Firewall Wizards mailing list archives
Re: Firewall best practices
From: "Darden, Patrick S." <darden () armc org>
Date: Thu, 15 Apr 2010 09:56:27 -0400
One other point I always like to make--for outgoing traffic, if you use default:deny you do your part to stop a lot of attacks that use forged IP. Your network, at least, will not be a source. E.g. Outgoing Packets Default: deny all SIP, allow only your assigned IP space, only ports X,Y,Z,P,D,Q. Of course it is even better when you mate an SIP and a port (e.g. smtp to/from your smtp gateway/server). --p On 14 April 2010 14:10, Jason Lewis <jlewis () packetnexus com> wrote:
While I believe the only allow what you need is a good rule, it's impossible to enforce in a lot of scenarios. How many small businesses have no firewall admins and do the configuration themselves? Do you think they are going to spend the time examining what ports should be open based on what their users are using? No, they will open ports until it works. Last time I checked every linksys router comes with allow all outbound by default. How many people change that? The point of my question was if you're forced into a position to open everything, what ports *should* you always block and why. The response below doesn't help that IT guy with no experience or time to research everything. For example, blocking SMB and NT RPC inbound and outbound should be a high priority. Ports 135,137-139, 445. A lot of worms are propagated via these ports and when you attempt to do DNS lookups, windows will also try to connect outbound via SMB. I had hoped someone had already put this info on the web somewhere, but I have yet to find it. Marcus's thoughts on default permit are here: http://www.ranum.com/security/computer_security/editorials/dumb/index. html Again, I agree with the thoughts, but for a hardware vendor selling to a home user or a SMB, it's never going to happen. The user wants to buy a device, plug it in and have it work. They don't want to spend time configuring things. That's reality, default deny is a dream. jas
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Current thread:
- Re: Firewall best practices R. DuFresne (Apr 13)
- <Possible follow-ups>
- Re: Firewall best practices Anton Chuvakin (Apr 14)
- Re: Firewall best practices Jason Lewis (Apr 14)
- Re: Firewall best practices Darden, Patrick S. (Apr 15)
- Re: Firewall best practices Paul D. Robertson (Apr 15)
- Re: Firewall best practices Darden, Patrick S. (Apr 15)
- Re: Firewall best practices Jason Lewis (Apr 14)
- Re: Firewall best practices John Morrison (Apr 15)
- Re: Firewall best practices Darden, Patrick S. (Apr 15)
- Re: Firewall best practices Marcus J. Ranum (Apr 15)
- Re: Firewall best practices Morty (Apr 16)
- Re: Firewall best practices Darden, Patrick S. (Apr 22)
- Re: Firewall best practices Martin Barry (Apr 22)
- Re: Firewall best practices Marcus J. Ranum (Apr 22)
- Re: Firewall best practices Martin Barry (Apr 23)
- Re: Firewall best practices Marcus J. Ranum (Apr 26)
- Re: Firewall best practices Carson Gaspar (Apr 27)
- Re: Firewall best practices ArkanoiD (Apr 28)
- Re: Firewall best practices david (Apr 26)