When do I actually need a firewall?

I’ve spent some time searching this question, but I have yet to find a satisfying answer. The majority of answers that I have seen state something along the lines of the following:

  1. “It’s just good security practice.”
  2. “You need it if you are running a server.”
  3. “You need it if you don’t trust the other devices on the network.”
  4. “You need it if you are not behind a NAT.”
  5. “You need it if you don’t trust the software running on your computer.”

The only answer that makes any sense to me is #5. #1 leaves a lot to be desired, as it advocates for doing something without thinking about why you’re doing it – it is essentially a non-answer. #2 is strange – why does it matter? If one is hosting a webserver on port 80, for example, they are going to poke a hole in their router’s NAT at port 80 to open that server’s port to the public. What difference does it make to then have another firewall that needs to be port forwarded? #3 is a strange one – what sort of malicious behaviour could even be done to a device with no firewall? If you have no applications listening on any port, then there’s nothing to access. #4 feels like an extension of #3 – only, in this case, it is most likely a larger group that the device is exposed to. #5 is the only one that makes some sense; if you install a program that you do not trust (you don’t know how it works), you don’t want it to be able to readily communicate with the outside world unless you explicitly grant it permission to do so. Such an unknown program could be the door to get into your device, or a spy on your device’s actions.

If anything, a firewall only seems to provide extra precautions against mistakes made by the user, rather than actively preventing bad actors from getting in. People seem to treat it as if it’s acting like the front door to a house, but this analogy doesn’t make much sense to me – without a house (a service listening on a port), what good is a door?

thanks_shakey_snake,

For me, it’s primarily #5: I want to know which apps are accessing the network and when, and have control over what I allow and what I don’t. I’ve caught lots of daemons for software that I hadn’t noticed was running and random telemetry activity that way, and it’s helped me sort-of sandbox software that IMO does not need access to the network.

Not much to say about the other reasons, other than #2 makes more sense in the context of working with other people: If your policy is “this is meant to be an HTTPS-only machine,” then you might want to enforce that at the firewall level to prevent some careless developer from serving the app on port 80 (HTTP), or exposing the database port while they’re throwing spaghetti at the wall wrestling with some bug. That careless developer could be future-you, of course. Then once you have a policy you like, it’s also easier to copy a firewall config around to multiple machines (which may be running different apps), instead of just making sure to get it consistently right on a server-by-server basis.

So… Necessary? Not for any reason I can think of. But useful, especially as systems and teams grow.

Petter1, (edited )

You most likely don’t need on device firewall if your in your home network behind a router that has a firewall. If you‘d disable that firewall as well and one of your devices has e.g. SSH activated using username and password, than there is nothing stopping a “hacker” or “script kiddy” from penetrating/spamming your SSH port and brute force your password. The person than can take over your PC and can e.g. install software for his botnet or install keylogger or can overtake your browser session including all authentication cookies or many other bad stuff.

If you are using puplic WiFi, I’d recommend a good on device firewall, or better just use a VPN to get an encrypted tunnel to your home (where you would need to open a port for that tho) and go into the internet from there.

TCB13, (edited )
@TCB13@lemmy.world avatar

#1 leaves a lot to be desired, as it advocates for doing something without thinking about why you’re doing it – it is essentially a non-answer.

Agreed. That’s mostly BS from people who make commissions from some vendor.

#2 is strange – why does it matter? If one is hosting a webserver on port 80, for example, they are going to poke a hole in their router’s NAT at port 80 to open that server’s port to the public. What difference does it make to then have another firewall that needs to be port forwarded?

A Firewall might be more advanced than just NAT/poking a hole, it may do intrusion detection (whatever that means) and DDoS protection

#3 is a strange one – what sort of malicious behaviour could even be done to a device with no firewall? If you have no applications listening on any port, then there’s nothing to access.

Maybe you’ve a bunch of IoT devices in your network that are sold by a Chinese company or any IoT device (lol) and you don’t want them to be able to access the internet because they’ll establish connections to shady places and might be used to access your network and other devices inside it.

#5 is the only one that makes some sense;

Essentially the same answer and in #3

If we’re talking about your home setup and/or homelab just don’t get a hardware firewall, those are overpriced and won’t add much value. You’re better off by buying an OpenWRT compatible router and ditching your ISP router. OpenWRT does NAT and has a firewall that is easy to manage and setup whatever policies you might need to restrict specific devices. You’ll also be able to setup things such as DoH / DoT for your entire network, setup a quick Wireguard VPN to access your local services from the outside in a safe way and maybe use it to setup a couple of network shares. Much more value for most people, way cheaper.

bizdelnick,

You always need it and you actually use it. The smarter question is when you need to customize its settings. Defaults are robust enough, so unless you know what and why you need to change, you don’t.

iopq,

Even if you do trust the software running on your computer, did you actually fuzz it for vulnerabilities? Heartbleed could steal your passwords even if you ran ostensibly trustworthy software.

So unless you harden the software and prove it’s completely exploit-free, then you can’t trust it.

GravitySpoiled, (edited )

I’ve got two services on my computer. One is for email, I want that this port to be open to the public WAN and one is for immich which hosts all my private pictures, I don’t want this port to be public but reachable on LAN. In my router I open the port for email but not for immich. Emal can communicate on LAN and WAN and immich only on LAN. On a foreign, untrusted LAN, like an airport I don’t want other people being able to sniff my immich traffic which is why I have another firewall setting for an untrusted LAN.

lemmyvore,

You need to understand the mindset behind running a firewall, and that mindset is that you define with mathematical precision what’s possible within the network connectivity of a device, you leave nothing to chance or circumstance, because doing so would be sloppy.

Provided you want to subscribe to this mindset, and that the circumstances of that device warrant it, and that you have the networking knowledge to pull it off, you should in theory start with a DENY policy on everything and open up specific ports for specific users and related connections only. But it’s not trivial and if you’re a beginner it’s best done directly on the server console, because you WILL break your SSH connection doing this. And of course maybe not persist the firewall rules permanently until you’ve learned more and can verify you can get in.

Now obviously this is an extreme mindset and yes you should use it in a professional setting. As a hobbyist? Up to you. In theory you don’t need a firewall if your server only exposes the services you want to expose and you were gonna expose them through the firewall anyway. In practice, keeping track on what’s running on a box and what’s using what connections can be a bit harder than that.

If you’re a beginner my recommendation is to use a dedicated router running OpenWRT with LUCI, which comes with a sensible firewall out of the box, an easy to use UI, and other goodies like an easy to use DNS+DHCP server combo and the ability to install plugins for DoH, DDNS etc.

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