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Re: Security Problems with Linux 2.2.x IP Masquerading
From: Nigel.Metheringham () VDATA CO UK (Nigel Metheringham)
Date: Tue, 28 Mar 2000 20:45:47 +0100

The UDP masquerading code only checks the DESTINATION PORT to
determine if a packet coming from the external network is to be
forwarded inside.

this is due to a number of hosts/services returning UDP from an IP
other than that which the original UDP packet went to - for example it
is frequently the case that NFS servers just use the interface ip
address "closest" to that which the NFS op came from.

I'll give this some thought to work out a way of narrowing this hole (I
don't think it can be completely closed without causing other problems).

However, in general I would not advise the use of UDP masq for a
firewalling gateway - since the only thing that people are normally
putting through the UDP side is DNS, you are much better advised to put
a decent caching name server on the gateway box and block UDP through


[ - Opinions expressed are personal and may not be shared by VData - ]
[ Nigel Metheringham                  Nigel.Metheringham () VData co uk ]
[ Phone: +44 1423 850000                         Fax +44 1423 858866 ]

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