Using SQL Server Stored Procedures To Prevent SQL Injection
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by Randy Dyess
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Basic SQL Injection Attack
To demonstrate the advantages of using a stored procedure over embedded SQL, try a basic SQL Injection attack against our logon screen.

user name: foo' OR 1=1--
with no password

This simple SQL Injection attack will give you access to the site, even though we did not supply a valid user name and password.

Now use this small attack against our logon.asp page utilizing the stored procedure to access the database. You will have to modify the logon.asp page to call processlogon_sp.asp instead of processlogon.asp.

user name: foo' OR 1=1--
with no password

As you can tell from the results return by the logon.asp page, parameterized stored procedures can go a long way in protecting your database applications from SQL Injection. Given no input validation, the parameterized stored procedure still does not allow you to gain access to the site. As stated above, I would not drop all validation from your inputs; just add parameterized stored procedures as a second layer of protection.

Granted the example attack was not very complex but it is enough to show you how dangerous embedded SQL statements can be and how simple it is to create a stored procedure to validate users with your standard logon screen.

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User Comments

Title: terer'   
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Title: Mr   
Name: David MD
Date: 2009-11-24 3:35:03 AM
So where exactly do I write these stored procedures? in the SQL or
Title: God   
Name: Joe
Date: 2008-05-14 3:09:15 PM
' or 1=1 --
Title: Mr.   
Name: CSC
Date: 2007-05-17 3:21:16 PM
Good article, should then cover some basic validation. For those still wanting to use passed in SQL lest we forget that stored procs in SQL are pre compiled and the passed in string does not have to be parsed by the Query Analyzer which then has to build an execution plan. For a stored proc the execution plan is already compiled and in cache. Also a great follow up may be using OUTPUT parameters whenever returning only one row of data and how this can be up to 10x or more faster than using a recordset object for a single row.
Title: Mr.   
Name: Nikhil
Date: 2007-03-27 9:03:38 PM
really good. made very easy and comprehensive.
Title: SQL Injection works without stored procedures too   
Name: Adi
Date: 2006-07-18 3:45:02 PM
good basic aricle
Title: stored procedure   
Name: prakash
Date: 2006-05-21 12:54:48 AM
please its not sufficient.u must go through details from the begining.
Title: Setting Paramters for Stored Procedures   
Name: Dirty Sanchez
Date: 2004-09-15 2:50:17 PM
In the line:
SET objParam = objConn.CreateParameter("@strLogin",200, 1, 50)
What are the 200, 1, 50 doing?


Title: SQL Injection works without stored procedures too   
Name: Sid
Date: 2004-06-15 10:38:35 AM
It may be worthwhile to note that you do not have to use a stored procedure in order to use parameters. Here's an example:

Set cmd = Server.CreateObject("ADODB.Command")
Set rs = Server.CreateObject("ADODB.Recordset")
sql = "SELECT pkUserId FROM Users WHERE email = @email AND password = @password"

cmd.CommandText = sql
Set param = cmd.CreateParameter("@email", adVarChar, adParamInput, 255, Request.Form("txtEmail"))
cmd.Parameters.Append param
Set param = cmd.CreateParameter("@password", adVarChar, adParamInput, 255, Request.Form("txtPassword"))
cmd.Parameters.Append param
cmd.ActiveConnection = con

Set rs = cmd.Execute

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