How can I avoid SQL injection attacks in my ASP.NET application?

Use parameters! It really is that simple :-)

Create your queries like this (for MS Sql server with C#):

SqlCommand getPersons = new SqlCommand("SELECT * FROM Table WHERE Name = @Name", conn); 

Here @Name is the parameter where you want to avoid sql injection and conn is an SqlConnection object. Then to add the parameter value you do the following:

getPersons.Parameters.AddWithValue("@Name", theName);

Here theName is a variable that contains the name you are searching for.

Now it should be impossible to do any sql injections on that query.

Since it is this simple there is no reason not to use parameters.

Use Prepared Statements (link to an ASP.NET tutorial that uses prepared statements in the 'To add nodes for products' section). that's all there is to it.

Well, that or use an ORM, like Linq to SQL or NHibernate, they internally use prepared statements.

Never trust user input - Validate all textbox entries using validation controls, regular expressions, code, and so on

Never use dynamic SQL - Use parameterized SQL or stored procedures

Never connect to a database using an admin-level account - Use a limited access account to connect to the database

Don't store secrets in plain text - Encrypt or hash passwords and other sensitive data; you should also encrypt connection strings

Exceptions should divulge minimal information - Don't reveal too much information in error messages; use customErrors to display minimal information in the event of unhandled error; set debug to false

Useful link on MSDN Stop SQL Injection

SQL injection occurs because the query to the database is being constructed in real time, for example:

SELECT * From Table1 WHERE " + UserInput

UserInput may be malicious and contain other statements that you do not intend.

To avoid it, you need to avoid concatenating your query together.

You can accomplish this by using parametrized queries - check out the DBCommand object for your particular DB flavor.

Use parametrized queries and/or stored procedures and parse your parameters via SQL parameters. Never generate SQL code by concatenating strings. Also do some reading about SQL injection and about writing secure code, because preventing SQL injection is only a small part of security. There is many more (like XSS - Cross Site Scripting). If a hacker wants to compromise your site/application he will look for more then only SQL injection.

Scott Guthrie posted a decent little article about this a while back. In it, he offers 5 suggestions for protecting yourself:

1. Don't construct dynamic SQL Statements without using a type-safe parameter encoding mechanism. [...]

2. Always conduct a security review of your application before ever put it in production, and establish a formal security process to review all code anytime you make updates. [...]

3. Never store sensitive data in clear-text within a database. [...]

4. Ensure you write automation unit tests that specifically verify your data access layer and application against SQL Injection attacks. [...]

5. Lock down your database to only grant the web application accessing it the minimal set of permissions that it needs to function. [...]

He does a decent job of explaining why these are important, and links to several other resources as well...

NEVER trust user input, always validate it, and use sql parameters. Should be enough basis to prevent SQL injection.

Hopefully, this will help:

http://www.codersbarn.com/post/2008/11/01/ASPNET-Data-Input-Validation.aspx

The short answer is to use parameterized queries.

Anthony :-) www.codersbarn.com

Always use only parameterized queries.

As others have said, don't concatenate user input to create dynamic sql statements; always use parameterized SQL when using dynamic SQL. However I will point out that this rule also applies when creating dynamic sql inside of a stored proc. This fact is something people often overlook. They think they are safe because they are "using stored procedures."

The book, "Building Secure ASP.NET Applications" guideline has a section on this topic.

Use XSS Secured UrlEncode using Microsoft.Security.Application.AntiXss.UrlEncode and SQL injection will not work. Or You can use ASP.NET – JSON – Serialization and Deserialization

Also test your application with SiteDigger from Macfee Fre Tool.

Few More are from here

.NET Security Toolkit v1.0 .NETMon v1.0 Validator.NET v1.0

Everyone says "Use parameters". We'd have to say it less if it wasn't so perversely difficult.

Use QueryFirst. The temptation to concatenate is removed, and the right way becomes the easiest way. You create a parameter just by typing @myParam in your SQL, the tool does the rest.

disclaimer: I wrote QueryFirst