The client sends the "current page" as { id, title } in the request body and the
server echoed BOTH verbatim into the system prompt context and the
getCurrentPage tool. id and title are independently attacker/desync-controllable
(two tabs, stale navigation), so openPage.id could point at page B while
openPage.title said "Page A" — the model then reported "updated Page A" while it
actually edited page B (CASL still allowed it; the user has access). Red-team
finding #4.
Resolve the open page ONCE against the DB via a new `resolveOpenPageContext`:
workspace-scoped lookup + access check, returning the AUTHORITATIVE { id, title }
(title from the DB row, never the client) or null (fail-closed) for a missing /
foreign / inaccessible page. That validated value now feeds the system prompt,
the getCurrentPage tool, AND the new-chat history origin (which previously did
this validation inline, for the id only — now shared, and the title is fixed
too).
Tests: resolveOpenPageContext covers no-id, not-found, foreign-workspace,
Forbidden, non-Forbidden-fault (fail-closed), the DB-title-wins-over-client case,
and null-title coercion.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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