CVE-2026-58076: Apache Airflow: Unguarded import_string() of airflow_exc_ser / base_exc_ser exception nodes in BaseSerialization.deserialize enables DAG-author RCE on Scheduler / API Server

Apache Airflow's serialization layer reconstructed exception nodes by calling importstring() on a class name taken from the serialized blob and instantiating it with arguments from the same blob, with no restriction on what could be imported. An operator's executorconfig reaches that branch, so a Dag author could place a value there that causes an arbitrary callable to be imported and invoked -- for example subprocess.checkoutput, or builtins.eval on the builtins-prefixed variant. The code runs in the Scheduler, which reconstructs serialized Dags in its normal loop with no request involved, and in the API server, on any authenticated read of the Dag such as GET /api/v2/dags/{dagid}/details. Both are components the Airflow security model states must never execute Dag-author code, and both hold the metadata database credentials and the JWT signing secret. No non-default configuration is required. This is a different sink from CVE-2026-33264, which covered only the trigger branch of the same deserializer: deployments that upgraded in response to that advisory are still affected through the exception branch and must upgrade again. Users are advised to upgrade to apache-airflow 3.3.1 or later, which restricts the imported class to a subclass of BaseException.