PostgreSQL Server -- execute arbitrary SQL code as DBA user

The PostgreSQL project reports:

    Confine additional operations within "security restricted
    operation" sandboxes.
  

    Autovacuum, CLUSTER, CREATE INDEX, REINDEX, REFRESH MATERIALIZED VIEW,
    and pg_amcheck activated the "security restricted operation" protection
    mechanism too late, or even not at all in some code paths.
    A user having permission to create non-temporary objects within a
    database could define an object that would execute arbitrary SQL
    code with superuser permissions the next time that autovacuum
    processed the object, or that some superuser ran one of the affected
    commands against it.