01 What is SQL Injection?
SQL Injection (SQLi) is a code injection technique where an attacker executes malicious SQL statements that control a web application's database server.
By exploiting this vulnerability, an attacker can bypass authentication, access, modify, or delete data within the database, and in some cases, even issue administrative commands to the database operating system.
The Query
An application builds a database query using user input (e.g., login form).
The Trick
Attacker enters ' OR '1'='1 which alters the logic of the query.
The Breach
The database treats the input as code, granting the attacker access.
02 How It Works
Imagine a login query:
SELECT * FROM users WHERE username = '$user' AND password = '$pass';If an attacker enters admin' -- as the username, the query becomes:
SELECT * FROM users WHERE username = 'admin' --' AND password = '...';The -- acts as a comment in SQL, ignoring the rest of the line (the password check). The attacker is logged in as 'admin' without a password.
03 Impact of SQLi
The consequences of a successful SQL injection attack are severe:
Unauthorized Access
Attackers can bypass logins and gain administrative access to your application, controlling everything from user data to site settings.
Data Theft
SQLi is a primary vector for data breaches. Attackers can dump entire tables containing passwords, emails, credit card details, and personal information.
Data Loss
Attacks aren't always about stealing. An attacker could execute DROP TABLE users, effectively destroying your business's data instantly.
Reputation Damage
A data breach destroys customer trust. Recovering from a public disclosure of leaked user data is incredibly difficult and costly.
04 Prevention Strategies
Fortunately, SQL injection is completely preventable with the right coding practices.
1. Prepared Statements (Parameterized Queries)
This is the gold standard. Instead of concatenating strings, you use placeholders (e.g., `?` or `$1`). The database treats the user input as data, never as executable code.
2. Use Stored Procedures
Stored procedures encapsulate the SQL query on the database server. Like prepared statements, they generally prevent SQL injection by treating parameters as data.
3. Principle of Least Privilege
Your web application should connect to the database with limited permissions. It should not run as `root` or `sa`, preventing attackers from dropping tables or accessing system files.
05 Frequently Asked Questions
Do ORMs like Prisma or TypeORM prevent SQL injection?
Yes, most modern ORMs use parameterized queries by default, which effectively prevents SQL injection. However, using 'raw' queries without parameters can still leave you vulnerable.
Is SQL injection only a problem for PHP sites?
No. SQL injection affects any application that communicates with a database using SQL, regardless of the language (Node.js, Python, Java, etc.).
Can a firewall stop SQL injection?
A Web Application Firewall (WAF) can detect and block common SQL injection patterns, but it is a mitigation layer, not a fix for the underlying code vulnerability.
What is Blind SQL Injection?
Blind SQLi occurs when an application is vulnerable but doesn't return database errors. Attackers infer data by asking true/false questions to the database.
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