How can I avoid SQL injection attacks?

Question

Yesterday I was speaking with a developer, and he mentioned something about restricting the insertions on database field, like, strings such as -- (minus minus).

At the same type, what I know is that is a good approach to escape HTML chars like <, > etc. Not --. Is this true? Do I have to worry about --, ++? Is it more like a myth or old stuff?

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Update

Thanks a lot for all the answers, it's easy to understand like that since I'm kind of new to all of this. Well, to be more specific in this case our discussion was about and C# ASP.NET MVC website we're developing, so there's a complex open an account form in there with important information, so I'm not sure if MVC using Linq to interface with database already comes with this kind of protection or not. So if anyone could provides some hints about it, it would be great. Thanks again

Answer 1

The proper way to avoid SQL Injection attacks is NOT to simply disallow certain problematic characters, but rather to use parameterized SQL. In short, parameterized SQL prevents the database from executing raw user input as part of the SQL command this prevents user input like "drop table" from being executed. Just escaping characters does not stop all forms of SQL injection attacks and excluding certain words such as "Drop" does not work in all cases; there can be certain fields where "Drop" is a perfectly valid part of the data entry.

You can find some good articles on the subject of paramaterized SQL here:

https://blog.codinghorror.com/give-me-parameterized-sql-or-give-me-death/

http://www.codeproject.com/KB/database/ParameterizingAdHocSQL.aspx

Now that you mentioned that you are working with ASP.net I can give you some links that deal specifically with SQL Injection in ASP.

https://dzone.com/articles/aspnet-preventing-sql-injectio https://www.c-sharpcorner.com/UploadFile/75a48f/how-sql-injection-can-be-possible-in-asp-net-websites/

Here is a more general article on making your ASP more secure: http://www.codeproject.com/KB/web-security/Securing_ASP_NET_Apps.aspx

And, of course the MSDN article on SQL injection: http://msdn.microsoft.com/en-us/library/ms998271.aspx