What potential pitfalls should be considered when processing user input in PHP, specifically when dealing with alphanumeric characters?

When processing user input in PHP, specifically when dealing with alphanumeric characters, potential pitfalls to consider include SQL injection attacks, cross-site scripting (XSS), and data validation errors. To mitigate these risks, always sanitize and validate user input before using it in any database queries or displaying it on a web page. 

// Sanitize and validate alphanumeric user input
$user_input = $_POST['user_input'];
$sanitized_input = filter_var($user_input, FILTER_SANITIZE_STRING);
$validated_input = preg_replace("/[^a-zA-Z0-9]/", "", $sanitized_input);

// Use $validated_input in your code

Keywords

SQL injection cross-site scripting htmlspecialchars filter_input validation

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