PHP secure emails

In the PHP e-mail script in the previous section, there is a vulnerability.

PHP E-mail Injection

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

<html>
<head>
<meta charset="utf-8">
<title>php中文网(php.cn)</title>
</head>
<body>
<?php
   if (isset($_REQUEST['email'])) { // 如果接收到邮箱参数则发送邮件
     // 发送邮件
     $email = $_REQUEST['email'] ;
     $subject = $_REQUEST['subject'] ;
     $message = $_REQUEST['message'] ;
      mail("someone@example.com", $subject,
     $message, "From:" . $email);
     echo "邮件发送成功";
   } else { // 如果没有邮箱参数则显示表单
     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 unauthorized users can insert data in the email header through the input form.

What will happen if the user adds the following text to the email in the input box 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

As usual, the mail() function puts the above text into Email header, then the header now has additional Cc:, Bcc: and To: fields. When the user clicks the submit button, this e-mail will be sent to all the addresses above!

PHP Prevent E-mail Injection

The best way to prevent e-mail injection is to validate the input.

The following code is similar to the one in the previous chapter, but here we have added an input validator to detect the email field in the form:

     <html>
        <head>
        <meta charset="utf-8">
        <title>php中文网(php.cn)</title>
        </head>
        <body>
        <?php
        function spamcheck($field)
        {
            // filter_var() 过滤 e-mail
            // 使用 FILTER_SANITIZE_EMAIL
            $field=filter_var($field, FILTER_SANITIZE_EMAIL);
            //filter_var() 过滤 e-mail
            // 使用 FILTER_VALIDATE_EMAIL
            if(filter_var($field, FILTER_VALIDATE_EMAIL))
            {
                return TRUE;
            }
            else
            {
                return FALSE;
            }
        }
        if (isset($_REQUEST['email']))
        {
            // 如果接收到邮箱参数则发送邮件
            // 判断邮箱是否合法
            $mailcheck = spamcheck($_REQUEST['email']);
            if ($mailcheck==FALSE)
            {
                echo "非法输入";
            }
            else
            {
                // 发送邮件
                $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
        {
            // 如果没有邮箱参数则显示表单
            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>

In the above code, we use PHP Filter to validate the input:

FILTER_SANITIZE_EMAIL Filter removes illegal characters of email from the string

FILTER_VALIDATE_EMAIL Filter validates the value of email address

You can Read more about filters in our PHP Filter.

Continuing Learning

new file

<html> <head> <meta charset="utf-8"> <title>php中文网(php.cn)</title> </head> <body> <?php function spamcheck($field) { // filter_var() 过滤 e-mail // 使用 FILTER_SANITIZE_EMAIL $field=filter_var($field, FILTER_SANITIZE_EMAIL); //filter_var() 过滤 e-mail // 使用 FILTER_VALIDATE_EMAIL if(filter_var($field, FILTER_VALIDATE_EMAIL)) { return TRUE; } else { return FALSE; } } if (isset($_REQUEST['email'])) { // 如果接收到邮箱参数则发送邮件 // 判断邮箱是否合法 $mailcheck = spamcheck($_REQUEST['email']); if ($mailcheck==FALSE) { echo "非法输入"; } else { // 发送邮件 $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 { // 如果没有邮箱参数则显示表单 echo "<form method='post' action='mailform.php'> Email: <input name='email' type='text'><br><br> Subject: <input name='subject' type='text'><br><br> Message:<br> <textarea name='message' rows='15' cols='40'> </textarea><br> <input type='submit'> </form>"; } ?> </body> </html>

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PHP secure emails

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