In the context of PHP, what are some common mistakes to avoid when handling data extracted from links in a web application?

One common mistake to avoid when handling data extracted from links in a web application is not properly sanitizing and validating the data before using it. This can lead to security vulnerabilities such as SQL injection or cross-site scripting attacks. To solve this issue, always sanitize and validate any data extracted from links before processing or displaying it.

// Sanitize and validate data extracted from a link
$linkParam = $_GET['param'];

// Sanitize the parameter using filter_var
$sanitizedParam = filter_var($linkParam, FILTER_SANITIZE_STRING);

// Validate the parameter to ensure it meets certain criteria
if (strlen($sanitizedParam) > 0) {
    // Proceed with using the sanitized and validated parameter
    echo "Parameter: " . $sanitizedParam;
} else {
    // Handle invalid parameter
    echo "Invalid parameter";
}