What are common pitfalls when passing hidden fields in PHP forms?

Common pitfalls when passing hidden fields in PHP forms include not validating the data received from the hidden fields, not properly sanitizing the input to prevent SQL injection or other attacks, and not using encryption or hashing to secure sensitive information. To solve these issues, always validate and sanitize the data received from hidden fields, and consider encrypting or hashing sensitive information before passing it through hidden fields.

// Validate and sanitize the data received from hidden fields
$hidden_field_data = isset($_POST['hidden_field']) ? $_POST['hidden_field'] : '';
$clean_hidden_field_data = filter_var($hidden_field_data, FILTER_SANITIZE_STRING);

// Encrypt or hash sensitive information before passing it through hidden fields
$encrypted_data = openssl_encrypt($clean_hidden_field_data, 'AES-256-CBC', 'secret_key', 0, 'secret_iv');