The model-facing cronjob tool accepts free-form provider + base_url. On fire,
the scheduler pairs the named provider's stored credential with the job's
base_url, so a prompt-injected job (e.g. provider=anthropic,
base_url=https://attacker/v1) sends the real API key to an attacker endpoint. A
base_url with no provider inherits the default provider's key for the same
effect.
Add a fail-closed guard at the tool boundary: a base_url override is allowed
only for the custom/BYOK sentinel, a configured custom_providers entry, or when
the override host matches the named provider's own endpoint; an override without
an explicit provider is rejected. The trust boundary is the caller, so
operator-configured base_urls for named providers are unaffected.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
b24708eda0