Out of the box, Drupal has no ability to restrict viewing of site content, beyond a blanket “this role can/cannot access site content”. Unsurprisingly, then, the menu system does not ensure that users can actually view a node that a custom menu item refers to before placing it in the menu. If you’re using an add-on access control module like Taxonomy Access Control Lite or Category Access Control Lite (included in the Category package), this will have the undesirable effect of leaving menu items visible for content the user has no access to, creating a usability and minor security problem.
This module goes through the {menu} table, finds nodes which are inaccessible to the user, and adds them to the navigation menu with the access attribute set to FALSE, preventing them from appearing. I’ll hopefully be putting this up on http://drupal.org soon, but for now, you can get it here. Not available in stores! Download today!