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From: john at (John Leach)
Subject: Application level firewall

I think calling it "application level firewalling" is complicating the

I *think* that you want to be able to restrict what connections a
process makes from the machine it's running on (Like Zone Alarm does
with the little pop-ups "porn.exe wants to connect to with your credit-card details, You

I'm not sure about a nice socially engineerable GUI pop-up, but
Netfilter allows you to restrict these connections using the OUTPUT
chain on the FILTER table.  Combined with the owner matcher you can
achieve what you need.

iptables -t filter -P OUTPUT DROP (drop by default)
iptables -t filter -A OUTPUT -p tcp --dport 80 -d -m
owner --cmd-owner webbrowser -j ACCEPT

Obviously an attacker could rename their process to get the same access
so this isn't perfect, but I expect ZoneAlarm has the same issue.  You
can limit by owner uid too (--uid-owner) which is handy for ensuring
your dns server can only do dns lookups and your smtp server can only do
all the crazy things BIND does nowadays (assuming they are running as
separate users).
"Application layer firewalling" is a different matter (is this tcp port
1433 packet REALLY an SQL server connection?  Are they submitting a
query I don't like?  What the hell are they thinking connecting this to
the Internet?  Is this thread actually on topic?)

I wonder if someone has invented a mailing list topic firewall.
listtables -t filter -s -s "full disclosure" -s !
"porno" -j ACCEPT


On Fri, 2003-10-17 at 13:02, Jason Freidman wrote:
> Is there any sort of application level firewall for linux?  Something
> like Zone alarm where you can trust an application?  I think that
> openBSD has something that allows you to choose which system calls a
> program can run.
> The idea would be to restrict a bind call and connect call using kernel
> modules unless the program is in a config file.  It would make it easier
> (i would think) to lockdown a computer for outgoing connections as well
> as add a new layer of security.
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