First, look at the PHP code in the previous section:
<html> <body> <? php 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 "<form method = 'post' action = 'mailform.php'> Email: <input name = 'email' type = 'text' /> <br /> Subject: <input name = 'subject' type = 'text' /> <br /> Message: <br /> <textarea name = 'message' rows = '15' cols = '40 '> </ textarea> <br /> <input type =' submit '/> </ form> ";}?> </ Body> </ html>The problem with the above code is that an unauthorized user can insert data into the header of a message by entering the form.
If the user in the form of the input box to join these text, what will happen?
someone@example.com%0ACc: person2@example.com% 0ABcc: person3 @ example.com, person3@example.com, anotherperson4@example.com, person5 @ example.com% 0ABTo: person6@example.comAs usual, the mail () function puts the above text in the header of the message, so now the header has additional Cc :, Bcc:, and To: fields. When the user clicks the submit button, this e-mail will be sent to all the above address!
PHP to prevent E-mail injectionThe best way to prevent e-mail injection is to validate the input.
The code below is similar to the previous section, but we have added the input validation procedure for email fields in the test form:
<html> <body> <? php 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 $ $ subject = $ _REQUEST ['subject']; $ message = $ _REQUEST ['message']; mail ("someone@example.com", "Subject: $ subject", $ echo "Thank you for using our mail form";}} else {// if "email" is not filled out, display the form echo "<form method = 'post' action = 'mailform.php'> Email: <input name = 'email' type = 'text' /> <br /> Subject: <input name = 'subject' type = 'text' /> <br /> Message: <br /> <text area name = 'message' rows = '15 'cols = '40'> </ textarea> <br /> <input type = 'submit' /> </ form> ";}?> </ body> </ html >In the code above, we used a PHP filter to validate the input:
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