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feat(web): enforce localhost-only binding; expand loopback origin allow-list (#1796)

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Closes #1795.

Enforce localhost-only binding in code (the "never 0.0.0.0" rule was only a spec note): refuse an all-interfaces HOST — across every spelling the OS binds as the wildcard (inet_aton decimal/octal/hex, IPv6, IPv4-mapped, zone-scoped, IDNA/Unicode) — unless DANGEROUSLY_BIND_ALL_INTERFACES=true (Docker's sanctioned opt-in). Fixes the reported stdio-connect 403 by expanding the default loopback origin allow-list to all three interchangeable forms.

Hardening surfaced across an extended review: closes an IDNA/fullwidth wildcard bypass, a blank-ALLOWED_ORIGINS fail-open, and the CLI/TUI OAuth-callback wildcard bind (loopback-only now, RFC 8252); canonicalizes the origin allow-list the way a browser does; derives frame-ancestors from the real embedder list (IPv6-literal exclusion verified in headless Chromium); strictPort on all three bind points; and preserves the CLI exit-code map + JSON envelope through the mcp-inspector --cli launcher path. Shared host normalization lives in core/node/hostUrl.ts. Docs + tests + smokes throughout.

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Cliff Hall 2026-07-26 22:15:10 -04:00 • committed by GitHub
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@ -25,8 +25,11 @@ COPY --from=builder /build/modelcontextprotocol-inspector-*.tgz /tmp/inspector.t
RUN npm install -g /tmp/inspector.tgz && rm /tmp/inspector.tgz
# Serve on all interfaces so the UI is reachable from outside the container, and
# never try to open a browser from inside it.
# never try to open a browser from inside it. Binding 0.0.0.0 is refused by
# default (it exposes the process-spawning backend to the network); a container
# is the sanctioned exception, so opt in explicitly via DANGEROUSLY_BIND_ALL_INTERFACES.
ENV HOST=0.0.0.0 \
DANGEROUSLY_BIND_ALL_INTERFACES=true \
CLIENT_PORT=6274 \
MCP_AUTO_OPEN_ENABLED=false
EXPOSE 6274