Braindance has no authentication. Whoever can reach the port can arm the recorder, start and stop a take, read the library, and delete footage. There are no accounts, no tokens and no TLS. It is a tool for driving a sensor on a network you control, and reaching it is the permission.

The bind address. The server listens on 127.0.0.1 unless you pass --host, so by default nothing off the machine can reach it. It prints on stdout when you widen the bind.

The origin rule, which only speaks to browsers. A request carrying an Origin header must be same-origin, and a mutating HTTP route also requires a matching method and a JSON content type. A page you merely visit cannot produce those together. A request with no Origin skips the origin check, because every call across the capture-node link is a server-side fetch and Node has no origin to declare. So the rule stops hostile web pages and nothing else: curl, a script, or another machine on the Wi-Fi sends no Origin and is allowed everything.

A browser's Host must be an IP literal, localhost or a .local name. Comparing Origin against Host alone does not survive DNS rebinding: a name the attacker controls, re-resolved onto the address you listen on, makes the two strings equal, and binding to loopback does not prevent it because the browser doing the connecting is on the machine. node tools/guard-check.mjs proves the rule, and --mutate host-accepts-a-name must fail.

A browser sending an Origin from any other hostname, such as a reverse proxy, an /etc/hosts entry or a Tailscale MagicDNS name, is refused on every guarded route. Reach the server by address instead.

Everything, to everyone who can route to the port:

The origin rule covers /camera.mjpg as it covers the mutating routes, and it buys only that a browser declaring a foreign origin is refused. An <img> tag, curl, ffmpeg, VLC and another machine send no origin and are not stopped. Treat the route as public to the network you bound to.

POST /library/reveal/:id does not widen with the bind. It starts the platform's file manager on a take's path, and it refuses any caller whose socket is not loopback, read off remoteAddress. The id is held to VALID_ID, the path must be a direct child of the captures directory, the program is a fixed string per platform, and the arguments are an array with no shell between them. --reveal-with substitutes the program for a proof tool and is never passed on an operator's machine.

• Leave the default bind alone on any machine you edit on. It needs no network access.
• Pass --host 0.0.0.0 only on a capture node, on a network you control. Conference or hotel Wi-Fi is not that. A wired link or a dedicated access point between node and editing machine is.
• Put it behind an SSH tunnel or a WireGuard link if it must cross a network you do not control, with the server still bound to loopback on the far side. A tunnelled browser counts as local: it gets the uncapped monitor rate and is offered Show in Finder, which opens a window on the host. Whoever built the tunnel authenticated to the host, so treat tunnel access as sitting at the machine.
• Nothing here is safe to expose to the internet. Not behind a reverse proxy, not on a forwarded port.

Open an issue, or mail tim@timkraus.eu for anything you would rather not file in public. There is no bounty and no SLA. Say whether you found it by reading or by running it.

These writes use the route table's same-origin and JSON guards. The CLI sends HTTP requests without an Origin header. Network reachability grants control; keep the default loopback bind or use the authenticated tunnel described above.