Does the query builder prevent SQL Injection?

Does the query builder prevent SQL Injection? - c#

Hi all i'm currently working in ASP.NET using the query builder to create select, insert, update queries etc etc on some datasets which i have created in my App_Code folder. I have realised for you to use a parameters in the queries you have to use a "?" like so
SELECT * FROM users WHERE email = ?
what i was wondering is does this actually protect your tables from sql injection or do you need to do more in the code in order to protect the queries?

Parameterized queries accept parameters and input them as the appropriate SQL data type. So for example creating this proc
CREATE PROCEDURE GetStudent (IN LN VARCHAR(200))
BEGIN
SELECT Name FROM Students WHERE LastName = LN;
END
And passing this value (assume this is in your C# code.
"'Bobby'; DROP TABLE STUDENTS;"
Will essentially execute this query
SELECT Name FROM Students WHERE LastName ='''Bobby;''DROP TABLE Students'
Which is quite safe.
Of course, you will have to adapt for your particular application needs, but the general point is that parameterized queries are safe against SQL Injection for all major RDMSs.

Related

Updating a SQL table with double single-quotes [duplicate]

I am very new to working with databases. Now I can write SELECT, UPDATE, DELETE, and INSERT commands. But I have seen many forums where we prefer to write:
SELECT empSalary from employee where salary = #salary
...instead of:
SELECT empSalary from employee where salary = txtSalary.Text
Why do we always prefer to use parameters and how would I use them?
I wanted to know the use and benefits of the first method. I have even heard of SQL injection but I don't fully understand it. I don't even know if SQL injection is related to my question.

Using parameters helps prevent SQL Injection attacks when the database is used in conjunction with a program interface such as a desktop program or web site.
In your example, a user can directly run SQL code on your database by crafting statements in txtSalary.
For example, if they were to write 0 OR 1=1, the executed SQL would be
SELECT empSalary from employee where salary = 0 or 1=1
whereby all empSalaries would be returned.
Further, a user could perform far worse commands against your database, including deleting it If they wrote 0; Drop Table employee:
SELECT empSalary from employee where salary = 0; Drop Table employee
The table employee would then be deleted.
In your case, it looks like you're using .NET. Using parameters is as easy as:
string sql = "SELECT empSalary from employee where salary = #salary";
using (SqlConnection connection = new SqlConnection(/* connection info */))
using (SqlCommand command = new SqlCommand(sql, connection))
{
var salaryParam = new SqlParameter("salary", SqlDbType.Money);
salaryParam.Value = txtMoney.Text;
command.Parameters.Add(salaryParam);
var results = command.ExecuteReader();
}
Dim sql As String = "SELECT empSalary from employee where salary = #salary"
Using connection As New SqlConnection("connectionString")
Using command As New SqlCommand(sql, connection)
Dim salaryParam = New SqlParameter("salary", SqlDbType.Money)
salaryParam.Value = txtMoney.Text
command.Parameters.Add(salaryParam)
Dim results = command.ExecuteReader()
End Using
End Using
Edit 2016-4-25:
As per George Stocker's comment, I changed the sample code to not use AddWithValue. Also, it is generally recommended that you wrap IDisposables in using statements.

You are right, this is related to SQL injection, which is a vulnerability that allows a malicioius user to execute arbitrary statements against your database. This old time favorite XKCD comic illustrates the concept:
In your example, if you just use:
var query = "SELECT empSalary from employee where salary = " + txtSalary.Text;
// and proceed to execute this query
You are open to SQL injection. For example, say someone enters txtSalary:
1; UPDATE employee SET salary = 9999999 WHERE empID = 10; --
1; DROP TABLE employee; --
// etc.
When you execute this query, it will perform a SELECT and an UPDATE or DROP, or whatever they wanted. The -- at the end simply comments out the rest of your query, which would be useful in the attack if you were concatenating anything after txtSalary.Text.
The correct way is to use parameterized queries, eg (C#):
SqlCommand query = new SqlCommand("SELECT empSalary FROM employee
WHERE salary = #sal;");
query.Parameters.AddWithValue("#sal", txtSalary.Text);
With that, you can safely execute the query.
For reference on how to avoid SQL injection in several other languages, check bobby-tables.com, a website maintained by a SO user.

In addition to other answers need to add that parameters not only helps prevent sql injection but can improve performance of queries. Sql server caching parameterized query plans and reuse them on repeated queries execution. If you not parameterized your query then sql server would compile new plan on each query(with some exclusion) execution if text of query would differ.
More information about query plan caching

Two years after my first go, I'm recidivating...
Why do we prefer parameters? SQL injection is obviously a big reason, but could it be that we're secretly longing to get back to SQL as a language. SQL in string literals is already a weird cultural practice, but at least you can copy and paste your request into management studio. SQL dynamically constructed with host language conditionals and control structures, when SQL has conditionals and control structures, is just level 0 barbarism. You have to run your app in debug, or with a trace, to see what SQL it generates.
Don't stop with just parameters. Go all the way and use QueryFirst (disclaimer: which I wrote). Your SQL lives in a .sql file. You edit it in the fabulous TSQL editor window, with syntax validation and Intellisense for your tables and columns. You can assign test data in the special comments section and click "play" to run your query right there in the window. Creating a parameter is as easy as putting "#myParam" in your SQL. Then, each time you save, QueryFirst generates the C# wrapper for your query. Your parameters pop up, strongly typed, as arguments to the Execute() methods. Your results are returned in an IEnumerable or List of strongly typed POCOs, the types generated from the actual schema returned by your query. If your query doesn't run, your app won't compile. If your db schema changes and your query runs but some columns disappear, the compile error points to the line in your code that tries to access the missing data. And there are numerous other advantages. Why would you want to access data any other way?

In Sql when any word contain # sign it means it is variable and we use this variable to set value in it and use it on number area on the same sql script because it is only restricted on the single script while you can declare lot of variables of same type and name on many script. We use this variable in stored procedure lot because stored procedure are pre-compiled queries and we can pass values in these variable from script, desktop and websites for further information read Declare Local Variable, Sql Stored Procedure and sql injections.
Also read Protect from sql injection it will guide how you can protect your database.
Hope it help you to understand also any question comment me.

Old post but wanted to ensure newcomers are aware of Stored procedures.
My 10¢ worth here is that if you are able to write your SQL statement as a stored procedure, that in my view is the optimum approach. I ALWAYS use stored procs and never loop through records in my main code. For Example: SQL Table > SQL Stored Procedures > IIS/Dot.NET > Class.
When you use stored procedures, you can restrict the user to EXECUTE permission only, thus reducing security risks.
Your stored procedure is inherently paramerised, and you can specify input and output parameters.
The stored procedure (if it returns data via SELECT statement) can be accessed and read in the exact same way as you would a regular SELECT statement in your code.
It also runs faster as it is compiled on the SQL Server.
Did I also mention you can do multiple steps, e.g. update a table, check values on another DB server, and then once finally finished, return data to the client, all on the same server, and no interaction with the client. So this is MUCH faster than coding this logic in your code.

Other answers cover why parameters are important, but there is a downside! In .net, there are several methods for creating parameters (Add, AddWithValue), but they all require you to worry, needlessly, about the parameter name, and they all reduce the readability of the SQL in the code. Right when you're trying to meditate on the SQL, you need to hunt around above or below to see what value has been used in the parameter.
I humbly claim my little SqlBuilder class is the most elegant way to write parameterized queries. Your code will look like this...
C#
var bldr = new SqlBuilder( myCommand );
bldr.Append("SELECT * FROM CUSTOMERS WHERE ID = ").Value(myId);
//or
bldr.Append("SELECT * FROM CUSTOMERS WHERE NAME LIKE ").FuzzyValue(myName);
myCommand.CommandText = bldr.ToString();
Your code will be shorter and much more readable. You don't even need extra lines, and, when you're reading back, you don't need to hunt around for the value of parameters. The class you need is here...
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.SqlClient;
public class SqlBuilder
{
private StringBuilder _rq;
private SqlCommand _cmd;
private int _seq;
public SqlBuilder(SqlCommand cmd)
{
_rq = new StringBuilder();
_cmd = cmd;
_seq = 0;
}
public SqlBuilder Append(String str)
{
_rq.Append(str);
return this;
}
public SqlBuilder Value(Object value)
{
string paramName = "#SqlBuilderParam" + _seq++;
_rq.Append(paramName);
_cmd.Parameters.AddWithValue(paramName, value);
return this;
}
public SqlBuilder FuzzyValue(Object value)
{
string paramName = "#SqlBuilderParam" + _seq++;
_rq.Append("'%' + " + paramName + " + '%'");
_cmd.Parameters.AddWithValue(paramName, value);
return this;
}
public override string ToString()
{
return _rq.ToString();
}
}

Visual Studio 2019: run SQL query in C# with parameter coming from web form [duplicate]

I am very new to working with databases. Now I can write SELECT, UPDATE, DELETE, and INSERT commands. But I have seen many forums where we prefer to write:
SELECT empSalary from employee where salary = #salary
...instead of:
SELECT empSalary from employee where salary = txtSalary.Text
Why do we always prefer to use parameters and how would I use them?
I wanted to know the use and benefits of the first method. I have even heard of SQL injection but I don't fully understand it. I don't even know if SQL injection is related to my question.

Using parameters helps prevent SQL Injection attacks when the database is used in conjunction with a program interface such as a desktop program or web site.
In your example, a user can directly run SQL code on your database by crafting statements in txtSalary.
For example, if they were to write 0 OR 1=1, the executed SQL would be
SELECT empSalary from employee where salary = 0 or 1=1
whereby all empSalaries would be returned.
Further, a user could perform far worse commands against your database, including deleting it If they wrote 0; Drop Table employee:
SELECT empSalary from employee where salary = 0; Drop Table employee
The table employee would then be deleted.
In your case, it looks like you're using .NET. Using parameters is as easy as:
string sql = "SELECT empSalary from employee where salary = #salary";
using (SqlConnection connection = new SqlConnection(/* connection info */))
using (SqlCommand command = new SqlCommand(sql, connection))
{
var salaryParam = new SqlParameter("salary", SqlDbType.Money);
salaryParam.Value = txtMoney.Text;
command.Parameters.Add(salaryParam);
var results = command.ExecuteReader();
}
Dim sql As String = "SELECT empSalary from employee where salary = #salary"
Using connection As New SqlConnection("connectionString")
Using command As New SqlCommand(sql, connection)
Dim salaryParam = New SqlParameter("salary", SqlDbType.Money)
salaryParam.Value = txtMoney.Text
command.Parameters.Add(salaryParam)
Dim results = command.ExecuteReader()
End Using
End Using
Edit 2016-4-25:
As per George Stocker's comment, I changed the sample code to not use AddWithValue. Also, it is generally recommended that you wrap IDisposables in using statements.

You are right, this is related to SQL injection, which is a vulnerability that allows a malicioius user to execute arbitrary statements against your database. This old time favorite XKCD comic illustrates the concept:
In your example, if you just use:
var query = "SELECT empSalary from employee where salary = " + txtSalary.Text;
// and proceed to execute this query
You are open to SQL injection. For example, say someone enters txtSalary:
1; UPDATE employee SET salary = 9999999 WHERE empID = 10; --
1; DROP TABLE employee; --
// etc.
When you execute this query, it will perform a SELECT and an UPDATE or DROP, or whatever they wanted. The -- at the end simply comments out the rest of your query, which would be useful in the attack if you were concatenating anything after txtSalary.Text.
The correct way is to use parameterized queries, eg (C#):
SqlCommand query = new SqlCommand("SELECT empSalary FROM employee
WHERE salary = #sal;");
query.Parameters.AddWithValue("#sal", txtSalary.Text);
With that, you can safely execute the query.
For reference on how to avoid SQL injection in several other languages, check bobby-tables.com, a website maintained by a SO user.

In addition to other answers need to add that parameters not only helps prevent sql injection but can improve performance of queries. Sql server caching parameterized query plans and reuse them on repeated queries execution. If you not parameterized your query then sql server would compile new plan on each query(with some exclusion) execution if text of query would differ.
More information about query plan caching

In Sql when any word contain # sign it means it is variable and we use this variable to set value in it and use it on number area on the same sql script because it is only restricted on the single script while you can declare lot of variables of same type and name on many script. We use this variable in stored procedure lot because stored procedure are pre-compiled queries and we can pass values in these variable from script, desktop and websites for further information read Declare Local Variable, Sql Stored Procedure and sql injections.
Also read Protect from sql injection it will guide how you can protect your database.
Hope it help you to understand also any question comment me.

Old post but wanted to ensure newcomers are aware of Stored procedures.
My 10¢ worth here is that if you are able to write your SQL statement as a stored procedure, that in my view is the optimum approach. I ALWAYS use stored procs and never loop through records in my main code. For Example: SQL Table > SQL Stored Procedures > IIS/Dot.NET > Class.
When you use stored procedures, you can restrict the user to EXECUTE permission only, thus reducing security risks.
Your stored procedure is inherently paramerised, and you can specify input and output parameters.
The stored procedure (if it returns data via SELECT statement) can be accessed and read in the exact same way as you would a regular SELECT statement in your code.
It also runs faster as it is compiled on the SQL Server.
Did I also mention you can do multiple steps, e.g. update a table, check values on another DB server, and then once finally finished, return data to the client, all on the same server, and no interaction with the client. So this is MUCH faster than coding this logic in your code.

Other answers cover why parameters are important, but there is a downside! In .net, there are several methods for creating parameters (Add, AddWithValue), but they all require you to worry, needlessly, about the parameter name, and they all reduce the readability of the SQL in the code. Right when you're trying to meditate on the SQL, you need to hunt around above or below to see what value has been used in the parameter.
I humbly claim my little SqlBuilder class is the most elegant way to write parameterized queries. Your code will look like this...
C#
var bldr = new SqlBuilder( myCommand );
bldr.Append("SELECT * FROM CUSTOMERS WHERE ID = ").Value(myId);
//or
bldr.Append("SELECT * FROM CUSTOMERS WHERE NAME LIKE ").FuzzyValue(myName);
myCommand.CommandText = bldr.ToString();
Your code will be shorter and much more readable. You don't even need extra lines, and, when you're reading back, you don't need to hunt around for the value of parameters. The class you need is here...
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.SqlClient;
public class SqlBuilder
{
private StringBuilder _rq;
private SqlCommand _cmd;
private int _seq;
public SqlBuilder(SqlCommand cmd)
{
_rq = new StringBuilder();
_cmd = cmd;
_seq = 0;
}
public SqlBuilder Append(String str)
{
_rq.Append(str);
return this;
}
public SqlBuilder Value(Object value)
{
string paramName = "#SqlBuilderParam" + _seq++;
_rq.Append(paramName);
_cmd.Parameters.AddWithValue(paramName, value);
return this;
}
public SqlBuilder FuzzyValue(Object value)
{
string paramName = "#SqlBuilderParam" + _seq++;
_rq.Append("'%' + " + paramName + " + '%'");
_cmd.Parameters.AddWithValue(paramName, value);
return this;
}
public override string ToString()
{
return _rq.ToString();
}
}

Dynamic build query & SQL Injection & DLLs files

I have read a lot of things about SQL injection and many arguments why you should avoid to build your query dynamically using plain code/concatenations within your cs.file
However, I have question and I need some advice from someone with more experience than me.
I created some DLL files in order to re-use my code in different projects and for that reason I was thinking generic.
I created these DLL files that contained all the logic/code of building SQL queries in a dynamic way + concatenation of statement. Thereafter, I add these DLL files as reference to my project.
This will be vulnerable to SQL Injection ? also is that insufficient procedure (time consuming/insufficient maintenance)?
Any advice would be appreciated.

If you are not processing your input that you are passing to your query (built at run time) you are vulnerable to SQL injection. Adding to dll or not doesn't makes any difference.
To overcome this you need to use parameterised queries. They have multiple advantages a part from security.
One reason that i can think of right now is that you have a text box. And your query is
"select * from table1 where name = '" + textbox1.Text;
Not lets assume that in textbox1 user enters Ehsan's. Your query will go bang and won't even execute.
Example of parameterised query
"select * from table1 where name = #Name"
yourCommand.Parameters.AddWithValue("#Name", textbox1.Text);

It's difficult to know for sure but if you do something like
string sql = "SELECT Field FROM Table WHERE Field = " + Somevar;
Then you are open to SQL injection if somevar comes from input of some kind (usually user input).
There is just no reason to do it as you can just do
string sql = "SELECT Field FROM Table WHERE Field = #myvar"

You should make sure you are using parameterized queries or stored procedures, etc.
And avoid using dynamic SQL queries such as
"SELECT * FROM Users WHERE UserID = " + UserID
as these are vulnerable to SQL Injection
Instead use a parameterized query or a stored procedure, e.g.
"SELECT * FROM Users WHERE UserID = #UserID"
Most ORMs (eg .NET's Entity Framework) will provide some protection against SQL Injection (but only if used properly)
this link explains in more detail http://www.troyhunt.com/2013/07/everything-you-wanted-to-know-about-sql.html

What's the best practice in executing a stored procedure with multiple parameters using MVC3?

I am working at implementing a search feature into my MVC3 application. I'm looking to pass two parameters into and execute a stored procedure that will look basically something like this:
create procedure MyProc
(
#FirstParam nvarchar(50),
#SecondParam nvarchar(20)
)
as select * from MyTable where #FirstParam like #SecondParam
MyTable has about 30 fields that will be returned for each object and I need to create a procedure like this for several tables, so I am trying to avoid using a SqlDataReader and converting the returned Sql data to C#.
I would like to use something like this method but I am not sure if this can be done with multiple parameters.
Ideally I would like to use EF4, but I have not found any good information on executing stored procedures while using EF4.
Any insight on the most painless way and/or best practice for executing this task will be greatly appreciated.

My sugestion is use dynamic linq (and here, and here). You can pass valid linq expressions as regular strings:
var column = "Name";
var value = "Marvin";
var query = DbCtx.MyEntity.Where("{0} == #1", columnName, value);
The benefits (IMO) is that you can keep the search logic in the application and, if you need to do this for many tables, you can create a T4 template to generate the bootstrap code for you.

What you are suggesting can indeed be done through parameters, and you should be using an ORM like EF4 for you data access. Like most ORM that have support for stored procedure, you can indeed pass multiple parameters to the stored procedure.
The issue you will find, however, is that you can't have dynamic column names in SQL Server (or any other SQL database that I am aware of) - you can't give a column name in a variable.
You will need to use dynamic SQL to achieve this, either within the stored procedure or otherwise.

SQL injection on INSERT

I have created a small survey web page on our company Intranet. This web page is not accessible from the outside.
The form is simply a couple of radio buttons and a comments box.
I would like to maintain good coding practices and would like to guard against SQL Injections.
Can SQL injections happen on a insert statement with comments from the textbox?
If so, how can I guard against it using .NET 2.0?

Injection can happen on any SQL statement not run properly.
For example, let's pretend your comment table has two fields, an integer ID and the comment string. So you'd INSERT as follows:
INSERT INTO COMMENTS VALUES(122,'I like this website');
Consider someone entering the following comment:
'); DELETE FROM users; --
If you just put the comment string into the SQL without any processesing this could turn your single INSERT in to the following two statements followed by a comment:
INSERT INTO COMMENTS VALUES(123,''); DELETE FROM users; -- ');
This would delete everything from your users table. And there are people willing to spend all day finding the right tablename to empty using trial and error and various tricks. Here's a description of how you could perform an SQL Injection attack.
You need to use parameterized SQL statements to prevent this.
And this isn't just for security reasons. For example, if you're creating your SQL statements naively the following comment:
I'm just loving this website
would cause an SQL syntax error because of the apostrophe being interpreted by SQL as a closing quote.

Use parameterized queries so that the text is automatically quoted for you.
SqlCommand command = connection.CreateCommand();
command.CommandText = "insert into dbo.Table (val1,val2,txt) values (#val1,#val2,#txt)";
command.AddParameterWithValue( "val1", value1 );
command.AddParameterWithValue( "val2", value2 );
command.AddParameterWithValue( "txt", text );
...

SQL injection can happen any time you pass a query back to the database. Here's a simple demonstration:
SQL Injection Explained
The key, within .NET, is to do as Dave Webb has given. It will prevent the injection attempt by encompassing the entire string as one parameter to be submitted, handling all characters that might be interpreted by SQL Server to change the query or append additional commands.
And it should be pointed out that SQL injection can occur on any application, not just web applications. And that an internal attack is usually the most costly to an organization. One cannot safely assume that an attack won't originate from within.

In addition to using prepared statements and parameters rather than concatenating strings into your SQL you should also do the following:
Validate and format user input on the server side. Client side validation and limits can easily be bypasses with tools like WebScarab, or by spoofing your form.
Configure appropriate permissions for the database user account. Web application should use a separate account or role in your database with permissions restricted to only the tables, views and procedures required to run your application. Make sure that user does not have select rights on the system tables
Hide detailed error messages from users, and use less common names for your objects. It amazes me how often you can determine the server type (oracle, mysql, sqlserver) and find basic schema information in an error message and then get information from tables called 'user(s)', 'employee(s)'. If you haven't set your permissions as in (2) and I can determine your server type you are open to statements like this for SQL Server
SELECT table_name FROM information_schema.table
EXECUTE sp_help foundTableName

Yes, they can happen. The easiest way to guard against this is to use prepared statements rather than building the SQL manually.
So, rather than this:
String sql =
String.Format("INSERT INTO mytable (text_column) VALUES ( '{0}' )",
myTextBox.Text); // Unsafe!
You would do something like this:
String sql = "INSERT INTO mytable (text_column) VALUES ( ? )"; // Much safer
Then add the text of the text box as a parameter to your DbCommand which will cause it to be automatically escaped and replace the "?" in the SQL.

Prevent SQL Injection by using prepared statement. The use of placehoder(?) totally eliminates sql Injection Vulnerability.
example
String sql=Select * from user_table where username='+request.getparameter("username")+';
statement.executeQuery(sql);
the above statement is vulnerable to sql injection.
To make it safe against sql injection.
Use following the snippet
String sql=Select * from user_table where username=?;
statement.setString(1,username);

Yes, it can. Let's say the client sends this:
OR 1 = 1
That can be very painfull for your
SELECT * FROM admin WHERE name = #name AND password = #password
You can prevent this with
using Parameter class from ADO.NET
using regexp
reading, reading: http://www.codeproject.com/KB/database/SqlInjectionAttacks.aspx

The easiest way to guard against that form of SQL injection, is to use parameters and stored procedures rather then building sql statements to run. (In C# or internally to SQL Server).
However I'm not entirely sure you should be spending time on this, unless of course it's your corporate policy, as the chances of it ever occuring internally are minimal at best, and if it did occur, I would hope you would know immediately who it is.

Develop Reference

C# (C-Sharp) is a programming language developed by Microsoft that runs on the .NET Framework.