CVE-2026-42809: Apache Polaris: staged table creation could vend storage credentials for unvalidated locations

Apache Polaris can issue broad temporary ("vended") storage credentials during staged table creation before the effective table location has been validated or durably reserved. Those temporary credentials are meant to limit the scope of accessible table data and metadata, but this scope limitation becomes attacker- directed because the attacker can choose a reachable target location. In the confirmed variant, if the caller supplies a custom `location` during stage create and requests credential vending, Apache Polaris uses that location to construct delegated storage credentials immediately. The stage-create path itself neither runs the normal location validation nor the overlap checks before those credentials are issued. Closely related to that, the staged-create flow also accepts `write.data.path` / `write.metadata.path` in the request properties and feeds those location overrides into the same effective table location set used for credential vending. Those fields are secondary to the main custom-`location` exploit, but they are still attacker-influenced location inputs that should be validated before any credentials are issued.