What are the Best PHP Functions for Sanitizing and Escaping User Input?

What are the best PHP input sanitizing functions?

Problem:

You need to ensure that user input is safe for storage and display. However, there are numerous PHP filtering functions available, leaving you uncertain about which ones to employ.

Answer:

It's crucial to distinguish between sanitizing and validating user data, escaping data for storage, and escaping data for presentation.

Sanitizing and Validating User Data:

• Sanitize and Filter: Use filter types or casting to ensure expected data types. For free-form text, consider htmlspecialchars for escaping HTML or strip_tags or HTML Purifier for removing HTML.
• Validate: Verify that submitted data conforms to expected values and constraints using PHP filter validation functions, type checking, or specialized libraries like is_email for email addresses.

Escaping Data for Storage:

• Use prepared statements with data binding to protect against SQL injection. PHP PDO and database-specific extensions like mysqli provide safe data handling.
• Ensure data is stored in appropriate formats based on database specifications.

Escaping Data for Presentation:

• Escape user-generated data with htmlspecialchars before outputting it in HTML.
• For Javascript, use json_encode to provide sanitized values.

Additional Considerations:

• Character Set Encoding: Ensure UTF-8 encoding throughout your application to avoid encoding-related vulnerabilities.
• Cookie Security: Treat cookies as untrusted user input and validate them accordingly.
• Web Application Security: Data validation and escaping are integral to web application security, and understanding attack methodologies is essential for building effective defenses.

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