Glossary/SQL Injection (SQLi)
Web Security

SQL Injection (SQLi)

A code injection technique that exploits security vulnerabilities in database queries.

SQL Injection (SQLi) is one of the most common and dangerous web application vulnerabilities. It occurs when an attacker can insert or "inject" malicious SQL code into queries that an application sends to its database.

How SQL Injection Works

When a web application uses user-supplied input in SQL queries without proper sanitization, an attacker can manipulate the query to:

  • Extract sensitive data from the database (usernames, passwords, credit card numbers)
  • Modify or delete data in the database
  • Bypass authentication mechanisms
  • Execute administrative operations on the database
  • Types of SQL Injection

    TypeDescriptionDetection Difficulty
    In-band SQLiResults returned directly in the responseEasy
    Blind SQLiNo visible error messages, inferred from behaviorMedium
    Out-of-band SQLiData exfiltrated through separate channelHard

    Example

    A vulnerable login form might construct a query like:

    SELECT * FROM users WHERE username = '$input' AND password = '$password'

    An attacker could input: ' OR '1'='1' -- to bypass authentication.

    Prevention

  • Use parameterized queries (prepared statements)
  • Implement input validation and sanitization
  • Apply the principle of least privilege to database accounts
  • Use Web Application Firewalls (WAFs)
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