Clauster: Non-loopback deployments can serve the dashboard unauthenticated when auth.enabled is unset

Summary

A Clauster instance bound to a non-loopback address (e.g. 0.0.0.0 or a LAN IP) can serve the entire dashboard and its API without any authentication — even when the operator has configured a password — if auth.enabled is left at its default (false). The operator believes the instance is password-protected; in reality every request is served unauthenticated.

Impact

An unauthenticated attacker with network access to the instance gains full control of the dashboard: list projects, spawn/stop claude remote-control bridges in any project directory, edit CLAUDE.md, read bridge logs, and (where configured) clone repositories. Because bridges run Claude Code against the host's project directories, this is effectively remote code execution in those projects.

Loopback (127.0.0.1) deployments need no auth by design and are not affected.

Affected configurations

All released versions (≤ 0.2.1) where all of the following hold:

• host is a non-loopback address, and
• auth.password_required: true and/or auth.reverse_proxy.enabled: true is set, and
• auth.enabled is left at its default false.

Docker deployments are affected: the image binds 0.0.0.0, and the previously-documented docker run command did not set auth.enabled.

Root cause

Two layers checked different flags:

• The runtime auth guard enforces authentication only when config.auth.enabled is true; when false it passes every request through unauthenticated.
• The config validator, for a non-loopback bind, required only one of auth.password_required / auth.reverse_proxy.enabled / auth.allow_unauthenticated_network — not auth.enabled. So a config with a password but enabled=false validated, started, and enforced nothing.

Proof of concept

With host: 0.0.0.0, auth.password_required: true, a valid auth.password_hash, and auth.enabled unset:

curl http://<host>:7621/api/instances

returns 200 with the full instance list and no credentials. Setting auth.enabled: true returns 401.

Patches

An upcoming patch release makes the config validator fail closed: a non-loopback bind is refused unless authentication is actually enforced — auth.enabled: true together with auth.password_required (+ a hash) or auth.reverse_proxy.enabled, or the explicit auth.allow_unauthenticated_network opt-out. The README, clauster.yml.example, and Docker docs were corrected to match.

Workaround

On any non-loopback deployment, set auth.enabled: true in clauster.yml (or CLAUSTER_AUTH_ENABLED=true) alongside your existing auth.password_required + hash (or reverse-proxy) settings. Alternatively, bind to loopback only and reach it via an SSH tunnel or a trusted authenticating reverse proxy.

Credit

Found during an internal security review.