Security Basics mailing list archives
RE: Open All Outbound Ports?
From: Louis Erickson <LErickson () ariba com>
Date: Fri, 15 Nov 2002 10:39:03 -0800
By using a proxy at your NAT gateway, you can allow passive ftp from inside the firewall to work properly. You need more than port mapping to do it, but it can be done. OpenBSD and Linux's firewalls both do this transparently, I believe, at least for people inside trying to use FTP to the outside. It doesn't allow FTP back in, or didn't last time I tried. I will admit that my personal network (nothing to do with Ariba, who's network configuration I don't know, and don't care as long as the things I need to do work properly) has all outbound ports open, via NAT. Incoming is heavily filtered, but once you're in, you can connect to anywhere. I'm too lazy for myself and the other users of my resources to try and specifically allow anywhere they might connect to. (In this case irc, muds, online games and such which tend to have ports all over the map as well.) To help limit this, I make sure my (very small group of) users is educated about what not to do, and insist upon good virus scanning software. So far, so good. While I do see the risks inherent with this, I don't know a good way around it that will allow people to use all the myriad and unusual pieces of software they want to use. There's a risk assessment you have to do, and to decide what you solve through technology, and what you solve through policy. If you can't trust your staff to follow policy, that's a different problem that no technology will ever be able to solve. I also suspect that there are a lot of networks that allow any outbound connection from the private LAN, despite the misgivings of their security staff. Again, it's risk management and assessment; yes, it's risky, but not doing it irritates the other thousand people at the company, or even prevents them from doing their work successfully - what choice will management make? Sometimes they do choose security; I was at a large computer company where I had to work from home; the corporate firewall wouldn't allow me to connect to our customer's sites the ways I needed to, and they wouldn't budge on opening ports. We also had to use application level FTP and Telnet proxies, and to set the web proxy in our browsers; I don't think they allowed any raw network packets across. So, I had to work from home, and they covered part of my DSL. They had decided security was worth that cost in the few cases where the employee could really justify it. I later discovered that this was not common to the whole company, and only done at sites where they did work requiring government classifications; it was quite a shock to traveling employees that instant messaging didn't work. Other times they don't, and you have to be ready to cope with that. Make sure they understand it's a decision they're making, and that they may have to live with the consequences, and do what you have to do.
-----Original Message----- From: Chris Alliey [mailto:calliey () bellatlantic net] Sent: Wednesday, November 13, 2002 8:44 PM To: Chris Berry; security-basics () securityfocus com Subject: RE: Open All Outbound Ports? I know I don't have all the expertise that a lot of the people on this list probably have - so PLEASE take it easy on me for responding to this. I too have had a 'network engineering' team make this suggestion, and get it passed (over my objections). Even though I brought up a lot of the reasons already mentioned (security, DDOS zombies, Kazaa, limewire, ....), executives allowed them to open the ports out -- because they are the 'network security experts' in our company. I never agreed with it, but one of their reasons to open this was passive FTP. Their reason was a lot of the sites that were visited used Passive FTP, that randomly uses any port above port 1024. Can anyone comment on this? This never sat well with me, and I really didn't like it when vendors who brought laptops into our environment - discovered this, after only 1 week on site :-( As a server engineer, I've had to deal with the NIMDA and other worms/virii/.... as you can guess, that was a little worrisome. Chris -----Original Message----- From: Chris Berry [mailto:compjma () hotmail com] Sent: Monday, November 11, 2002 4:03 PM To: security-basics () securityfocus com Subject: Re: Open All Outbound Ports?From: tony tony <tonytorri () yahoo com> Our firewall group has came to me several times over thelast few >monthswanting my approval to open all of the "OUTBOUND" ports onour >firewallfacing the internet.Not a good idea. One of the most important things during a security breach is to keep the attacker from using your platform as a staging ground. By preventing them from commincating freely, you greatly retard their capabilities. For example, a trojan will probably try to "phone home" and if you have blocking set up this will show in your logs. By opening all your outbound ports you're just asking to be a DDOS zombie, warez ftp server, etc.Their argument is that this would not >significantly reduceour >security Not true, just like a military base its important to know what is going out as well as what is coming in.and it will reduce their time/effort in administration.Possibly true, although the amount of time it takes to open a set of ports can't be very long.They claim they get several requests a week to open up outbound ports >andthe number keeps growing each month.How can this be true, this would make me highly suspicious, I would want a record of all the ports they've opened over the last three months and what programs/services they opened them for. I mean unless you guys are going through some kind of major upgrade cycle their should be little or no change in your port list on a monthly basis.They want to go for the gusto...and >open up all 65,000+outbound ports.I am in the security area and they want my agreement/signoff before >theydo this. It just does not "feel/smell right" but I amlosing >ground withmy arguments. What are some good arguments I can use?Not only would I not sign off on this, I'd launch an investigation into their procedures, something definitely doesn't feel right here. I would suspect that they are allowing traffic that they shouldn't be just because someone asked for it. Kazaa for example. Chris Berry compjma () hotmail com Systems Administrator JM Associates "And here in our server room you can see our Beowolf Cluster of C64's that keeps our enterprise on the very cutting edge of technology." _________________________________________________________________ The new MSN 8: smart spam protection and 2 months FREE* http://join.msn.com/?page=features/junkmail
Current thread:
- Re: Open All Outbound Ports?, (continued)
- Re: Open All Outbound Ports? James Butcher (Nov 12)
- Re: Open All Outbound Ports? mitch_latham (Nov 11)
- Re: Open All Outbound Ports? Chris Berry (Nov 12)
- RE: Open All Outbound Ports? Chris Alliey (Nov 15)
- RE: Open All Outbound Ports? Mark Merchant (Nov 18)
- RE: Open All Outbound Ports? G. Class (Nov 21)
- Message not available
- RE: Open All Outbound Ports? Mark Merchant (Nov 22)
- RE: Open All Outbound Ports? Chris Alliey (Nov 15)