How Can I Securely Handle User Input in PHP to Prevent Attacks?

PHP User Input Sanitization: A Paradigm Shift

Sanitizing user input is crucial to protect against SQL injection and XSS attacks. However, the common notion of filtering input is flawed. Instead, focus on properly formatting data for the context it will be used in.

Prepared Statements for SQL Queries

Instead of concatenating variables into SQL strings, use prepared statements with parameters. This ensures that data is formatted correctly, protecting against SQL injection.

htmlspecialchars for HTML Output

When embedding strings in HTML markup, use htmlspecialchars to escape special characters, preventing XSS attacks. This should be applied to all echo and print statements.

Escaping for Shell Commands

If using external commands with exec, use escapeshellcmd and escapeshellarg to escape strings and arguments, protecting against command injection.

json_encode for JSON

Avoid manual JSON string creation and use json_encode instead. JSON formatting is complex, and a dedicated function ensures proper formatting.

Preformatted Input as an Exception

The only exception to the above approach is sanitizing preformatted input, such as user-submitted HTML. This should be avoided whenever possible due to security concerns.

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