The PHP mail() function, which allows sending emails from within a PHP application, has several parameters that can be used to inject malicious commands. The 5th parameter, $additional_parameters, allows an attacker to append program flags to the mail program, potentially leading to remote command execution and server compromise. This vulnerability was recently discovered in popular applications such as Roundcube, PHPMailer, Zend Framework, SwiftMailer, and SquirrelMail, which also affected widely used applications like WordPress, Joomla, and Drupal due to their integration with these libraries. To use the mail() function securely, developers must carefully analyze the arguments of each call and ensure that user input is not used directly in the 5th parameter, as even escaping or quoting routines can be broken. A restrictive email filter can also be applied to limit input to a minimal set of characters, but this breaks RFC compliance. An alternative approach has been developed by Paul Buonopane.