SQL Injection Prevention: The Ultimate Developer Guide

What is SQL Injection?

SQL injection (SQLi) is a code injection technique that exploits vulnerabilities in applications that use SQL databases. Attackers can insert malicious SQL statements into input fields, potentially gaining unauthorized access to data, modifying records, or even executing administrative operations.

Vulnerable Code Example

Here's an example of vulnerable code that concatenates user input directly into a SQL query:

// ❌ VULNERABLE CODE - Never do this!
const query = "SELECT * FROM users WHERE username = '" + username + "'";

// Attacker input: ' OR '1'='1
// Resulting query: SELECT * FROM users WHERE username = '' OR '1'='1'
// This returns ALL users in the database!

Prevention Techniques

1. Parameterized Queries (Prepared Statements)

The most effective defense against SQL injection is using parameterized queries:

// ✅ SECURE CODE - Using parameterized queries
// Node.js with MySQL
const query = "SELECT * FROM users WHERE username = ?";
connection.execute(query, [username], callback);

// Python with psycopg2
cursor.execute("SELECT * FROM users WHERE username = %s", (username,))

// Java with PreparedStatement
PreparedStatement stmt = conn.prepareStatement(
    "SELECT * FROM users WHERE username = ?"
);
stmt.setString(1, username);

2. Input Validation

Validate and sanitize all user inputs:

• Use allowlists for expected input patterns
• Validate data types, lengths, and formats
• Reject inputs containing SQL keywords when unexpected

3. Use ORM Frameworks

Object-Relational Mapping frameworks provide built-in protection:

// ✅ Using Prisma ORM (Node.js)
const user = await prisma.user.findFirst({
  where: { username: username }
});

// ✅ Using Django ORM (Python)
user = User.objects.filter(username=username).first()

Testing for SQL Injection

Regular security testing is essential to identify SQL injection vulnerabilities before attackers do. SecuraProbe automatically tests for various SQL injection attack vectors including:

• Classic SQL injection
• Blind SQL injection (Boolean-based and Time-based)
• Union-based SQL injection
• Error-based SQL injection