packet, the VPN router will crash immediately. The crash occurs every time such a malformed packet is sent.
Sometimes the affected VPN router will automatically reboot (which takes about five minutes), but sometimes it will stay down indefinitely and require manual intervention to restart it. In tests, the VPN router automatically rebooted around 80% of the time, and needed to be manually reset on the remaining 20%.
The VPN router does not log the malformed packet, even if the logging level is turned up to maximum. This is probably because the packet causes the router to crash before it has a chance to log it.
It is not normally possible to block public inbound access to the IKE service on the VPN router, because it is required for remote access IPsec operation. As IKE uses the UDP transport protocol, the attacker may forge the packet's source IP address to avoid identification, or to prevent the victim from blocking the traffic with ingress filtering. In addition, current IDS/IPS systems will probably not be able to detect the attack, because the malformed packet looks very similar to a normal IKE packet.
It is possible for attackers to detect and fingerprint Nortel VPN routers using the IKE fingerprinting techniques that we have previously published in VPN security white papers. Therefore users should not assume that their VPN router is invisible just because it's not published in the DNS and is not running any TCP services.
NTA is not planning to release the precise details of the malformed packet, or the proof-of-concept exploit code due to the danger of an exploit being released before the majority of the Nortel VPN users have upgraded to the fixed version.
The issues affects Nortel VPN router models 1010, 1050, 1100, 600, 1600, 1700, 2600, 2700, 4500, 4600 and 5000. We believe that all current software versions on the affected models are vulnerable.
Upgrade to software version V5.05_200 or later. Nortel customers with a valid login may obtain the new software from the Nortel technical support web site: http://www130.nortelnetworks.com/cgi-bin/eserv/cs/main.jsp
Patches for earlier software releases 4.76, 4.85, 4.90 and 5.00 are expected to be available by mid June 2005.