The NewNotebook API does not sufficiently sanitize its parameters allowing an authenticated user with NOTEBOOK_EDIT permission to write the notebook record outside the org's data store directory. The file written must have an extension of ".json.db" but can otherwise overwrite other metadata files (such as ACL records, hunts etc). This can corrupt these files and cause data corruption.
The attacker must have at least the "analyst" role to be able to create new notebooks.