[31811] in bugtraq
RE: ICMP pokes holes in firewalls...
daemon@ATHENA.MIT.EDU (Daniel Chemko)
Thu Sep 25 18:28:25 2003
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Date: Thu, 25 Sep 2003 15:05:07 -0700
Message-ID: <7C9884991ADAE0479C14F10C858BCDF5122E50@alderaan.smgtec.com>
From: "Daniel Chemko" <dchemko@smgtec.com>
To: "H D Moore" <sflist@digitaloffense.net>, <bugtraq@hackerfactor.com>,
<bugtraq@securityfocus.com>
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>NAT gateway has been
>detected as a ignore-the-source UDP forwarder
2.4 kernels: NAT doesn't work without ip_conntrack, and ip_conntrack
always keeps track of source IP addresses (hence its function). I can't
think of a situation for any Linux machine which allows inbound UDP
replies from other sources. Spoofing the original sender's address is a
different story, but that is pandemic of any stateless AND insecure
protocol.
>I posted about this in March of 2000, the kernel development team
response
>was that many RPC services require this functionality and it would not
be
>fixed. The reason is that many UDP-based RPC services will respond back
>to requests from an alternative interface using a different IP address
>entirely.
Just recently someone has written a conntrack handler to traverse
firewalls with RPC as you describe. No leaks to my knowledge, although I
am not too familiar with this module.
