SQL injection is a security vulnerability that occurs when untrusted user input is directly included in a SQL query without proper validation or sanitization. It allows an attacker to manipulate the structure of the query and potentially execute unintended SQL commands. SQL injection attacks can lead to unauthorized access, data leakage, data manipulation, or even full control of the database.

Here are some key points about SQL injection:

1. Attack Scenario: SQL injection attacks typically occur when user input is concatenated directly into a SQL query string. This input can come from web forms, user inputs, or any other data source that is used to construct SQL queries.

2. Exploitation: An attacker can exploit a SQL injection vulnerability by providing specially crafted input that alters the intended behavior of the SQL query. By manipulating the input, attackers can modify the query's logic, extract sensitive data, bypass authentication mechanisms, or even execute arbitrary SQL commands.

3. Examples of Attacks: SQL injection attacks can take different forms, such as:

- Retrieving unauthorized data: Attackers can modify the query to retrieve data they are not supposed to have access to.
- Modifying or deleting data: Attackers can inject additional SQL statements to modify or delete data in the database.
- Authentication bypass: Attackers can craft input to bypass login mechanisms and gain unauthorized access.
- Command execution: Attackers can inject SQL commands that are executed by the database server, potentially allowing them to execute arbitrary code or commands.

4. Prevention Techniques: Preventing SQL injection involves using secure coding practices:

- Parameterized Queries/Prepared Statements: Instead of concatenating user input directly into the SQL query, use parameterized queries or prepared statements that separate the SQL logic from the user input. These mechanisms bind the input values to the query separately, preventing the injection of malicious code.
- Input Validation/Sanitization: Validate and sanitize user input to ensure it adheres to the expected format, type, and length. This can include input validation at the client-side (e.g., JavaScript validation) and server-side input validation and sanitization routines.
- Principle of Least Privilege: Ensure that database accounts used by the application have minimal privileges required for their intended functionality. Avoid using accounts with extensive administrative privileges that could potentially cause more harm if compromised.
- Security Auditing: Regularly review and audit the application's codebase and database configuration to identify and fix potential vulnerabilities. Perform penetration testing and code reviews to identify and mitigate SQL injection risks.
- WAF and Security Tools: Utilize web application firewalls (WAFs) and security tools that can help detect and block SQL injection attempts. These tools often include signature-based detection and protection against common SQL injection patterns.

SQL injection is a serious security concern that can have severe consequences if not properly addressed. It is important for developers and database administrators to follow secure coding practices, validate and sanitize user input, and regularly update and patch software to mitigate the risk of SQL injection vulnerabilities.