Lil’ Bobby Tables

A while back I found xkcd. I found it through a mailing list but this post grabbed my attention. Here’s a recent comic which made me think about the way that popular web applications use SQL databases. If you don’t get it the
Mom in the comic executed a classic SQL injection attack against her son’s school. (BTW I didn’t want to spoil the joke. You can see the previous sentence by highlighting it with your mouse.) In any case this is a common attack method against many current web applications and it shows just how naively many of the programmers are of SQL in general. There are two practical ways to defend against this attack. The most obvious is to validate your SQL before you pass it to the database engine. One that requires a little more thought would be to disallow the web database user from being able to DROP TABLES in the first place. Any real web application should expect a database with at least two users, root, or dba and webuser, or www. Root should be allowed to do anything to the database but his credentials need to be protected. If your web application has grown to the point where you’ve split your database server from your webserver for performance purposes. Allowing the root or dba level of access from localhost only is a good start. Webuser should be able to SELECT on your applications tables. He should be able to INSERT, UPDATE, and DELETE on a limited subset of tables as your database will allow. He may need to be able to CREATE a temporary table and possible DROP the same but that’s a job that’s really better done by a stored procedure. E.g. create a stored procedure that does the needed manipulation and then allow the webuser the privilege to call the stored. Obviously what you can do here depends on your database. I know that Postgresql can grant these very fine grained security settings. If I recall correctly MySQL is a little more course but is still workable.