How do I host Jellyfin in the most secure manner possible?

Please take this discussion to this post: https://lemmy.ml/post/28376589

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After reviewing the entire thread, I have to say that this is quite an interesting question. In a departure from most other people's threat models, your LAN is not considered trusted. In addition, you're seeking a solution that minimizes subscription costs, yet you already have a VPN provider, one which has a -- IMO, illogical -- paid tier to allow LAN access. In my book, paying more money for a basic feature is akin to hostage-taking. But I digress.
The hard requirement to avoid self-signed certificates is understandable, although I would be of the opinion that Jellyfin clients that use pinned root certificates are faulty, if they do not have an option to manage those pinned certificates to add a new one. Such certificate pinning only makes sense when the client knows that it would only connect to a known, finite list of domains, and thus is out-of-place for Jellyfin, as it might have to connect to new servers in future. For the most part, the OS root certificates can generally be relied upon, unless even the OS is not trusted.
A domain name is highly advised, even for internal use, as you can always issue subdomains for different logical network groupings. Or maybe even ask a friend for a subdomain delegation off of their domain. As you've found, without a domain, TLS certificates can't be issued and that closes off the easy way to enable HTTPS for use on your untrusted LAN.
But supposing you absolutely do not want to tack on additional costs, then the only solution I see that remains is to set up a private VPN network, one which only connects your trusted devices. This would be secure when on your untrusted LAN, but would be unavailable when away from home. So when you're out and about, you might still need a commercial VPN provider. What I wouldn't recommend is to nest your private VPN inside of the commercial VPN; the performance is likely abysmal.
- But supposing you absolutely do not want to tack on additional costs, then the only solution I see that remains is to set up a private VPN network, one which only connects your trusted devices. This would be secure when on your I trusted LAN, but would be unavailable when awat from home.
  Traditionally this would be performed by creating a dedicated network of trusted devices. Most commonly via a VLAN for ease of configuration. Set the switch ports that the trusted devices are connected to to use that vlan and badabing badaboom you're there. For external access using Tailscale or one of the many similar services/solutions (such as headscale, netbird, etc.) with either the client on every device or using subnet routing features to access your trusted network, and of course configure firewalls as desired
  
  I had a small typo where "untrusted" was written as "I trusted". That said, I think we're suggesting different strategies to address OP's quandary, and either (or both!) would be valid.
  My suggestion was for encrypted L3 tunneling between end-devices which are trusted, so that even an untrustworthy L2 network would present no issue. With technologies like WireGuard, this isn't too hard to do for mobile phone clients, and it's well supported for Linux clients.
  If I understand your suggestion, it is to improve the LAN so that it can be trusted, by way of segmentation into VLANs which separate the trusted devices from the rest. The problem I see with this is that per-port VLANs alone do not address the possibility of physical wire-tapping, which I presumed was why OP does not trust their own LAN. Perhaps they're running cable through a space shared with other tenants, or something like that. VLANs help, but MACsec encryption on the wire paired with 802.1x device certificate for authentication is the gold standard for L2 security.
  But seeing as that's primarily the domain of enterprise switches, the L3 solution in software using WireGuard or other tunneling technologies seems more reasonable. That said, the principle of Defense In Depth means both should be considered.
  
  Physical wire tapping would be mostly mitigated by setting every port on the switch to be a physical vlan, especially if the switch does the VLAN routing. Sure someone could splice an ethernet cable, which would really only be mitigated by 802.1x like you already said, but every part of this threat model makes zero sense. You ultimately have to trust something (and apparently in OP's case that's a third party VPN provider that charges extra to not block LAN access while connected and they remain entirely on the free tier of)
  But at the very least, not trusting everything on the network is a very enterprise kind of threat model, so using standard enterprise practices of network segmentation, firewalling, and potentially MAC-binding and 802.1x if so desired isn't a bad idea, if for no other reason than it might lead to a career in network administration. And honestly I mostly want to get OP to not think of VPNs like a magical silver bullet and see what other tools exist in the toolbox
  
  Physical wire tapping would be mostly mitigated by setting every port on the switch to be a physical vlan
  Can you clarify on this point? I'm not sure what a "physical VLAN" would be. Is that like only handling tagged traffic?
  I'm otherwise in total agreement that the threat model is certainly not typical. But I can imagine a scenario like a college dorm where the L2 network is owned by a university, and thus considered "hostile" to OP somehow. OP presented their requirements, so good advice has to at least try to come up with solutions within those parameters.
  
  Y'know what that was terrible writing on my part. Where I put "physical vlan" I just meant specifying each port be a specific vlan rather than a trunk port that has multiple clans on in
  I should probably proofread more and write less when tired

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