• php
  • 1726
  • 20-3-2008
    • There is a weakness in the PHP e-mail script in the previous chapter. -------------------------------------------------------------------------------- [color=FA0309]PHP E-mail Injections[/color]
    First, look at the PHP code from the previous chapter:
    <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: $email" );
    echo "Thank you for using our mail form";
    }
    else
    //if "email" is not filled out, display the form
    {
    echo "<form method='post' action='mailform.php'>
    Email: <input name='email' type='text' /><br />
    Subject: <input name='subject' type='text' /><br />
    Message:<br />
    <textarea name='message' rows='15' cols='40'>
    </textarea><br />
    <input type='submit' />
    </form>";
    }
    ?>
    </body>
    </html>
    The problem with the code above is that unauthorized users can insert data into the mail headers via the input form. What happens if the user adds the following text to the email input field in the form?
    someone@example.com%0ACc:person2@example.com
    %0ABcc:person3@example.com,person3@example.com,
    anotherperson4@example.com,person5@example.com
    %0ABTo:person6@example.com
    The mail() function puts the text above into the mail headers as usual, and now the header has an extra Cc:, Bcc:, and To: field. When the user clicks the submit button, the e-mail will be sent to all of the addresses above! -------------------------------------------------------------------------------- [color=FA0309]PHP Stopping E-mail Injections[/color]
    The best way to stop e-mail injections is to validate the input. The code below is the same as in the previous chapter, but now we have added an input validator that checks the email field in the form:
    <html>
    <body>
    <?php
    function spamcheck($field)
    {
    //eregi() performs a case insensitive regular expression match
    if(eregi("to:",$field) || eregi("cc:",$field))
    {
    return TRUE;
    }
    else
    {
    return FALSE;
    }
    }//if "email" is filled out, send email
    if (isset($_REQUEST['email']))
    {
    //check if the email address is invalid
    $mailcheck = spamcheck($_REQUEST['email']);
    if ($mailcheck==TRUE)
    {
    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 "<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>
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