CVE-2026-71317: Lemur: Sub-CA creation never checks `AuthorityPermission` on the parent authority

Repo under test: https://github.com/Netflix/lemur

When ADMIN_ONLY_AUTHORITY_CREATION=False (an explicitly supported and documented configuration), POST /api/1/authorities with type=subca never verifies that the caller holds AuthorityPermission on the supplied parent authority. The parent field is resolved by AssociatedAuthoritySchema via a raw fetch_objects(Authority, data) lookup, then passed straight through service.create → mint → cryptography-issuer.create_authority, which loads options["parent"].authority_certificate.private_key and signs a brand-new intermediate CA on the caller’s behalf.

Any authenticated non-read-only user can therefore mint a sub-CA chained to any internal root whose private key Lemur holds — including roots they hold no role on — attach a role they already belong to, and immediately issue or offline-sign trusted leaf certificates for arbitrary names.