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Revise SECURITY.md for clarity on Hub operations

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Updated security model details for Hub operation and access control.
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Sovran Systems
2026-10-02 11:35:53 -05:00
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SECURITY.md
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@@ -27,68 +27,37 @@ time for a fix and coordinated disclosure.
### Local-first operation
The Hub and core data run on operator-owned hardware. The Hub is intended for a
trusted local network and must not be port-forwarded to the internet. Public
services, DDNS, software updates, and optional third-party relays require
external networks and are outside a “fully offline” model.
The Hub and core data run on operator-owned hardware. The Hub is for a trusted
local network and must not be port-forwarded to the internet. It uses HTTP, so
authentication does not encrypt local network traffic.
The local Hub currently uses HTTP. Authentication does not encrypt local network
traffic, so use a trusted LAN and avoid public or guest Wi-Fi.
The Hub is served on port 8937 and is not fronted by Caddy.
The Hub is served on port 8937, on its own: Caddy does not front it. Server +
Desktop and Bitcoin Node Only open that port in the firewall, so other devices
on your local network reach the Hub at `http://sovransystemsos.local:8937`.
Forwarding ports 80 and 443 for public services does not put the Hub in front of
the internet, because the only thing Caddy answers on those ports is the public
sites.
Server + Desktop and Bitcoin Node Only (when BTCpayserver and/or LNURL is enabled) open that port in the firewall, so local devices reach the Hubat `http://sovransystemsos.local:8937`.
On Desktop Only the Hub is not published at all: reachable only from the machine itself, on localhost, with no TCP port
open in the firewall (UDP 5353 for mDNS only).
On Desktop Only the Hub is not published at all. It is reachable only from the
machine itself, through the desktop application window on localhost. Desktop
Only is the role most likely to be used away from home, and a root-capable admin
UI has no business listening on a coffee-shop network. The firewall there opens
no TCP port at all; the only port open is UDP 5353, for mDNS.
`sovran_systemsOS.hub.directPort = true` in `custom.nix` opens port 8937 if you
do want to reach a Desktop Only Hub from another device.
want to reach a Desktop Only Hub from another device.
The Hub also checks every client itself, before it shows a login page. It runs
as root, so it answers only this computer and the local network (loopback,
private, VPN and link-local addresses) and turns everyone else away, however
they reached it. The Hub listens on IPv4 only, so IPv6 clients do not reach it
at all; if that ever changes, global IPv6 addresses would be turned away,
because a laptop on your network and a stranger on the internet look the same
by address alone. If your devices use addresses outside the local ranges, list
their networks in `sovran_systemsOS.hub.extraLanNetworks` in `custom.nix`;
The Hub checks every client before showing a login page. It runs as root, so it
answers only loopback, private, VPN and link-local addresses and turns everyone
else away. The check goes by the address a connection comes from, so it is a
second lock and not a reason to forward port 8937: don't. Addresses outside the
local ranges go in `sovran_systemsOS.hub.extraLanNetworks` in `custom.nix`;
`sovran_systemsOS.hub.lanOnly = false` turns the check off.
The check goes by the address a connection comes from. A router that rewrites
that address when it forwards a port makes an outsider look local, so the check
is a second lock and not a reason to forward port 8937: don't.
Ride The Lightning (port 3051) and Mempool (port 60847) listen on loopback only,
and Caddy is how your local network reaches them. Caddy does not filter them by
client address: forwarding ports 80 and 443 for public services does not reach
them, because they answer on ports of their own, which nothing asks you to
forward. Do not forward 3051 or 60847. If you do, Ride The Lightning still asks
for its own random password and locks out repeated failures, and Mempool shows
public blockchain data, but neither should face the internet.
### Public services and your home IP address
Server + Desktop publishes services under your own domain. The Dynamic DNS
record at Njal.la then points at your home's public IP address, which anyone
can look up (domain privacy does not hide it), and ports 80 and 443 are open
to the whole internet. Public HTTPS certificates also list your service
Publishing public services on Server + Desktop points a DDNS record at your
home's public IP address, which anyone can look up, and lists your service
hostnames in Certificate Transparency logs. Desktop publishes nothing. Node
publishes nothing unless *Put BTCPay Server Online* or *Lightning Wallet
Connections* is on. See
[Server + Desktop and your home IP address](README.md#server--desktop-and-your-home-ip-address)
for what this means and the alternatives.
Sovran_SystemsOS does not ask a STUN server, public DNS resolver, or “what is
my IP” service for your address. The DDNS update asks Njal.la to use the
address the request came from, and the address Njal.la reports back is the one
Element calling and the Hub use.
### Bitcoin stack
Bitcoin and Lightning modules are maintained in the standalone
@@ -102,14 +71,11 @@ and `/etc/nix-bitcoin-secrets` path remain only for upgrade compatibility.
`flake.lock` pins flake inputs, and fetched source archives use fixed hashes.
Builds still depend on pinned Nixpkgs, NixVim, btc-clients-nix, upstream source
archives, and any configured binary cache. Keeping the Bitcoin modules in this
repository reduces an external dependency; it does not remove supply-chain
risk.
archives, and any configured binary cache.
The Hub integrity check verifies Nix store contents and compares the running
system with a build from local `/etc/nixos`. It does not authenticate the release
publisher or protect against an attacker who already controls root and can
change both the system and local configuration.
The Hub integrity check verifies Nix store contents against a build from local
`/etc/nixos`. It does not authenticate the release publisher or protect against
an attacker who already controls root.
### Access and service isolation