Penetration Testing mailing list archives
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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Current thread:
- Do ICMP re-directs actually work ? Naveed Anwar (Oct 30)
- RE: Do ICMP re-directs actually work ? Ofir Arkin (Oct 30)
- Re: Do ICMP re-directs actually work ? Blake Frantz (Oct 30)
- Re: Do ICMP re-directs actually work ? foob (Oct 31)
- <Possible follow-ups>
- RE: Do ICMP re-directs actually work ? Mike Gilles (Oct 31)