Question

I have a project (private, ASP.net website, password protected with https) where one of the requirements is that the user be able to enter Sql queries that will directly query the database. I need to be able to allow these queries, while preventing them from doing damage to the database itself, and from accessing or updating data that they shouldn’t be able to access/update.

I have come up with the following rules for implementation:

1. Use a db user that only has permission for Select Table/View and Update Table (thus any other commands like drop/alter/truncate/insert/delete will just not run).
2. Verify that the statement begins with the words ‘Select’ or ‘Update’
3. Verify (using Regex) that there are no instances of semi-colons in the statement that are not surrounded by single-quotes, white space and letters. (The thought here is that the only way that they could include a second query would be to end the first with a semi-colon that is not part of an input string).
4. Verify (using Regex) that the user has permission to access the tables being queried/updated, included in joins, etc. This includes any subqueries. (Part of the way that this will be accomplished is that the user will be using a set of table names that do not actually exist in the database, part of the query parsing will be to substitute in the correct corresponding table names into the query).

Am I missing anything?

The goal is that the users be able to query/update tables to which they have access in any way that they see fit, and to prevent any accidental or malicious attempts to damage the db. (And since a requirement is that the user generate the sql, I have no way to parametrize the query or sanitize it using any built-in tools that I know of).

Answer 1

Well, you already have enough people telling you ‘dont’ do this’, so if they aren’t able to dissuade you, here are some ideas:

INCLUDE the Good, Don’t try to EXCLUDE the bad
(I think the proper terminology is Whitelisting vs Blacklisting ) By that, I mean don’t look for evil or invalid stuff to toss out (there are too many ways it could be written or disguised), instead look for valid stuff to include and toss out everything else.

You already mentioned in another comment that you are looking for a list of user-friendly table names, and substituting the actual schema table names. This is what I’m talking about–if you are going to do this, then do it with field names, too.

I’m still leaning toward a graphical UI of some sort, though: select tables to view here, select fields you want to see here, use some drop-downs to build a where clause, etc. A pain, but still probably easier.