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?

pixelscript,

This question reads a bit to me like someone asking, “Why do trapeze artists perform above nets? If they were good at what they did they shouldn’t fall off and need to be caught.”

Do you really need a firewall? Well, are you intimately familiar with every smidgeon of software on your machine, not just userland ones but also system ones, and you understand perfectly under which and only which circumstances any of them open any ports, and have declared that only the specific ports you want open actually are at every moment in time? Yes? You’re that much of a sysadmin god? Then no, I guess you don’t need a firewall.

If instead you happen to be mortal like the rest of us who don’t read and internalize the behaviors of every piddly program that runs or will ever possibly run on our systems, you can always do what we do for every other problem that is too intensive to do manually: script that shit. Tell the computer explicitly which ports it can and cannot open.

Luckily, you don’t even have to start from scratch with a solution like that. There are prefab programs that are ready to do this for you. They’re called firewalls.

Kalcifer,
@Kalcifer@sh.itjust.works avatar

Tell the computer explicitly which ports it can and cannot open.

Isn’t this all rather moot if there is even one open port, though? Say, for example, that you want to mitigate outgoing connections from potential malware that gets installed onto your device. You set a policy to drop all outgoing packets in your firewall; however, you want to still use your device for browsing the web, so you then allow outgoing connections to DNS (UDP, and TCP port 53), HTTP (TCP port 80), and HTTPS (TCP port 443). What if the malware on your device simply pipes its connections through one of those open ports? Is there anything stopping it from siphoning data from your PC to a remote server over HTTP?

pixelscript,

The point of the firewall is not to make your computer an impenetrable fortress. It’s to block any implicit port openings you didn’t explicitly ask for.

Say you install a piece of software that, without your knowledge, decides to spin up an SSH server and start listening on port 22. Now you have that port open as a vector for malware to get in, and you are implicitly relying on that software to fend it off. If you instead have a firewall, and port 22 is not one of your allowed ports, the rogue software will hopefully take the hint and not spin up that server.

Generally you only want to open ports for specific processes that you want to transmit or listen on them. Once a port is bound to a process, it’s taken. Malware can’t just latch on without hijacking the program that already has it bound. And if that’s your fear, then you probably have a lot of way scarier theoretical attack vectors to sweat over in addition to this.

Yes, if you just leave a port wide open with nothing bound to it, either via actually having the port reserved or by linking the process to the port with a firewall rule, and you happened to get a piece of actual malware that scanned every port looking for an opening to sneak through, sure, it could. To my understanding, that’s not typically what you’re trying to stop with a firewall.

In some regards a firewall is like a padlock. It keeps out honest criminals. A determined criminal who really wants in will probably circumvent it. But many opportunistic criminals just looking for stuff not nailed down will probably leave it alone. Is the fact that people who know how to pick locks exist an excuse to stop locking things because “it’s all pointless anyway”?

LoveSausage,

When you are attacked. Ok so when are you attacked , as soon as you connect outside. So unless you are air gapped you need a firewall.

bionicjoey,

TempleOS doesn’t need one

crony,
@crony@lemmy.cronyakatsuki.xyz avatar

You always need a firewall, no other answer’s.

Why do you think windows and most linix distributions come packaged with one?

Kalcifer,
@Kalcifer@sh.itjust.works avatar

You always need a firewall, no other answer’s.

Okay, but why? That’s kind of the point of why I made this post, as is stated in the post’s body.

crony, (edited )
@crony@lemmy.cronyakatsuki.xyz avatar

To keep your system secure no matter what, you open up only the ports you absolutely need.

People will always make a mistake while configuring software, a firewall is there to make sure that error is caught. With more advanced firewall’ you can even make sure only certain app’s have access to the internet to make sure only what you absolutely need toconnect to the internet does.

In general it’s for security, but can also be privacy related depending on how deep you want to get into it.

EDIT: It isnt about not trusting other devices on your netork,or software you run, or whether you are runni g a server. It’s about general security of your system.

avidamoeba, (edited )
@avidamoeba@lemmy.ca avatar

Always, as others have said.

smb,

As i see it, the term “firewall” was originally the neat name for an overall security concept for your systems privacy/integrity/security. Thus physical security is (or can be) as well part of a firewall concept as maybe training of users. The keys of your server rooms door could be part of that concept too.

In general you only “need” to secure something that actually is there, you won’t build a safe into the wall and hide it with an old painting without something to put in it or - could be part of the concept - an alarmsensor that triggers when that old painting is moved, thus creating sort of a honeypot.

if and what types of security you want is up to you (so don’t blame others if you made bad decisions).

but as a general rule out of practice i would say it is wise to always have two layers of defence. and always try to prepare for one “error” at a time and try to solve it quickly then.

example: if you want an rsync server on an internet facing machine to only be accessible for some subnets, i would suggest you add iptables rules as tight as possible and also configure the service to reject access from all other than the wanted addresses. also consider monitoring both, maybe using two different approaches: monitor the config to be as defined as well as setup an access-check from one of the unwanted, excluded addresses that fires an alarm when access becomes possible.

this would not only prevent those unwanted access from happening but also prevent accidental opening or breaking of config from happen unnoticed.

here the same, if you want monitoring is also up to you and your concept of security, as is with redundancy.

In general i would suggest to setup an ip filtering “firewall” if you have ip forwarding activated for some reason. a rather tight filtering would maybe only allow what you really need, while DROPping all other requests, but sometimes icmp comes in handy, so maybe you want ping or MTU discovery to actually work. always depends on what you have and how strong you want to protect it from what with what effort. a generic ip filter to only allow outgoing connections on a single workstation may be a good idea as second layer of “defence” in case your router has hidden vendor backdoors that either the vendor sold or someone else simply discovered. Disallowing all that might-be-usable-for-some-users-default-on-protocols like avahi & co in some distros would probably help a bit then.

so there is no generic fault-proof rule of thumb…

to number 5.: what sort of “not trusting” the software? might, has or “will” have: a. security flaws in code b. insecurity by design c. backdoors by gov, vendor or distributor d. spy functionality e. annoying ads as soon as it has internet connection f. all of the above (now guess the likely vendors for this one)

for c d and e one might also want to filter some outgoing connection…

one could also use an ip filtering firewall to keep logs small by disallowing those who obviously have intentions you dislike (fail2ban i.e.)

so maybe create a concept first and ask how to achieve the desired precautions then. or just start with your idea of the firewall and dig into some of the appearing rabbit holes afterwards ;-)

regards

lemmyreader, (edited )

Firewall for incoming traffic :

  • If you a home user with your computer or laptop inside a LAN you would not really need a firewall, unless you start to use applications which expose its ports to 0.0.0.0 rather than 127.0.0.1 (I believe Redis server software did this a few years ago) and do not trust other users or devices (smart home devices, phones, tablets, modems, switches and so on) inside your LAN.
  • If you are running a server with just a few services, for example ssh, smtp, https, some hosting company people I knew argue that no firewall is needed. I am not sure, my knowledge is lacking.

Application firewalls, watching also outgoing traffic :

If you compare Linux with some other Operating System you will see that on Linux for years an application firewall was non existing. But there is a choice now : opensnitch This can be useful if you run desktop applications that you do not fully trust, or want more control.

possiblylinux127,

Firewalls are necessary for least privilege. You only give something access that needs access.

Additionally you should not port forward and especially not port 80.

c0mbatbag3l,
@c0mbatbag3l@lemmy.world avatar

Yeah like JFC the most insecure way to access the Internet let’s just open it up to the whole world.

ShittyBeatlesFCPres,

I think it’s better to have one but you probably don’t need multiple layers. When I’m setting up servers nowadays, it’s typically in the cloud and AWS and the like typically have firewalls. So, I don’t really do much on those machines besides change ports to non-standard things. (Like the SSH port should be a random one instead of 22.)

But you should use one if you don’t have an ecosystem where ports can be blocked or forwarded. If nothing else, the constant login attempts from bots will fill up your logs. I disable password logins on web servers and if I don’t change the port, I get a zillion attempts to ssh using “admin” and some common password on port 22. No one gets in but it still requires more compute than just blocking port 22 and making your SSH port something else.

MajorMajormajormajor,

It seems that the consensus from all the comments is that you do in fact need a firewall. So my question is how does that look exactly? A hardware firewall device directly between modem and router? I using the software firewall on the router enough? Or, additionally having software firewall installed on all capable devices on the network? A combination of the above?

possiblylinux127,

I use the firewall built into Proxmox with a device running openwrt

treadful,
@treadful@lemmy.zip avatar

Depends on your setup. I got a network-level firewall+router setup between my modem and my LAN. But also, got firewalld (friendly wrapper on iptables) on every Linux device I care about because I don’t want to unintentionally expose something to the network.

hm, guess maybe I should find something for Android and my Windows boxes.

rwhitisissle, (edited )

And like most things related to Linux on the internet, the consensus is generally incorrect. For a typical home user who isn’t opening ports or taking a development laptop to places with unsecure wifi networks, you don’t really need a firewall. It’s completely superflous. Anything you do to your PC that causes you genuine discomfort will more than likely be your own fault rather than an explicit vulnerability. And if you’re opening ports on your home network to do self-hosting, you’re already inviting trouble and a firewall is, in that scenario, a bandaid on a sucking chest wound you self-inflicted.

atzanteol,

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.

You say that like that isn’t providing value. How many services are listening on a port on your system right now? Run ‘ss -ltpu’ and prepare to be surprised.

Security isn’t about “this will make you secure” it’s about layers of protection and probability. It’s a “good practice” because people make mistakes and having a second line of defense helps reduce the odds of a hack.

treadful,
@treadful@lemmy.zip avatar

Security isn’t about “this will make you secure” it’s about layers of protection and probability. It’s a “good practice” because people make mistakes and having a second line of defense helps reduce the odds of a hack.

AKA Defense In Depth and should be considered for any type of security.

c0mbatbag3l,
@c0mbatbag3l@lemmy.world avatar

In the military when learning ORM we called this the “swiss cheese” theory.

The more layers of sliced swiss cheese, the fewer holes that go all the way through.

utopiah,

When you expose ports to the Internet. It’s honestly interesting to setup a Web server with the default page on it and see how quickly you get hits on it. You don’t need to register a DNS or be part of an index anywhere. If you open a port (and your router does forward it) then you WILL get scanned for vulnerabilities. It’s like going naked in the forest, you sure can do that but clothes help, even if it’s “just” again ivy or random critters. Now obviously the LONGER you run naked or leave a computer exposed, the most likely you are to get a bad bug.

Feathercrown,

Can confirm. As an example, I’m developing a game server that runs a raw socket connection over the Telnet port. Within 10 minutes of opening the port, I reliably get requests trying to use Telnet to enable command mode or login as admin. People are constantly scanning.

mvirts,

Ya. And sometimes hosting companies run active scans on customer machines. I get a crazy number of login attempts over ssh. I ❤️ fail2ban

Paragone, (edited )

A couple of decades ago, iirc, SANS.org ( IF I’m remembering who it was who did it ) put a fresh-install of MS-Windows on a machine, & connected it to the internet.

It took SEVERAL MINUTES for it to be broken-into, & corrupted, botnetted.

The auto-attacks by botnets are continuous: hitting different ports, trying to break-in, automatically.

I’ve had linux desktops pwned from me.

the internet should be considered something like a mix of toxic & corrosive chemicals: “maybe” your hand will be fine, if you dip it in for a moment & immediately rinse it off ( for 3 hours ), but if you leave you limbs dwelling in the virulent slop, Bad Things™ are going to happen, sooner-or-later.

I used to de-infest Windows machines for my neighbours…

haven’t done it in years: they’ll not pay-for good anti-virus, they’ll not resist installing malware: therefore there is no point.

Let 'em rot.

I’ve got a life to work-on uncrippling, & too-little strength/time left.

“but I don’t need antivirus: i never get infected!!”

then how come I needed to de-infest it for you??

“but I don’t need an immune-system: pathogens are a hoax!!”

get AIDS, then, & don’t use anti-AIDS drugs, & see how “healthy” you are, 2 years in.

Same argument, different context-mapping.

Tarpit was a wonderful-looking invention, for Linux’s netfilter/iptables, years ago: don’t help botnets scan quickly & efficiently to help them find a way to break-in…

Anyways, just random thoughts from an old geek…

EDIT: “when do I need to wear a seatbelt?”

is essentially the same category of question.

_ /\ _

conorab,

Other comments have hit this, but one reason is simply to be an extra layer. You won’t always know what software is listening for connections. There are obvious ones like web servers, but less obvious ones like Skype. By rejecting all incoming traffic by default and only allowing things explicitly, you avoid the scenario where you leave something listening by accident.

wolf, (edited )

Seriously, unless you are extremely specialized and know exactly what you are doing, IMHO the answer is: Always (and even being extremely specialized, I would still enable a firewall. :-P)

Operating systems nowadays are extremely complex with a lot of moving parts. There are security relevant bugs in your network stack and in all applications that you are running. There might be open ports on your computer you did not even think about, and unless you are monitoring 24/7 your local open ports, you don’t know what is open.

First of all, you can never trust other devices on a network. There is no way to know, if they are compromised. You can also never trust the software running on your own computer - just look at CVEs, even without malicious intentions your software is not secure and never will be.

As soon as you are part of a network, your computer is exposed, doesn’t matter if desktop/laptop, and especially for attacking Linux there is a lot of drive by attacks happening 24/7.

Your needs for firewalls mostly depend on your threat model, but just disabling accepting incoming requests is trivial and increases your security by a great margin. Further, setting a rate limit for failed connection attempts for open ports like SSH if you use this services, is another big improvement for security. (… and of course disabling password authentication, YADA YADA)

That said, obviously security has to be seen in context, the only snake oil that I know of are virus scanners, but that’s another story.

People, which claim you don’t need a firewall make at least one of the following wrong assumptions:

  • Your software is secure - demonstrably wrong, as proven by CVEs
  • You know exactly what is running/reachable on your computer - this might be correct for very small specialized embedded systems, even for them one still must always assume security relevant bugs in software/hardware/drivers

Security is a game, and no usable system can be absolutely secure. With firewalls, you can (hopefully) increase the price for successful attacks, and that is important.

bushvin,

You may also want to check up on regulations and laws of your country.

In Belgium, for instance, I am responsible for any and all attacks originating from my PC. If you were hacked and said hackers used your computer to stage an attack, the burden of proof is upon you. So instead of hiring very expensive people to trace the real source of an attack originating from your own PC, enabling a firewall just makes sense, besides making it harder on hackers…

Kalcifer,
@Kalcifer@sh.itjust.works avatar

That’s a strange law. That’s like saying one should be held responsible for a thief stealing their car and then running over someone with it (well, perhaps an argument could be made for that, but I would disagree with it).

Kalcifer,
@Kalcifer@sh.itjust.works avatar

Seriously, unless you are extremely specialized and know exactly what you are doing, IMHO the answer is: Always

In what capacity, though? I see potential issues with both server firewals, and client firewalls. Unless one wants their devices to be offline, there will always be at least one open port (for example, inbound on a server, and outbound on a client) which can be used as an attack vector.

Atemu,
@Atemu@lemmy.ml avatar

#2 is strange – why does it matter?

It doesn’t. If you’re running a laptop with a local web server for development, you wouldn’t want other devices in i.e. the coffee shop WiFi to be able to connect to your (likely insecure) local web server, would you?

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?

Who is “they”? What about all the other ports?

Imagine a family member visits you and wants internet access in their Windows laptop, so you give them the WiFi password. Do you want that possibly malware infected thing poking around at ports other than 80 running on your server?

Obviously you shouldn’t have insecure things listening there in the fist place but you don’t always get to choose whether some thing you’re hosting is currently secure or not or may not care too much because it’s just on the local network and you didn’t expose it to the internet.
This is what defense in depth is about; making it less likely for something to happen or the attack less potent even if your primary protections have failed.

#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

Mostly addressed by the above but also note that you likely do have applications listening on ports you didn’t know about. Take a look at sudo ss -utpnl.

#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.

It’s rather the other way around; you don’t want the outside world to be able to talk to untrusted software on your computer. To be a classical “door”, the application must be able to listen to connections.

OTOH, smarter malware can of course be something like a door by requesting intrusion by itself, so outbound filtering is also something you should do with untrusted applications.

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?

I’d rather liken it to a razor fence around your house, protecting you from thieves even getting near it. Your windows are likely safe from intrusion but they’re known to be fragile. Razor fence can also be cut through but not everyone will have the skill or patience to do so.

If it turned out your window could easily be opened from the outside, you’d rather have razor fence in front until you can replace the window, would you?

Kalcifer,
@Kalcifer@sh.itjust.works avatar

If you’re running a laptop with a local web server for development, you wouldn’t want other devices in i.e. the coffee shop WiFi to be able to connect to your (likely insecure) local web server, would you?

This is a fair point that I hadn’t considered for the mobile use-case.

Imagine a family member visits you and wants internet access in their Windows laptop, so you give them the WiFi password. Do you want that possibly malware infected thing poking around at ports other than 80 running on your server?

Fair point!

note that you likely do have applications listening on ports you didn’t know about. Take a look at sudo ss -utpnl.

Interesting! In my case I have a number of sockets from spotify, and steam listening on port 0.0.0.0. I would assume, that these are only available to connections from the LAN?

It’s rather the other way around; you don’t want the outside world to be able to talk to untrusted software on your computer. To be a classical “door”, the application must be able to listen to connections.

OTOH, smarter malware can of course be something like a door by requesting intrusion by itself, so outbound filtering is also something you should do with untrusted applications.

It could also be malicious software that simply makes a request to a remote server – perhaps even siphoning your local data.

If it turned out your window could easily be opened from the outside, you’d rather have razor fence in front until you can replace the window, would you?

Fair point!

Atemu,
@Atemu@lemmy.ml avatar

In my case I have a number of sockets from spotify, and steam listening on port 0.0.0.0. I would assume, that these are only available to connections from the LAN?

That’s exactly the kind of thing I meant :)

These are likely for things like in-house streaming, LAN game downloads and remote music playing, so you may even want to consider explicitly allowing them through the firewall but they’re also potential security holes of applications running under your user that you have largely no control over.

  • All
  • Subscribed
  • Moderated
  • Favorites
  • •
  • linux@lemmy.ml
  • localhost
  • All magazines
    •
    Loading…
    Loading the web debug toolbar…
    Attempt #