Computer SQL Injection

 

What is Computer SQL Injection? A Complete Guide

In today’s interconnected digital world, websites and online applications rely heavily on databases to store and manage information. These databases often use SQL (Structured Query Language) to retrieve, update, or delete data. However, if a web application does not handle SQL queries securely, it becomes vulnerable to a dangerous type of cyber attack called SQL Injection. This article explains what SQL Injection is, how it works, its types, risks, real-world examples, and how to protect against it.

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Understanding SQL and Databases

Before diving into SQL Injection, it’s important to understand what SQL is. SQL stands for Structured Query Language and is used to interact with relational databases. A database is like a digital filing cabinet where websites store data such as usernames, passwords, posts, messages, and more.

Common SQL operations include:

• SELECT – Retrieve data from a database

• INSERT – Add new data

• UPDATE – Modify existing data

• DELETE – Remove data

These operations are often triggered by user input on websites, like login forms or search bars.

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What is SQL Injection?

SQL Injection (SQLi) is a type of cyber attack that allows hackers to interfere with the queries that an application makes to its database. In simple terms, the attacker enters malicious SQL code into a web form or URL, tricking the system into executing unintended commands.

This can result in unauthorised access to data, data manipulation, or even complete control over the server. SQL Injection is one of the oldest and most dangerous web vulnerabilities.

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How SQL Injection Works

Let’s use an example to illustrate:

Suppose you have a login form on a website that asks for a username and password. The application might run a SQL query like this:

sql

SELECT * FROM users WHERE username = 'john' AND password = '12345';

If the input is not properly filtered, an attacker could enter the following as the username:

bash

' OR '1'='1

And leave the password blank. The resulting SQL query would become:

sql

SELECT * FROM users WHERE username = '' OR '1'='1' AND password = '';

Since '1'='1' is always true, the database will return a valid user, allowing the attacker to bypass authentication.

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Types of SQL Injection

SQL Injection comes in several forms depending on how the attacker delivers and manipulates the SQL code:

1. Classic (In-Band) SQL Injection

This is the most straightforward type. The attacker sees immediate results of the attack on the same page.

• Error-based SQLi: The attacker intentionally triggers database errors to learn about its structure.

• Union-based SQLi: Combines multiple SELECT statements to extract data from other tables.

2. Blind SQL Injection

Here, the application does not display error messages or return visible results. Instead, the attacker sends multiple queries and observes how the website behaves.

• Boolean-based: The attacker sends queries that return true or false results to gather information.

• Time-based: The attacker sends commands that make the database wait, allowing them to infer responses based on delay times.

3. Out-of-Band SQL Injection

This rare type sends data to a different server or method, such as email or DNS requests. It’s used when direct feedback isn’t possible or when other methods are blocked.

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Risks and Impacts of SQL Injection

SQL Injection can lead to severe consequences, such as:

• Data Theft: Hackers can access personal information, including usernames, passwords, credit card numbers, and more.

• Data Loss or Deletion: Attackers can delete entire databases or modify data.

• Unauthorised Access: SQLi can be used to bypass login systems and gain admin privileges.

• System Takeover: In extreme cases, it allows hackers to run system-level commands and take full control of the server.

• Legal Consequences: Organisations may face lawsuits, fines, and reputation damage due to data breaches caused by SQLi.

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Real-World Examples of SQL Injection

Several high-profile attacks have been caused by SQL Injection, including:

• Heartland Payment Systems (2008): Attackers used SQLi to steal over 100 million credit card numbers.

• Sony Pictures (2011): Hackers exploited SQL Injection to leak personal information of over 1 million users.

• British Airways (2018): Although more complex, the attack began with a vulnerability similar to SQLi and led to a major data breach.

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How to Prevent SQL Injection

Preventing SQL Injection is crucial for website and application security. Here are key strategies:

1. Use Prepared Statements (Parameterised Queries)

These queries separate SQL code from user input, preventing it from being treated as executable code.

python

cursor.execute("SELECT * FROM users WHERE username = ? AND password = ?", (username, password))

2. Input Validation and Sanitation

Always check and clean user input before using it in a query. Reject suspicious characters or patterns.

3. Use Stored Procedures

Stored procedures are SQL functions stored in the database. They provide more control and can reduce risk when used properly.

4. Limit Database Permissions

Give the application only the permissions it needs—nothing more. Avoid using admin-level access in regular queries.

5. Error Handling

Avoid displaying database errors to users. These messages can give hackers clues about the database structure.

6. Use Web Application Firewalls (WAFs)

A WAF can detect and block SQL Injection attempts before they reach the application.

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Conclusion

SQL Injection is a dangerous and widespread cyber threat that targets the heart of web applications—their databases. By exploiting weak input validation and insecure coding practices, hackers can steal data, cause damage, or take over systems. Understanding how SQL Injection works and implementing proper defences is essential for developers, businesses, and users alike. As cyber attacks continue to evolve, staying informed and vigilant is the first step toward a secure digital future.