<a title="Oracle Database Listener Security Guide Oracle Database Listener Security Guide < Eddie Awad’s Blog
There's a link to a good solid Oracle Listener security guide over at Eddie Awad's blog.
The link to the doc. itself is here .
The doc. does a good job of covering off what is a reasonably poorly understood area of Oracle security, well worth a read if it's an area you're involved in, or at least worth forwarding to your DBA's as I'd be willing to bet that many of them aren't aware of how insecure the listener is by default...