Here is a clear, safe, and practical guide to SQL Injection, including what it is, how it works, and how to prevent it in real-world systems.

⚠️ What Is SQL Injection?

SQL Injection (SQLi) is a critical security vulnerability that allows attackers to inject malicious SQL code into a query, often leading to:

• Unauthorized data access

• Data modification or deletion

• Authentication bypass

• Complete database takeover

SQL Injection occurs when user input is incorrectly handled and gets executed as SQL.

❌ Example of Vulnerable (Insecure) Code

If an attacker enters:

The resulting query becomes:

✔ Always TRUE → attacker logs in without a password.

🎯 Types of SQL Injection

1. Classic (In-band) SQL Injection

Directly manipulates SQL queries.

2. Blind SQL Injection

Database errors/results are hidden, so attackers infer information slowly.

3. Boolean-based Blind SQLi

Returns different pages based on TRUE/FALSE.

4. Time-based Blind SQLi

Uses delays (SLEEP(5)) to infer TRUE/FALSE.

5. Out-of-band SQL Injection

Uses external channels (DNS, HTTP callbacks).

🛡 How to Prevent SQL Injection (Best Practices)

1️⃣ Use Prepared Statements (Parameterized Queries)

This is the #1 recommended defense.

Example (MySQL, PostgreSQL, SQL Server)

Example (PHP PDO)

✔ User input is treated as data, not executable code.

2️⃣ Use Stored Procedures Safely

(Still requires parameterization—stored procedures alone don’t guarantee safety.)

3️⃣ Validate and Sanitize Input

• Accept only expected characters (e.g., alphanumeric)

• Reject unexpected characters (', ", ;, --, etc.)

• Enforce strong data types

4️⃣ Apply the Principle of Least Privilege

Use database accounts with minimal rights:

• No DROP permissions

• No ALTER permissions

• No access to unnecessary tables

5️⃣ Disable Detailed Error Messages

Error messages can reveal:

• Table names

• Column names

• SQL syntax

• Database version

Use generic error messages in production.

6️⃣ Use ORM Frameworks (Safely)

Frameworks like:

• Hibernate

• Entity Framework

• Sequelize

• Django ORM

These automatically parameterize queries—but avoid raw SQL without placeholders.

7️⃣ Web Application Firewall (WAF)

A WAF can block common SQL Injection payloads before they reach the application.

🔥 Real-World Attack Examples (Educational Only)

Authentication Bypass

Dump all data from a table

Blind timing attack

⚠️ Never try these on systems you don’t own—illegal and unethical.
Use them only in security labs or test environments.

📌 How to Test for SQL Injection (Safely)

Use tools like:

• Burp Suite

• sqlmap (in authorized pentests only)

• OWASP ZAP

And refer to OWASP SQL Injection Prevention Cheat Sheet.

🧠 Summary of Best Practices (Quick Checklist)

✔ Always use prepared statements
✔ Validate and sanitize input
✔ Avoid dynamic SQL and string concatenation
✔ Limit database permissions
✔ Hide SQL errors in production
✔ Use modern frameworks and ORMs
✔ Implement logging + monitoring
✔ Use WAF or intrusion detection systems