What are the potential security risks associated with allowing users to input PHP scripts in their signatures, and how can these risks be mitigated?

Allowing users to input PHP scripts in their signatures can pose a significant security risk as it opens up the possibility of malicious code execution on the server. To mitigate this risk, it is essential to sanitize and validate user input to ensure that only safe and permitted scripts are allowed. 

// Sanitize and validate user input before allowing it in signatures
$signature = $_POST['signature'];
$allowed_tags = '<b><i><u>'; // Define a list of allowed HTML tags

$filtered_signature = strip_tags($signature, $allowed_tags); // Strip any tags not in the allowed list

echo $filtered_signature; // Output the sanitized signature

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