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RE: Do ICMP re-directs actually work ?
From: Mike Gilles <mike.gilles () itmtech com>
Date: Wed, 31 Oct 2001 09:38:54 -0500

On a Security note:  Keep in mind that ICMP redirects (ICMP type 5 packets)
are unauthenticated.  And when ever possible it not be used and/or filtered
on any external subnet.  (e.g. There's no method of authentication; meaning
that a host will on blind faith accept an ICMP redirect.  So someone with
malicious intent could, using a third party tool, send a false redirect to a
host and cause a denial of service attack against the host by messing with
it's routing table.)  

Just my 2 cents...

 Michael John Gilles
 Lead Security Engineer, MCSE
 Ext. 204
 616.901.9720 mobile
 mike.gilles () itmtech com
 
 ITM Technology, LLC.
 5940 Tahoe DR. S.E. Suite 110
 Grand Rapids, MI 49546
 616.464.1361 office
 616.464.1362 fax


-----Original Message-----
From: Blake Frantz [mailto:blake () mc net]
Sent: Tuesday, October 30, 2001 4:28 PM
To: Naveed Anwar
Cc: pen-test () securityfocus com; ofir () sys-security com
Subject: Re: Do ICMP re-directs actually work ?




It's my understanding that the ICMP redirect is used in the following
scenario:

- host1 sends data to gateway1
- gateway1 looks for the next hop and find gateway2
- gateway2 is on the same net as host1
- gateway1 sends redirect to host1 informing it to use gateway2
- host1 traffic now leaves via gateway2

With this in mind, I *think* the redirect has to come from "pepsi"'s
gateway.  

On Win2k, verify the value of:
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Tcpip\Parameters\EnableICMP
Redirect

It's set to 1 (enable) by default.

-blake


On Tue, 30 Oct 2001, Naveed Anwar wrote:


Hi All

I have just been conducting a test in one of our labs by sending ICMP
redirects to a Windows 2000 Advanced Server using ICMPUSH. Using a
sniffer I see the packet successfully leave my machine, then again
from the target box I see the re-direct arrive. Say for example my
target machine is called Pepsi, and I tell it to redirect any packets
for a machine called Fanta to a dead gateway, hence communication to
Fanta will fail for the lifetime of the redirect.

Now my understanding is that the target server (Pepsi) should now
have updated its local routing table with respect to the Fanta
machine. Then from Pepsi I try to ping/telnet/http/ftp etc..(i.e
establish communication) to Fanta I am able to. The point is since I
told Pepsi via a redirect to send all traffic for Fanta to a
blackhole, how is the communication working.

One interesting point is that when I issue a netstat -rn to view the
routing table, I see no route update from the ICMP redirect. 

After reading Ofir's excellent paper I understand most ICMP
implementations are OS specific, therefore I guess redirects do not
work in Win2000 or Linux 6.2 which I also tested..or am I doing
something horribly wrong?

Thanks
Naveed


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This list is provided by the SecurityFocus Security Intelligence Alert (SIA)
Service. For more information on SecurityFocus' SIA service which
automatically alerts you to the latest security vulnerabilities please see:
https://alerts.securityfocus.com/

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This list is provided by the SecurityFocus Security Intelligence Alert (SIA)
Service. For more information on SecurityFocus' SIA service which
automatically alerts you to the latest security vulnerabilities please see:
https://alerts.securityfocus.com/


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