What potential security risks should be considered when allowing users to input HTML code into a textarea and saving it as a file?

Allowing users to input HTML code into a textarea and saving it as a file can pose security risks such as cross-site scripting (XSS) attacks. To mitigate this risk, it is important to sanitize and validate the user input before saving it as a file. This can be done by stripping out any potentially harmful HTML tags or attributes.

// Sanitize and validate user input before saving it as a file
$user_input = $_POST['user_input'];

// Remove potentially harmful HTML tags and attributes
$sanitized_input = strip_tags($user_input);

// Save the sanitized input as a file
$file = fopen("user_input.html", "w");
fwrite($file, $sanitized_input);
fclose($file);