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NetScreen ScreenOS 2.6 Subject to Trust Interface DoS
From: Chris Lathem <clathem () skyhawke com>
Date: 1 Feb 2002 15:06:49 -0000

Problem: NetScreen ScreenOS 2.6.1 subject to Trust 
Interface DoS Attack

Company Info: NetScreen Technologies are the 
manufacturers of some of the industry's highest 
quality VPN and firewall equipment. For more 
information please see http://www.netscreen.com.

What's affected: The ScreenOS is the heart of the 
NetScreen products. This allows for the firewall 
configuration/management. Apparently all versions 
before ScreenOS 3.1 are affected. This vulnerability 
can only occur from within the "trusted" network, or 
from a machine connected to the "trust" interface. 
External attempts will not cause any problems/DoS.

Exploit: Someone within the trusted side of the 
network can attempt a portscan on an external IP 
address. When the scan runs it appears to consume 
all of the available sessions. This, in turn, causes a 
DoS to the entire trusted interface. The only way I got 
my device to recover quickly was to perform a reset. 
A recovery might be possible without a reset, but 
after about 5 minutes of waiting, mine never 
recovered. This exploit may or may not work on your 
device. My testing was performed on a NetScreen 5. 
The higher-end, more pricier models may take longer 
to "eat up" all the available sessions, thus taking 
longer for a DoS to occur. 

I have contacted NetScreen in regards to the issue. I 
received a response back that the problem is a 
known issue. It has been addressed in ScreenOS 
3.1. An update to ScreenOS 3.1 is available for 
anyone with a NetScreen 200 or 500. For all other 
models, the update to ScreenOS 3.1 will be available 
on April 1, 2002.

I'd love to hear if anyone else has noticed this, or if 
other models are affected by this issue.

Chris Lathem
chris () lathemonline com


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