SQL Injection Attacks

SQL Injection Attacks

24 Mar 2024
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4 min read

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.

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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.

FAQs

Q1. How can SQL Injection attacks happen in SQL Server?

SQL Injection attacks make use of vulnerabilities in SQL Server applications, allowing attackers to avoid input validation and insert malicious SQL queries to interact with the database.

Q2. How can SQL injection attacks be avoided in SQL Server applications?

To limit database access, use parameterized queries, input validation, stored procedures, and enforce the least privilege principle.

Q3. What are some common indicators of a SQL Injection attack in SQL Server logs?

SQL Injection attacks can be detected by looking for strange patterns in SQL Server log files, such as many failed login attempts, unexpected database activity, and unusual queries.

Q4. Can SQL Injection attacks be automated on SQL Server databases?

Yes, attackers use automated techniques to scan and exploit SQL Injection vulnerabilities in SQL Server applications, which highlights the importance of patching and securing systems frequently.

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About Author
Shailendra Chauhan (Microsoft MVP, Founder & CEO at Scholarhat by DotNetTricks)

Shailendra Chauhan is the Founder and CEO at ScholarHat by DotNetTricks which is a brand when it comes to e-Learning. He provides training and consultation over an array of technologies like Cloud, .NET, Angular, React, Node, Microservices, Containers and Mobile Apps development. He has been awarded Microsoft MVP 8th time in a row (2016-2023). He has changed many lives with his writings and unique training programs. He has a number of most sought-after books to his name which has helped job aspirants in cracking tough interviews with ease.
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