1y ago

Calling all Linux enthusiasts! Help us create a comprehensive guide to Linux firewalls and security!

Hello fellow Linux enthusiasts!

As many of you know, Linux can be a powerful and flexible operating system, but it can also be daunting for new users, especially when it comes to securing their systems. With the abundance of information available online, it's easy to get overwhelmed and confused about the best practices for firewall configuration and basic security.

That's why I reaching out to the Linux community for help. I am looking users who are willing to share their expertise and write a comprehensive guide to Linux firewall and security.

The goal of this guide is to provide a centralized resource that covers the following topics:

 undefined

        Introduction to Linux firewalls (e.g., firewalld, ufw, etc.)
    Understanding basic security principles (e.g., ports, protocols, network traffic)
    Configuring firewalls for various scenarios (e.g., home networks, servers, VPNs)
    Best practices for securing Linux systems (e.g., password management, package updates, file permissions)
    Troubleshooting common issues and errors
    Advanced topics (e.g., network segmentation, SELinux, AppArmor)

I am looking for a well-structured and easy-to-follow guide that will help new users understand the fundamentals of Linux firewall and security, while also providing advanced users with a comprehensive resource for reference.

If you're interested in contributing to this project, please reply to this post with your experience and expertise in Linux firewall and security. We'll be happy to discuss the details and work together to create a high-quality guide that benefits the Linux community.

Thank you for your time and consideration, and im looking forward to hearing from you!

72 comments

I build Linux routers for my day job. Some advice:
your firewall should be an appliance first and foremost; you apply appropriate settings and then other than periodic updates, you should leave it TF alone. If your firewall is on a machine that you regularly modify, you will one day change your firewall settings unknowingly. Put all your other devices behind said firewall appliance. A physical device is best, since correctly forwarding everything to your firewall comes under the "will one day unknowingly modify" category.
use open source firewall & routing software such as OpenWRT and PFSense. Any commercial router that keeps up to date and patches security vulnerabilities, you cannot afford.
- i just want to also toss opnsense into that list, a long time ago it forked off pfsense and these days it offers (in my opinion) a significantly easier and better UI as well as more up to date kernel and better tools for dealing with things like buffer bloat
- Any links or thoughts on sane OpenWRT settings for a home network? I'm a networking noob but learning slowly and would love some good reading or tips.
  
  The defaults are great.
  
  Most firewalls are at their safest when you first get them i.e by default they block everything coming in. As you start doing port forwarding and the like you start making the network selectively less secure; that's when you have to pay attention.
- opinions on Ubiquiti routers?
  
  I had an EdgeRouter X for years before I started my job. They are solid devices, and I'd definitely put them above most consumer routers.
  Because they only charge for the hardware, they will eventually run into the same disincentive to provide consistent timely updates. If you do buy an Ubiquiti or similar enthusiast brand, do still keep an eye out for the CVEs that don't get patched.

No need: https://wiki.nftables.org/wiki-nftables/index.php/Quick_reference-nftables_in_10_minutes :D
Now seriously, good project.

I think firewall is the last thing you'd want to discuss with the newcomers...
- Yeah I don't even understand the point. The vast majority of people don't even need a client side firewall. The only time you need to worry about a client side of firewall is if you're on a laptop that you actually take out of your house ever or on a university or otherwise shared network. At home it's completely meaningless and a waste of CPU Cycles.
  There are significantly better ways to address security, like how to enable a sandbox like firejail or bubblewrap or enable things like apparmor, firewall is probably one of the most inconsequential parts of security these days because it's all handled by the local router
  
  Home networks are full of trash like iot devices, like smart speakers, tvs, plugs, etc. Average people should have firewalls. It’s free.
  
  Yeah, because how many people take their laptops out of their home, amiright?

This is a very broad subject. Are we talking straight iptables, or ufw/firewalld or at the app level with selinux/apparmor. Or at the firewall level like opnsense/pfsense? Or on the router side ddwrt and tomato etc. You can grab certain distros on either side, whonix/tails on the blueteam side, kali on the red team side. There are hardened kernels like zen and securelinux. There's network security, but also kernel level stuff like run levels, tpm, uefi, etc.
My real question is who is the audience for this? What is their use case, what distro are they using? What is the proposed environment?
- Problem 1: what tools do you choose?

Interesting.
What are the hosting details and contrib guidelines?
And some other random notes…
“Best practices for securing Linux” could probably be dropped. There are enough of those, and the topic could overrun the focus on firewalls. I could see a secure network section, but Linux might be too broad.
What about opening it up to FOSS firewalls and networking in general? The BSDs, Illumos, Haiku, and others could be added. Linux could be the starting point, and the others could be added as people feel like it.

I tried using a guide online one time to build a linux router/firewall onto a passively-cooled mini-computer that I could leave on a shelf with no I/O connected... basically a replacement for the garbo off-the-shelf wifi routers that die every year. It worked...mostly. The problem is that the random little things that didn't work right just were insurmountable for a linux noob who was just trying to follow a guide.
I hate that spending money on the best ones you can buy STILL die after a year or two. And now they all require you to login so even more people can inspect all my network traffic.
I'd love to see a guide that's kept up to date for building a simple router/firewall, with sections like you have above for more information so people can unlock ports for unusual stuff or whatever. I mean, in a perfect world, you install a LTS OS and set it up and forget about it for a few years. Mine was like that except it required manual intervention every time it rebooted. If that wasn't the case, it would have been perfect and I would be recommeding it to everyone.
- Instead of building one from scratch why not simply use one of the already made router operating systems? I would personally recommend opnsense, it has a nice easy to use web UI and can be setup in like maybe 20min.
  as for hardware you can use just about anything but i highly recommend these cute little dedicated router boxes. It is passively cooled, plenty powerful to handle wireguard VPN at gigabit speeds and should easily last you many many years without an issue.
  
  That's the kind of box I've been using. Just been running linux on it. It's been a few years, I'll look into opnsense, thx.
- Use openwrt on a existing device
  
  My issue is that the cheapo consumer hardware sucks. Using good software on bad hardware doesn't solve the issue. Unless I can use it on a normal computer... last I looked into it, I don't think you could.
- Can you explain to me what a router does? Is is just a PC tunnelling inbound and outbound connections? What makes it the master of the network?
  Btw in Germany we have FritzBox which doesnt suck, but seems they sell their company
  
  You got a lot of good answers to this. I'll add mine:
  A router is a device that bridges multiple physical networks (it will have at least two network interfaces) and directs traffic between them. It inspects every packet of data and decides which port to send it to.
  In a typical home here in the US, one network is your ISP (connected to your cable modem, for example) and the other is your home computers, consoles and devices via wifi or direct connection (like a NAS drive, for example).
  Generally you want a firewall to go along with your router. Instead of blindly passing all data to the correct network, it will decide whether it is allowed to pass or not based on a configured ruleset. Most consumer home wifi routers have a simple firewall built-in.
  They also have other features like "load balancing" to prioritize certain data that is more sensitive to interruptions in the data flow (like gaming) over data that isn't (like video or audio), or "DHCP servers" to hand out IP addressed to devices on the network, or "VPN tunneling" to encrypt data, etc.
  A linux-based computer is more than capable of performing all these tasks. If well-configured, it can do it much better than a consumer device, with better hardware and more reliability for less money over time (when taking reliability into account).
  
  A router routes traffic. It usually has dhcp and a firewall.
  However, most devices for consumers are a router, switch and a wireless access point. What this means is that they have a router but also Ethernet plugs in the back and a WiFi antenna
  
  There is a thing called the OSI model, which is a useful tool for understanding what different components of a computer network do. I suggest looking up that term if you want to learn more about how networks work.
  You might be familiar with the idea of IP addresses and MAC addresses. An IP address is routable, as in you can look at an IP address and tell where on the network (and broadly speaking, in the world) it is. A MAC address is assigned to the network adapter during its manufacture, it's kind of like the machine's name.
  When you get out a sheet of parchment, a well of squid ink and a quill pen and write an old fashioned letter to an acquaintance (ask your parents, they probably used to actually do this), you write both the recipients street address and their name on the envelope. The postal service uses the street address to move the letter to the correct building, and then there's probably someone in your household who gets the mail out of the mailbox and then says "Jim, this letter is for you."
  Think of a router as a post office; routers send each other data packets based on the recipient IP address. A switch works via MAC addresses and is more like your dad saying "Jim you got a letter." A hub, which is a technology we don't use anymore, would be more like your dad reading everyone's mail out loud for everyone to hear, and everyone else is just supposed to ignore what's not for them.
  Now, let's talk about a more informal definition of the word "router": The box with a bunch of wires and probably a couple antennas on it that your Wi-Fi probably comes out of. We call that little box a "router," and that's one of the many jobs it does. You can think of networking components as little building blocks, and your home router has many building blocks in it. It's a little computer with some networking hardware attached, and it likely functions as a router, an Ethernet switch, a wireless access point or two, probably your DHCP server (assigns IP addresses to devices on the network automatically), it probably serves as a firewall, mine can be a print server or a file server.

Have your tried the ArchWiki for the firewall programs you mentioned and their Security wiki as well? I usually find it resourceful and very comprehensive.

use pfsense for a firewall. Using nftables, firewalld, etc should only really come into play if on an untrusted network. Firewalls on servers can cause more problems than they solve and are easy to misconfigure.
run lynis on your Linux servers to help get them compliant with CIS benchmarks
be careful with your reverse proxies
keep things patched
run only necessary services
configure needed services conservatively
no root logins
- i just want to also toss opnsense into that list, a long time ago it forked off pfsense and these days it offers (in my opinion) a significantly easier and better UI as well as more up to date kernel and better tools for dealing with things like buffer bloat

Basically, a dummies guide on nftables and SELinux?

I'd love a good firewalld guide that's kinda tldr and would go into the details later.

Been using Linux for 8 years. Never even touched a firewall. Well one time on Ubuntu server i used ufw to open a port but that was it
- While I think firewalls are overrated, they are also dead easy to set up, and the best kind of defense is defense in depth.

Nobody:
OP: "Please do the needful."
- It reads like OP has been looking for something that is actually usable and not LLM shat garbage blog posts. Asking people directly seems like the primary way of getting any actually useful information these days.

Install OpenBSD
???
Profit!
- No thanks. I like to stay on the beaten path
  
  That's understandable. However, pf (OpenBSD's firewall system) is incredibly logical and easy to use. I never expected to write a fully operational (bloody thing worked the first time I tried it!) firewall ruleset on a two hour flight from scratch.

What kind of attacks could I expect on a Linux Machine? Especially when using bare Arch Linux and only setting up software that I consume (Minecraft Server, Zerotier)
- Arch on a server, that's gonna be fun lol
  
  There aren't many distro with a base system as tiny as Arch. It's not a bad choice at all. It's on my server since many years, working perfectly reliable. Everything except the base system is inside Podman containers. Why not?

This shouldn't be targeted at the average used who does not need firewalls nor most networking stuff. If highly invested in security, maybe AppArmor/SELinux could come handy. Other topics I find interesting would be the use of VPNs with Wireguard, setup killswitches, how to configure a system-wide Tor proxy, etc.
In stuff like that I could definitely help, depending on the conditions.

72 comments