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

Question

I need to avoid being vulnerable to SQL injection in my ASP.NET application. How might I accomplish this?

Answer 1

Try to use Stored Procedures, and validate the input on your data. Do not use any direct SQL like INSERT INTO ...

Answer 2

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.

Answer 3

Even though your question is very generic, a few rules always apply:

• Use parameterized queries (SqlCommand with SqlParameter) and put user input into parameters.
• Don't build SQL strings out of unchecked user input.
• Don't assume you can build a sanitizing routine that can check user input for every kind of malformedness. Edge cases are easily forgotten. Checking numeric input may be simple enough to get you on the safe side, but for string input just use parameters.
• Check for second-level vulnerabilites - don't build SQL query strings out of SQL table values if these values consist of user input.
• Use stored procedures to encapsulate database operations.

Answer 4

SQL injection occurs because the query to the database is being constructed in real time, EG "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.

Answer 5

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.

Answer 6

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

Answer 7

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...

Answer 8

Always use only parameterized queries.

Answer 9

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

Answer 10

Understand what exactly SQL Injection is and then never write anything that is vulnerable to it.

Answer 11

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

Answer 12

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.

Answer 13

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

Answer 14

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."