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[Full-disclosure] Nortel VPN Router Malformed Packet DoS Vulnerability
From: Roy Hills (Roy.Hillsnta-monitor.com)
Date: Tue May 31 2005 - 04:29:20 CDT
Nortel VPN Router Malformed Packet DoS Vulnerability
NTA Monitor have 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.
We believe that this is a serious vulnerability, because a single malformed
IKE packet causes the VPN router to crash. Also it is not normally
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.
We are 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
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
Patches for earlier software releases 4.76, 4.85, 4.90 and 5.00 are
expected to be available within a few weeks.
The vulnerability was first discovered on 3rd March 2005, and was
immediately reported to the customer and Nortel Networks security
team. Nortel reproduced the issue, and developed a fix. The fixed version
for the latest software was released on 27th May 2005.
We would like to thank Nortel Networks for responding promptly to this
issue, and producing a software fix to address it.
Roy Hills Tel: +44 1634 721855
NTA Monitor Ltd FAX: +44 1634 721844
14 Ashford House, Beaufort Court,
Medway City Estate, Email: Roy.Hillsnta-monitor.com
Rochester, Kent ME2 4FA,
UK WWW: http://www.nta-monitor.com/
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