SQL INJECTION

What is SQL Injection?

SQL Injection is a security vulnerability where untrusted input alters an SQL query’s intent, allowing unauthorized data access or manipulation.

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Compatible dialects for SQL INJECTION: All major databases (PostgreSQL, MySQL, SQL Server, Oracle, SQLite, MariaDB, Snowflake, etc.) are susceptible when queries are built unsafely.

SQL INJECTION Full Explanation

SQL Injection (SQLi) occurs when an application concatenates unvalidated, user-supplied data into an SQL statement. Because the database parses the entire string as executable code, an attacker can inject additional clauses (e.g., `OR 1=1`, `UNION SELECT`, or stacked queries) to read, modify, or destroy data, bypass authentication, and escalate privileges. Vulnerable code typically builds queries via string interpolation, relies on manual escaping, or exposes error messages that reveal schema details. Defenses center on using parameterized queries or prepared statements (which send SQL and data separately to the server), strict input validation, least-privilege accounts, stored procedures that avoid dynamic SQL, and centralized error handling. Major compliance regimes (PCI-DSS, HIPAA, GDPR) require controls against SQLi. Pen-testers exploit it with tools like sqlmap. Modern ORM libraries default to prepared statements, but developers must avoid raw, interpolated SQL. Blind SQLi, time-based SQLi, and out-of-band SQLi work even when error messages are hidden. Always audit logs and rotate credentials after an incident.

SQL INJECTION Syntax

-- Vulnerable
SELECT * FROM users WHERE username = '" + user + "' AND password = '" + pass + "';

-- Safe (parameterized)
SELECT * FROM users WHERE username = ? AND password = ?;

SQL INJECTION Parameters

Example Queries Using SQL INJECTION

-- Classic attack: Bypass login
username: admin' --
password: anything

Resulting SQL:
SELECT * FROM users WHERE username = 'admin' -- ' AND password = 'anything';

-- Data exfiltration via UNION
id_param = 1 UNION SELECT name, credit_card, exp_date FROM payments;

Expected Output Using SQL INJECTION

In the first example, the attacker logs in as admin without the correct password
In the second, the query returns payment data alongside normal results, leaking sensitive information

Use Cases with SQL INJECTION

Security testing by red teams and auditors
Hardening applications with prepared statements
Teaching developers secure coding practices
Incident response to data breaches involving SQLi

Common Mistakes with SQL INJECTION

Believing ORM frameworks eliminate all SQLi
Relying solely on client-side validation
Escaping input manually instead of binding parameters
Granting application accounts DBA-level privileges

First Introduced In

Recognized as a vulnerability in late 1990s web applications

Frequently Asked Questions

What is the difference between SQL Injection and Cross Site Scripting?

SQL Injection targets the database by manipulating SQL commands, while Cross Site Scripting (XSS) injects malicious scripts into web pages to run in visitors’ browsers.

Can stored procedures stop SQL Injection?

Stored procedures that avoid dynamic SQL help, but procedures that build queries with concatenation remain vulnerable. Always use parameters.

How can I test my application for SQL Injection?

Use automated scanners like sqlmap, add single-quote fuzzing (`'" or 1=1 --`), and review code for string-built SQL. Run tests in a staging environment only.

Is prepared statement performance impacted?

Prepared statements may add minimal overhead on first execution, but caching and plan reuse typically make them as fast or faster than ad-hoc SQL.