What is the main issue with the PHP code provided for the header redirection from a variable?

The main issue with the PHP code provided for the header redirection from a variable is that the variable containing the URL is not properly sanitized, which can lead to security vulnerabilities like header injection attacks. To solve this issue, you should sanitize the variable before using it in the header function to prevent any malicious input.

// Sanitize the URL variable before using it in header redirection
$redirect_url = filter_var($redirect_url, FILTER_SANITIZE_URL);

// Perform the header redirection using the sanitized URL
header("Location: " . $redirect_url);
exit();