The session callbackUrl becomes a server-side fetch target in
api.save-to-journal (POSTed with the callback bearer token, and the
journal's response is reflected to the caller). The /new query-param
loader already validated it, but the programmatic POST /api/sessions
entry point — anonymous, since the Planner is stateless — stored it
unvalidated. An attacker could make the Planner backend POST to
arbitrary hosts, including 169.254.169.254 and other internal targets.
- validateFetchUrl now blocks private / loopback / link-local /
CGNAT / cloud-metadata hosts (IPv4, IPv6, IPv4-mapped) when an
explicit allowlist isn't set. Gated on NODE_ENV=production && !E2E
(the requireSecret idiom) so the dev/e2e journal-on-localhost save
flow is unaffected. An explicit PLANNER_CALLBACK_ALLOWED_HOSTS still
takes precedence and remains the full-closure control (it also stops
DNS-name-to-private rebinding, which literal blocking does not).
- POST /api/sessions now validates callbackUrl exactly as /new does.
- api.save-to-journal re-validates immediately before the fetch
(defense in depth: covers sessions persisted before this change and
narrows the create→save rebinding window).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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