PHP Secure E-mails

There is a weakness in the PHP e-mail script in the previous chapter.

---

PHP E-mail Injections

First, look at the PHP code from the previous chapter:

if (isset($_REQUEST['email'])) //if "email" is filled out, send email { //send email $email = $_REQUEST['email'] ; $subject = $_REQUEST['subject'] ; $message = $_REQUEST['message'] ; mail("someone@example.com", "Subject: $subject", $message, "From: $email" ); echo "Thank you for using our mail form"; } else //if "email" is not filled out, display the form { echo " Email: Subject: Message: <br /> "; } ?>

The problem with the code above is that unauthorized users can insert data into the
mail headers via the input form.

What happens if the user adds the following text to the email input field in
the form?

someone@example.com%0ACc:person2@example.com %0ABcc:person3@example.com,person3@example.com, anotherperson4@example.com,person5@example.com %0ABTo:person6@example.com

The mail() function puts the text above into the mail headers as usual, and now the
header has an extra Cc:, Bcc:, and To: field. When the user clicks the submit
button, the e-mail will be sent to all of the addresses above!

---

PHP Stopping E-mail Injections

The best way to stop e-mail injections is to validate the input.

The code below is the same as in the previous chapter, but now we have added an input validator
that checks the email field in the form:

function spamcheck($field) { //filter_var() sanitizes the e-mail //address using FILTER_SANITIZE_EMAIL $field=filter_var($field, FILTER_SANITIZE_EMAIL); //filter_var() validates the e-mail //address using FILTER_VALIDATE_EMAIL if(filter_var($field, FILTER_VALIDATE_EMAIL)) { return TRUE; } else { return FALSE; } } if (isset($_REQUEST['email'])) {//if "email" is filled out, proceed //check if the email address is invalid $mailcheck = spamcheck($_REQUEST['email']); if ($mailcheck==FALSE) { echo "Invalid input"; } else {//send email $email = $_REQUEST['email'] ; $subject = $_REQUEST['subject'] ; $message = $_REQUEST['message'] ; mail("someone@example.com", "Subject: $subject", $message, "From: $email" ); echo "Thank you for using our mail form"; } } else {//if "email" is not filled out, display the form echo " Email: Subject: Message: <br /><br /> "; } ?>

In the code above we use PHP filters to validate input:

• The FILTER_SANITIZE_EMAIL filter removes all illegal e-mail characters
  from a string


• The FILTER_VALIDATE_EMAIL filter validates value as an e-mail address