Great Circle Associates Firewalls
(February 1994)

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Subject: Re: restricting Internet Access
From: hp90101 @ internet . sbi . com (Harry Protoolis)
Date: Tue, 8 Feb 94 13:00:45 GMT
To: Rens . Schipper @ rivm . nl
Cc: firewalls @ greatcircle . com


We restrict all connections to the internet via our firewall. I think that
unless you control outgoing connections you do create a significant security

As an example one of the ways in which the recent sendmail hole was exploited
was by planting a program on your mailhost that would attempt to open
a connection to a remote, unfriendly, host. This would allow an attacker
onto your system from outside and the connection would appear to have
been initiated *from the inside*. This would have beaten many 'packet
filtering' based firewall schemes.

There is always a tradeoff to be made between ease of use and security, a
great deal depends on what you are trying to achieve.

Harry Protoolis		"Sons of the South, make a choice between ...
harry @
 london .
 sbil .
 co .
 uk	The land that belongs to the lord and the Queen
			And the land that belongs to you." - Henry Lawson
			(with apologies for the sexist language)

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