Local and LAN security

Français · Type: explanation + reference · Audience: author · Context: local Studio · Status: ready · Applies from: 4.2.1

The local Studio · contract: stable · verified by CI (support matrix of 4.4.0, 2026-10-23): Chromium end to end (the Studio's checks); Windows: the unit suite only · automated checks: jobs e2e, windows; CI plan e2e, windows; 2 test files · people's passes: studio-hero-matrix not run (#238) · known limits: lan-is-not-public

The local Studio writes files on your machine and can call a model provider with your key. This page says what protects those routes, on your own machine and on your local network, and where the protection stops.

Why

A dev server that writes files is a door into your machine. Three things could knock on it: another machine on the network, a web page in your browser that tries to reach localhost (directly, or by rebinding its own name to your machine, "DNS rebinding"), and a model provider address that would lead the Studio to a service of your private network ("SSRF"). The Studio closes each one by default and opens only what you ask for.

Local and LAN

• Loopback by default. npm run studio and npm run dev listen on 127.0.0.1 (port 5173): another machine cannot reach their file-writing routes.
• Its own names only. Every Studio, asset, layout and assistant route answers only to the names of this machine (localhost, 127.0.0.1, [::1]), and in LAN mode to the addresses studio:lan serves. A page on another site that rebinds its name to your machine sends that name as Host: refused (403), even with a matching Origin.
• Same origin. A request that carries an Origin must come from the Studio's own origin (403 otherwise). A write (anything but GET, HEAD and OPTIONS) without an Origin header is refused (403): a script must send one.
• LAN mode, behind a token. To work from a phone, npm run studio:lan (or npm run dev:lan) listens on the network and prints a fresh capability token, drawn at each start (24 random bytes), unless you set WEB_SCUMM_STUDIO_TOKEN yourself. Every Studio, asset, layout and assistant route then requires that token, as the x-web-scumm-token header, the ?token= parameter of the printed URL, or the cookie the URL sets (web_scumm_studio, HttpOnly, SameSite=Strict). The host names allowed are the machine's IPv4 network addresses (WEB_SCUMM_STUDIO_HOSTS, set by the command).
• Never on the Internet. Do not expose the development port to the Internet: the token protects a session on your network, not a public server. To put a Studio online, use the hosted Studio (What runs where).

Guarantee · lan-token-same-origin · referenced · executed on aff6caab7514 · scope self-checked by the author (AI), not reviewed In LAN mode the Studio answers 401 to a request without the session's token, and 403 to a write whose Origin is another site, even with the token.

Guarantee · own-names-only · referenced · executed on aff6caab7514 · scope self-checked by the author (AI), not reviewed A Host that is not this machine (or an address studio:lan serves) is refused, even with a matching Origin.

Model providers

• Keys stay in the browser tab (sessionStorage) and go with each request; the relay keeps a key in memory for that request only, never on disk, never in a log (The Assistant).
• Addresses. Arbitrary provider URLs are disabled unless WEB_SCUMM_ALLOW_CUSTOM_PROVIDER=1. Even then, private and link-local destinations stay blocked, except the explicit local Ollama preset, in both IP families: loopback (127.0.0.0/8, [::1]), unspecified (0.0.0.0, ::), private (10/8, 172.16/12, 192.168/16, 100.64/10, fc00::/7), link-local (169.254/16, fe80::/10), IPv4-mapped IPv6, and the names localhost, *.localhost, *.local, *.internal. A custom provider must use HTTPS.
• Calls. A provider call never follows a redirect, gives up after 60 s, and reads at most 8 MB of answer.

What is not protected: the game is trusted code

A game's TypeScript and its custom commands are trusted code, not sandboxed data: the Studio, the validator and the solver run them on your machine. Open only games you trust, as you would any project you npm install. See SECURITY.md.

Limit · lan-is-not-public The LAN token is a convenience for a phone on your own network: it is shown in the terminal and in the URL, and lives as long as the server. It is not an authentication for a public deployment.

Alternatives set aside

• Listening on every interface by default: convenient for phones, but it would put the file-writing routes on every network the laptop joins. LAN mode is an explicit command.
• A password: a token drawn per session needs nothing to remember and dies with the server.
• Allowing any provider URL: one setting away (WEB_SCUMM_ALLOW_CUSTOM_PROVIDER=1), but a URL typed in a page must never reach your private network.

Trade-offs

• A script that writes through the Studio's API must send an Origin header matching the Studio, and in LAN mode the token.
• A phone needs the URL with the token once; the cookie keeps it for the session.

Decisions and ADRs

• Sources: tools/studio/security.ts, tools/serve-args.ts, tools/studio/assistant.ts, vite.config.ts.
• The variables: WEB_SCUMM_STUDIO_TOKEN, WEB_SCUMM_STUDIO_HOSTS, WEB_SCUMM_LAN, WEB_SCUMM_ALLOW_CUSTOM_PROVIDER.
• When a route refuses: Studio troubleshooting.

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