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How to audit network as a noob? (discuss.tchncs.de)

submitted 2 weeks ago by Jean_le_Flambeur@discuss.tchncs.de to c/homelab@lemmy.ml

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Hey y'all, I have a small network with opnsense firewall, a unify ap, some client in different subnets, vpn, DNS and some servers.

As I am completely self thought, I got everything to run reading the docs and forums, but I have no idea how to test if what I build is safe and stable.

Are there good up to date tools, or checklists one could follow to audit the different parts of the network (most important the opnsense config)?

What do you check if looking for security issues?

The network mostly relies on client separation through different subnets on different vlans, but I fear I dont understand how for example the vpn and the nas work together in detail to be sure there is no security implication I oversee.

Also: how do you handle client authentication for devices on the same subnet? I know IP/mac-adress ARP entries are easily spoofed and therefore not secure, but I haven't seen how to do it correctly

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[–] hoodoo5x5@lemmy.world 4 points 2 weeks ago (1 children)

Honestly, OPNSense has some fairly decent reporting that can take you a fair ways. https://docs.opnsense.org/manual/reporting_traffic.html

Watching the traffic in those tools can highlight a lot of concerns. Is outbound wide open from all networks?

In general, I wouldn't recommend doing auth at the network layer. You could do radius, AD, or something similar if that's a concern. You could use Tailscale and create a mesh overlay - I'd do that before VPN. Going down this road can, of course, cause a lot of challenges with phones and other iot devices. I tend to keep the iot vlan barebones for that reason.

[–] Jean_le_Flambeur@discuss.tchncs.de 1 points 2 weeks ago

Okay, yeah i do look at the reporting to Register things that look off, but I am not sure I recognize everything that IS off.

Generally I keep outbound and inbound completely closed except for the connections I need, which I manually allow for in the rules for each subnet. for the client WiFi I have a alias with all private (ipv4) ranges, and a rule that allows outbound to anything but that (so only connections to "the internet" not to stuff in my network.

Radius is the thing I at least came across a few times in my settings, from what I understand I would need a dedicated radius server all can reach an authenticate against right? At the moment I only have a bare metal Debian server for the self hosted unifi controller, maybe I could learn proxmox and do radius and unifi in different VMs on that machine.

What would the tailscale option mean? I have heard about it (but mostly mentioned in combination with arr stacks, which I dont have, so I never looked at it. What does it do? What are the benefits over for example radius?

Okay, so radius/tailscale for client networks, for iot I rely on subnet separation would be your advice?

[–] HamsterRage@lemmy.ca 1 points 2 weeks ago (2 children)

Remember that separation by VLANs does very little unless you have firewall rules that limit traffic between them.

[–] Jean_le_Flambeur@discuss.tchncs.de 1 points 2 weeks ago

Well I have separate subnets for separate vlans. Connections between them get blocked by the firewall by default from my understanding, but to be safe I explicitly deny all outbound AND inbound connections, so I have to make a rule for each of two subnets if I want inter subnet communication, which is the case for the shared media server. If I do that I whitelist which IPs can reach which IPs on the different subnet. There still is the problem that different clients on the same network can "steal"the IP of other clients with more permissions. That's why I asked about authentication

[–] Blue_Morpho@lemmy.world 0 points 2 weeks ago (2 children)

I have argued that vlans do very little for home users.

Vlans with firewall rules mean that every room in your house has a rule that you have to go out the locked front door before going back into another room. But if an external threat can bypass the front lock, having a rule that everyone inside has to use the front lock does nothing. Either the front lock works in which case everything is safe or it doesn't work in which case the rule to use the front door lock every time you go from inside room to inside room does nothing.

[–] HamsterRage@lemmy.ca 2 points 2 weeks ago

Let's look at the recent case where the FBI/Google took down a sites related to a botnet that was using Android TV boxes that came equipped with malware. These were cheapo, third tier units probably sold via Temu or some equivalent.

In this case they were being used to relay and obfuscate crime related traffic, but there's no reason that the same technique couldn't be used to more directly attack the hosting network.

I think that if you assume that device that you plug into your network could be used as an edge router into your network for a WireGuard connection with the outside world, then isolating those devices from your homelab is a good idea.

Something like an Android TV box obviously needs to connect to the Internet, and there are good reasons that you might want to run a VPN on it too. So trying to limit its access to the Internet via ports would be difficult. A VLAN would give me some piece of mind here.

[–] Jean_le_Flambeur@discuss.tchncs.de 1 points 2 weeks ago

Yes, that's the idea, that everything needs to go through opnsense, where I manage who's allowed to go where. The question now is how to determine if the front door lock is safe, so that nothing can leak through because I misconfigured nat or VPN or something

[–] IsoKiero@sopuli.xyz 0 points 2 weeks ago (1 children)

Perhaps the easiest, and still at least decent, approach is to just run nmap (or any other port scanner) against your own subnets/IP addresses. That way you'll at least find out if the firewall allows something trough which it shouldn't, Also you can run tcpdump/wireshark on destination host to see if it receives packets it shouldn't.

For client authentication, if ARP filtering is not enough, you could set up 802.1x, but that's likely a massive overkill (and overhead) for home network. I personally don't authenticate clients separately. Just WPA2 on wifi and firewall rules to allow/deny traffic between subnets. Sure, it's pretty easy to bypass, but in practise you'd need to be inside the house to access some parts of the network. But my threat model is mostly about a handful of IOT things which I don't trust with full network access, not about someone unauthorized getting access to my home network.

[–] Jean_le_Flambeur@discuss.tchncs.de 2 points 2 weeks ago (1 children)

I tried that a little, but my problem was that there was to much stuff going on in the network for me to understand and review all. I am currently not reachable at all from the big internet, only local server access and I only get working connections if I rset an IP corresponding to the vlan I am in, but unify broadcasting, Nat, VPN, etc. Make a lot of connections and connection attempts internally I dont understand.

Problem with no client authentication is that the network is used by multiple separate households not necessary trusting each other, and some now want to host servers to the public, which would mean lots of untrusted traffic. I am concerned if they dont handle their security right and have access to for example our shared media server, they could scrape ip-mac address pairs to get deeper in the network. Any thoughts on benefits and lows of 802.1 vs. Radius?

[–] IsoKiero@sopuli.xyz 2 points 2 weeks ago

Radius is a part of 802.1x standard and for your threat model that does absolutely nothing. If a bad actor can access a device already in your network, then network level authentication doesn't do anything. For example it prevents from someone randomly plugging their device in your switch and getting access that way, or it only allows verified clients to your WLAN. But once the network connectivity is already established you need a totally different tools.

Mainly that means firewall on your network and/or servers. There's multiple ways to build that. You could get a separate firewall device to block access from the rest of the network to your devices or you can set up firewall for each of your things separately. All solutions have their own pros and cons and 'correct' solution depends on multiple variables.