It is a well known problem for many of the firewall appliances including Sonicwall, Netscreen, PIX etc. The problem is that the traffic on trusted network interface is partially assumed secure. If firewall uses port translation for the outgoing connection they are of course limited by <2^16 ports per IP once all of them are used, you are in trouble. Of course if the firewall is well designed, it will tell you in a log that maximum # of connections is reached and it will not allow connection to management interface until there will be available connection. Some firewalls of course will just shut down management interface like did the Sonicwall up until about a year ago. This IS a bug and should be fixed, however other than that there is not much you can do. Some firewalls can have multiple IP addresses just for increasing maximum # of connections. If maximum number of connections specified is exceeded - that is a problem of system administrator. Higher end firewalls have some QoS algorithms implemented to protect you from that condition though. Also in some implementation you might get away with using NAT for the host that will produce large amount of connections - but then you got physical limitations of different memory levels. Regards, Alexander Poizner Systems Security Engineer HIP Interactive Corp. (416) 249-7555 x206 -----Original Message----- From: Chris Lathem [mailto:clathemat_private] Sent: Friday, February 01, 2002 10:07 To: bugtraqat_private Subject: NetScreen ScreenOS 2.6 Subject to Trust Interface DoS 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. Cheers, Chris Lathem chrisat_private http://www.lathemonline.com
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