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Simple Rules to Prevent SQL Injections


Previously I written around 7 computer security related articles (mostly on web security and cyber security), and this is my first article or post on RDBMS data or database application security.

In this article I will explain in short what are sql injections and simple rules to prevent sql injections, I want to say thanks to my friend Vaibhav Shringi (DB expert and IITian) for his help to prepare this post.

What is SQL injection?

SQL injection is a type of security exploit in which the attacker adds SQL code to a Web form input box or any other manner to gain access to resources or make changes to data.

How to Prevent SQL Injection Attacks? 

Simple Rules to Prevent SQL Injections

1. Sanitize the Input:

It's absolutely vital to sanitize user inputs to insure that they do not contain dangerous codes, whether to the SQL server or to HTML itself.

We should always attempt to allow only required characters approach not to stuff “Bad characters”

There is really no benefit in allowing characters that could not be valid, and rejecting them early - presumably with an error message - not only helps forestall SQL Injection, but also catches mere typos early rather than stores them into the database.

Better prevention: White List Input Validation

2. Escape/Quotesafe the input:

We can’t sanitize the inputs which allows special characters eg. “Bill O'Reilly” is a valid name.

Always use QUOTENAME() function in SQL statements if user input are required in In-line queries.

3. Use Bound Parameters:

Though quote-safing is a good mechanism, we're still in the area of "considering user input as SQL", and a much better approach exists: bound parameters, which are supported by essentially all database programming interfaces.


            PreparedStatement ps = connection.prepareStatement(
             "SELECT email FROM member WHERE name = ?");
            ps.setString(1, formField);
            ResultSet rs = ps.executeQuery();


This is probably the single most important step one can take to secure a web application.


4. Limit database permissions and segregate users:

The web application ought to use a database connection with the most limited rights possible: query-only access to the members table, and no access to any other table. If required can move to higher rights after successful login. 

It prevents unauthorized updates/delete/drop operations.
We should not use “SA” or same level rights’ users.

 5. Use stored procedures for database access:

Use stored procedures for performing access on the application's behalf, which can eliminate SQL entirely. By encapsulating the rules for a certain action - query, update, delete, etc. - into a single procedure, it can be tested and documented on a standalone basis and business rules enforced.



      Create PROCEDURE [dbo].[ReadUserDetails]
                -- Add the parameters for the stored procedure here
          @userName varchar(50)
           SELECT * FROM [UserDetails] where userName= @userName


C# code that’s use SP:

  public static DataTable ExecuteSelectCommand(string StoredProcedureName)
            // SqlCommand cmd = null;
            var table = new DataTable();
                using (var con = new SqlConnection(GetConnectionString()))
                    using (var cmd = new SqlCommand(StoredProcedureName, con))
                        cmd.CommandType = CommandType.StoredProcedure;
                        //cmd.CommandText = commandName;
                        SqlDataAdapter da = null;
                        using (da = new SqlDataAdapter(cmd))
            return table;

6. Isolate the webserver:

Even having taken all these mitigation steps, it's nevertheless still possible to miss something and leave the server open to compromise.

Isolated webserver with limited network pinholes can assure limited access to other servers in case of full webserver control.


7. Configure error reporting:

The default error reporting for some frameworks includes developer debugging information, and this cannot be shown to outside users. Imagine how much easier a time it makes for an attacker if the full query is shown, pointing to the syntax error involved.

This information is useful to developers, but it should be restricted - if possible - to just internal users.

धन्यवाद मित्रो !! 

Thanks Friends 

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