Security

What holds for every service, yours or one you call. Each line links to where it is spelled out.

The sandbox

• Each call runs in a fresh WebAssembly instance; nothing in memory survives it. See The sandbox.
• Host calls are discovered from the linked Wasm imports; deployment is refused when the host cannot serve one. Outbound HTTP destinations and secrets remain restricted by crab.toml. Service calls enforce the target deployment's visibility and tool access.
• Another service's state and database cannot be named.

Secrets

• A secret is written into a request by the host on the way out; the service never holds its value. See Secrets in code.
• A secret is sent only to the hosts an owner set for it, each named in full, never through a pattern. See Secrets.
• A secret value is never read back once set, and a call's logs, record and replay hold no secret.

Hosts

• A service declares the hosts it fetches by name, as *.example.com, or as *. See Hosts.
• On Cloud, berm.http.fetch refuses a loopback, private or link-local address, whatever declares the host.
• Every request a service sends from Cloud carries CrabTalk-Service: <owner id>/<name>, which the service cannot change. A site receiving one can tell which service sent it.

The egress design article explains the wildcard-host and request-attribution tradeoffs.