SQL Injection Attacks

SQL Injection Attacks: An Overview

A SQL Injection attack is a method used by hackers to steal sensitive data from an organization's database. Hackers use vulnerabilities in application layer coding to introduce SQL commands into user input fields, allowing them to directly query the database and compromise its security. Understanding and preventing such threats are essential topics explained in an SQL Server tutorial or SQL Server Certification Course.

What is an SQL injection attack?

A SQL injection attack exploits a vulnerability in a web application, allowing hackers to change the queries being conducted on the underlying database. Web applications that immediately execute user inputs as queries are vulnerable to SQL injections. This enables attackers to run malicious queries, sometimes known as malicious payloads, on database servers.

SQL Injection: A Simple Example

To explain this issue, Let's create a table "tbluser" to describe the SQL Injection Attack.

Create table tbluser
(
 userName varchar(50) primary key,
 userpwd varchar(50),
 address varchar(100)
 )
insert into tbluser(userName,userpwd,address)values('mohan@gmail.com','123456','Delhi');
insert into tbluser(userName,userpwd,address)values('shailendra@gmail.com','123456','Noida');
insert into tbluser(userName,userpwd,address)values('jitendra@gmail.com','123456','Gurgaon');
insert into tbluser(userName,userpwd,address)values('bipul@gmail.com','123456','Delhi');
select * from tbluser 

Now let’s look at the following query string in Asp.net. In this we are passing username from TextBox "txtUserID" and userpwd from TextBox "txtpwd" to check user credentials.

"SELECT * FROM tbluser WHERE userName = '"+ txtUserID.text +"' and userpwd = '"+ txtPwd.text +"'"; 

Now hacker will pass the following input to TextBoxes to inject sql attack. What will happen when the below data goes as input?

"SELECT * FROM tbluser WHERE userName = ';Drop table tblusers --' and userpwd = '123'"; 

The semicolon; in the above statement will terminate the current sql. So, "SELECT * FROM tbluser WHERE UserID = ''" will become a separate statement, and after Semi Colon; it will start a new sql statement "Drop table tblusers" that will drop our table tbluser. Hence your user details table has been dropped and your database will be unmanaged.

Solution for SQL Injection Attack

1. In C# or VB.Net during building a SQL Statement, use the SqlParameter to define the Parameter Name, type, and value instead of making a straight command like above.

2. In Asp.Net query specify that CommandType as Text or Stored Procedure.

3. When we use Parameters Collection, we should use parameters the type and size will also be mentioned.

4. If we use stored procedure, instead of directly building by using Exec command, use sp_executesql command.

5. Another way to stop SQL injection attacks is to filter the user input for SQL characters. Use the REPLACE function to replace any apostrophe (single quotation mark to SQL) with an additional apostrophe. Within a SQL string, two consecutive single quotation marks are treated as an instance of the apostrophe character within the string.

Read More

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Summary

In this article, I try to explain the SQL Injection attack. I hope after reading this article will be aware of the SQL Injection attack. I would like to have feedback from my blog readers. Please post your feedback, questions, or comments about this article.

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