A bug in "BaseSerialization.deserialize()" allowed unrestricted "import_string()" of attacker-controlled class paths when the Scheduler / API Server loaded a serialized DAG: a DAG author could embed a malicious trigger into a DAG to gain remote code execution on the API Server / Scheduler process, crossing the Airflow security boundary that DAG-author code must never execute in those processes. Users are advised to upgrade to "apache-airflow" 3.3.0 or later. As a defense-in-depth mitigation, deployments where DAG-author trust is limited can restrict the "[core] allowed_deserialization_classes" config to a narrow allowlist.