has_access_to_file() derives file access from the objects a file is attached to
(knowledge bases, workspace models). Those branches returned True for any access_type
whenever the user held that permission on the object, write/delete included. Since a
user can create their own KB or model and attach any file they can merely READ (KB
attach and the model meta.knowledge validator both gate on read access only), a user
with read access to a victim file could launder it into write/delete: attach it to an
object they own, then rename, overwrite or delete it via the write-gated file routes
(POST /files/{id}/rename, /data/content/update, DELETE /files/{id}). This is the
residual of GHSA-vjqm-6gcc-62cr (CVE-2026-54012) left open by the read-only attach
validator (CWE-863).
An object now confers write/delete on a file only when the object's owner owns that
file, so delegation originates from the file's own owner. Read is unchanged (RAG and
shared-object reads still work), and legitimate delegation is preserved: a write grant
on an object whose owner owns the attached file still confers write. Applied to all
three object branches: knowledge base, file home collection, and workspace model.
Co-authored-by: rexpository <30176934+rexpository@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
