Security Fix
78bfc5b408
Caddy fronted the Hub at http://sovransystemsos.local, but the Hub already listens on 0.0.0.0:8937 itself, and nothing Caddy added is something it needs: - Not the name. That is avahi's: mDNS advertises a hostname, not a port, so the name resolves wherever the Hub listens. - Not TLS (the site was plain http), not authentication, not cache headers. The header block duplicated NoCacheMiddleware, and its Clear-Site-Data ("cache") overrode the app's stronger ("cache", "storage"). - Not access control, and this is the point. With ports 80/443 forwarded for public services, a Host header on those ports reached the Hub. That second door is how the reported bug happened, andc33457fguards it with an address check instead of closing it. The Hub is now served on port 8937 only, at http://sovransystemsos.local:8937, and Caddy has no site for it. The only thing Caddy answers on 80/443 is the public sites. Caddy keeps Ride The Lightning (:3051) and Mempool (:60847), because those do need it: Sovran_Bitcoin binds both to 127.0.0.1 and RTL's unit is sandboxed to loopback besides, so Caddy is how the local network reaches them. - caddy.nix: no Hub site. Caddy runs wherever RTL and Mempool do, which includes Bitcoin Node Only. There it did not run at all (enable was needsHttpsPorts || extraVhosts != ""), so :3051 and :60847 were open in the firewall with nothing listening. Ports 80/443 still follow needsHttpsPorts alone, so Node Only does not open them. The two sites are written only where their service exists; they were unconditional. - sovran-hub.nix: 8937 follows the new hub.directPort, 60847 follows Mempool. It used to be `[ 8937 60847 ]` on every role, Desktop Only included. - roles.nix: hub.directPort defaults to !roles.desktop: open on Server + Desktop and Bitcoin Node Only, closed on Desktop Only, where the Hub is reached from the machine itself through the desktop window on localhost. - The bind stays 0.0.0.0, which is IPv4 only: with that bind [::1]:8937 is refused and "localhost" falls back to 127.0.0.1. That is on purpose and is now said in the comment. An IPv6 listener would let in clients whose global addresses the Hub cannot tell from a stranger's, which is the question the previous commit declines to answer by guessing. - README, SECURITY.md and two strings in index.html give the new URL. Behaviour changes: the Hub's address gains :8937, and http://sovransystemsos.local on port 80 no longer reaches it. Bitcoin Node Only now runs Caddy. Evaluated with nix eval (nixpkgs as flake.lock pins it, Sovran_Bitcoin at the locked revision), firewall TCP ports per role:c33457fthis commit Server + Desktop 22 80 443 3051 8937 60847 22 80 443 3051 8937 Bitcoin Node Only 22 3051 8937 60847 22 3051 8937 60847 (Caddy now runs) Desktop Only 22 8937 60847 22 Port 22 is open on every role although sshd listens on loopback only; the last commit of this series deals with that. The Caddyfile the module really generates (the evaluated generator script, run, then `caddy validate` with Caddy 2.9.1): Node Only gets the two sites and nothing else; Server + Desktop with every domain configured gets the seven domain sites plus :3051 and :60847 and no mention of the Hub; with Bitcoin off there are no local-network sites; Node Only with Bitcoin off and no domains leaves Caddy off. Add tests/test_hub_direct.py and keep tests/test_caddy_lan_only.py for the two sites it still covers.
7.2 KiB
Security Policy
Supported versions
| Release | Supported |
|---|---|
| Latest stable release | Yes |
main / staging-dev |
Development only |
Older than 1.0.0 |
No |
Install the newest stable point release to receive security fixes.
Report a vulnerability
Do not open a public issue or pull request. Report privately through:
Include the affected version, impact, reproduction steps, and a minimal proof of concept. Never send wallet recovery words, private keys, or live credentials.
We aim to acknowledge reports within two business days. Please allow reasonable time for a fix and coordinated disclosure.
Security model
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 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, 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.
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.
sovran_systemsOS.hub.directPort = true in custom.nix opens port 8937 if you
do 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;
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.
Caddy serves Ride The Lightning (port 3051) and Mempool (port 60847) only to this computer and to clients on your local network (private, link-local, and VPN addresses), even when ports 80 and 443 are forwarded to this computer for public services. Other IPv4 clients get the connection closed. IPv6 global addresses are not filtered.
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 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 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
Sovran_Bitcoin repository
and consumed as a flake input. OS-specific customizations (Second_Drive paths,
operator user, Hub integration) are bridged by
modules/sovran-bitcoin-integration.nix. The nix-bitcoin.* option namespace
and /etc/nix-bitcoin-secrets path remain only for upgrade compatibility.
Supply chain and integrity
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.
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.
Access and service isolation
- Firewall enabled by default
- Public SSH and remote desktop disabled by default
- Separate service users and systemd sandboxing where supported
- Administrative service ports bound to loopback where practical
- Tor enforced for supported Bitcoin traffic and onion services
- Public web services exposed only when enabled by the operator (this makes your home IP address public)
Tor reduces network exposure for configured Bitcoin services. It is not a guarantee against every IP leak, application bug, or traffic-analysis attack.
Restricted support access
Support uses a per-session SSH key on the non-root sovran-support account.
Sessions expire after 24 hours and have a small allowlist of sudo commands.
Wallet paths receive deny ACLs unless the operator explicitly removes them.
Disabling support removes the key and reapplies the ACLs.
Support events are written to /var/log/sovran-support-audit.log. This is a
local audit log, not a cryptographically tamper-evident record.
Out of scope
Sovran_SystemsOS cannot protect against:
- Compromised root or administrator credentials
- Stolen recovery words, private keys, or backups
- Malicious or compromised hardware, firmware, or build infrastructure
- Services the operator deliberately exposes or weakens
- Physical access without appropriate disk and firmware protections
Operator basics
- Verify downloads and stop if the checksum does not match.
- Apply stable security updates promptly.
- Use unique passwords and keep SSH/RDP off when not needed.
- Prefer a well-reviewed hardware signer for meaningful Bitcoin balances.
- Keep tested, offline backups in separate secure locations.
- Never share recovery words or private keys with support.
- Disable support access when the session ends and review the audit log.
No software can provide absolute security. Review your configuration and threat model before storing important funds or data.