How to sanitize the query?

Question

I have this SQL Query which I want to sanitize:

SELECT * FROM navigation_$cat ORDER BY parent ASC, prio ASC

The problem is that I can't get the $cat sooner because it's being send via AJAX, and indicates which database needs to be accessed. How can I create a PDO statement that is safer than simply putting a string together?

Answer 1

You can implement a whitelist, but another option would be to check for valid input using:

SHOW TABLES LIKE :tblname

and 'navigation_'.$cat as the parameter. Check that this returns exactly one table, and that the returned table exactly matches the passed parameter.

Once that's done, you know it's safe to inject into the query, because you've ascertained that it is indeed a valid table name.

That being said, "dynamically selecting from an unknown-in-advance table" is usually a sign that you're designing your database wrong, and you should probably just have one navigation table with a category column inside.