Matt/ November 21, 2017

Over this past weekend I purchased a few upgrades to my home network/lab. One of which was upgrading my older Ubiquiti 802.11n wireless access point to the newer 802.11ac model they have out. The other purchase was a new external firewall. I had previously been running on a Cisco ASA5505, but the device is older and doesn’t support some of the newer features I would like to play with. In addition, in my current job I no longer support Cisco firewalls. So I bought a Juniper SRX300 – which should allow me to play with some new features I want, plus it can be a playground for testing things I want to do at work.

Anyways – after I cut over to my new firewall, I’ve been digging through logs to make sure that I didn’t miss anything. I have all of my device/lab logs going into an instance of Splunk Light (their free product). It makes it easy to collect and search through logs, and it’s extremely easy to set up and use. A few quick queries and I came across one or two minor things that needed to be tweaked on my firewall – but I also saw some traffic that I wasn’t sure about.

So that brings me to my question of the day: Do you know what’s going out of your network?

A lot of people I know only use firewalls to block inbound access, both in homes and businesses. For homes it’s more understandable since most average people aren’t network admins. However, it still surprises me how many businesses are willing to add a ‘permit any any’ out to the internet. Yes, I block all traffic by default through my home firewall, both inbound and outbound. Yes, it’s a bit of a pain sometimes when something isn’t quite working right – but it’s usually a quick ACL change, and overall I would rather take the minor inconvenience for the security gains.

When I originally built the firewall policy for my network, I started off simple. I know we need DNS, HTTP, and HTTPS outbound – easy enough, right? Then I started watching logs for blocked traffic and trying to decipher what else was trying to communicate outbound using another port. Some things were very easy to determine – TCP 5228 out to a Google owned IP? Yep that’s actually a known thing – a lot of Google services, like Chrome, will use this. Some other things were harder to figure out – like game consoles which use a very wide range of non-standard ports. Many of these weren’t really documented well by the console manufacturer, and meant that I spent a while between browsing forums and some trial and error.

This really gets interesting when you start digging past the stuff you know about. What about a PC in my home network that is trying (and getting blocked) to reach a few random IPs in Korea and Russia over a bunch of non-standard TCP ports? Yeah that doesn’t make me feel comfortable. Could it be a legitimate application, or is it malware? A few quick searches on the internet don’t turn up anything immediately helpful. For the time being, I’ll keep stuff like this blocked until I have time to spin up some packet captures to see what this traffic is actually doing.

For a business I feel like this type of thing is even more important than just what I’m doing at home. You certainly don’t want end users (or servers) possibly running strange applications, which might be transferring data to some unknown external party. It seems like larger companies seem to have a better handle on restricting outbound access than most smaller companies, who likely don’t have the time or see the value. However, I’ve also worked with a few larger organizations who still permit all user and server traffic out to the internet with no filtering in place.

If you’re not already blocking outbound traffic – Get some good logging in place. Use something like Splunk Light and start collecting firewall logs for everything going out of your environment. Start with the basics – create a list of the software/ports you know you’ll need to open. After a few weeks, start digging through the logs to figure out what else might need to be added to your list. Once you feel comfortable that you’ve compiled a sufficient base ruleset, schedule a time to make the change and put it in place. Start blocking the unknown traffic – and only permit when necessary.

How do you have your firewalls configured today? Do you permit everything or are you very restrictive? Comment below – I’m curious to see what other people are doing.

About Matt

Cisco certified since 2007 with a wide variety of IT and networking experiences. Just looking to share a bit of my own knowledge and experiences – the type of things I wish I would have known when I started my career.

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