v144 · security

Local network access restrictions for WebTransport

Restricts the ability to make requests to the user's local network using WebTransport, gated behind a permission prompt. A local network request is any request from a public website to a local IP address or loopback, or from a local website (e.g. intranet) to loopback. Gating the ability for websites to perform these requests behind a permission reduces t

concepts

  1. WebTransport LNA

    Local Network Access permission now gates WebTransport connections to private/loopback addresses, matching the existing fetch behaviour.

  2. LNA Permission Flow

    Try to open a WebTransport session to a private-network host and observe the LNA permission gate. The connection fails before any packet leaves the browser if the prompt is denied.

  3. Address Classifier

    Pick an origin URL and a target URL — the classifier names the address space of each, prints the verdict (allowed / prompt / blocked), and shows the full 3×3 policy matrix.

  4. Attack Scenario

    Step through the exact attack being mitigated: a public webpage silently probing a home router via WebTransport. Animated flow with LNA blocking applied, vs the legitimate case where a local app connects to a local device.

why it shipped

Local WebTransport connections are subject to many of the same attacks that the original LNA proposal are designed to solve.

references