Fetch-Metadata and Origin are only attached to trustworthy destinations, so
over plain HTTP a rebound page's same-origin GET (EventSource, images,
navigations) arrives with no browser markers and a readable response. Remove
the marker shortcut; non-browser clients pass the same fence via loopback,
the CLI-derived LAN IP literals, or a declared authority.
A dangling colon (harness.internal:) or zero-padded port parses cleanly while
WHATWG silently rewrites it, turning an intended exact-port grant into an
any-port grant. Replace the character blacklist with a round-trip check: an
entry must read back from parsing exactly as written (case aside), refusing
the whole rewrite class at load.
WHATWG parsing would quietly read a hostname out of harness.internal/path or
user@harness.internal, authorizing the typo's hostname; other typos would sit
silently ignored until requests 403. Refuse every URL part beyond host[:port]
at plugin load.
Markerless requests pass on any Host (a non-browser sender is the principal
and forges headers anyway); browser Host matching gains port-less entries and
WHATWG normalization; dsh derives LAN IP-literal authorities for an
all-interfaces bind and web grows --trusted-host for named ones.
The only browser-trust guard covered host.pickDirectory, while the
consequential methods (session.prompt drives bash) accepted any Host —
open to DNS rebinding, where a rebound page reads and writes the API as
if same-origin and only the Host header betrays the attacker's domain.
The pickDirectory-specific loopback guard becomes a prefix-wide fence:
Host must be loopback or an exact host[:port] from the new trustedHosts
config, an attached Origin must equal that authority, and explicit
cross-site markers are refused; requests without browser markers (curl,
tests, native clients) pass, because without a browser there is no
confused deputy. The loopback-socket check is dropped — binding policy
expresses reachability, and the fence is not an auth layer. The Agent
Note records the full threat model and the alternatives.
