Introduction to SQL Injection

Introduction to SQL Injection

• SQL injection is a code injection technique used to attack data-driven applications.
• It lets attackers manipulate the database queries executed by the application.
• This can lead to unauthorized access, data breaches, and other security vulnerabilities.

How SQL Injection Works

• Attackers inject malicious SQL code into input fields.
• The application, without proper validation, treats the injected code as legitimate SQL commands.
• The injected code modifies the database's intended queries and yields unintended results.
• For example, attackers can use SQL statements like ' OR '1'='1 to bypass authentication or DELETE FROM users; to delete all users from a database.

Types of SQL Injection

• In-band SQL injection: Attackers retrieve the results of their injected SQL statements directly in the application's response.
• Inferential SQL injection: An indirect attack where attackers infer database schema and data by analyzing the application's responses to different SQL queries.
• Out-of-band SQL injection: Exploits alternate channels (e.g., mail server or remote file system) to communicate with the database—less common due to detection.

Vulnerable Code Examples

• Code that directly concatenates user input to SQL queries without sanitization.
• Code that lacks parameterized queries.
• Code with improperly validated user-supplied input.

Prevention Techniques

• Input Validation: Validate and sanitize all user-supplied input before using in SQL queries.
• Parameterized Queries: Use parameterized queries (prepared statements), ensuring user input is treated as data, not code, separating data from the query structure.
• Stored Procedures: Use stored procedures to encapsulate database operations, usually with better validation.
• Least Privilege Principle: Give database accounts only the necessary privileges.
• Output Encoding: Encode special characters in output to prevent further manipulation.
• Web Application Firewalls (WAFs): Detect and block malicious SQL injection attacks.
• Regular Updates: Keep databases and web applications updated with the latest security patches.

Preventing SQL Injection in Parameterized Queries

• Parameterized queries treat user input as data, not part of the SQL command, preventing malicious input from affecting query execution.
• Modern programming languages often have built-in support for parameterized queries or prepared statements.

Impact of SQL Injection Attacks

• Unauthorized access to sensitive data.
• Data modification or deletion.
• Denial-of-service attacks on the database.
• System compromise via database access.
• Financial loss due to data breaches.
• Reputational damage to organizations.

Common SQL Injection Attack Vectors

• Input fields (usernames, passwords, search boxes, forms).
• Cookies and HTTP headers.
• Hidden form fields.
• Using query parameters without proper quoting.

Detection Techniques

• Penetration testing.
• Security tools (like WAFs) for malicious pattern monitoring.
• Observing error messages in web application responses.
• Reviewing security logs regularly.

Mitigation Strategies

• Secure coding practices.
• Implementing input validation rules.
• Consistent use of parameterized queries.
• Using stored procedures, when appropriate.
• Strengthening database access controls.