php - How to output HTML but prevent XSS attacks

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php - How to output HTML but prevent XSS attacks

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

I wrote a php script to fetch the email content.

These contents are HTML format.

I'd like to display the content, as below

<?php 
$email_content = '
    <html>
        <script>alert("XSS");</script>
        <body>
            <div>Line1</div>
            <div>Line2</div>
        </body>
    </html>
';
echo $email_content;
?>

As you can see, it will cause XSS attacks. But if I use htmlspecialchars function, it will not show the correct HTML format, how should I do in this case? Thanks.

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1 Answer

深蓝 · Answer 1 · 2021-10-17T03:08:56+0000

HTMLPurifer can do that:

require_once '/path/to/HTMLPurifier.auto.php';

$config = HTMLPurifier_Config::createDefault();
$purifier = new HTMLPurifier($config);
$clean_html = $purifier->purify($dirty_html);

It takes dirty HTML (ie possibly containing Javascript) and removes any script.

PHP doesn't have anything native or built in that can remove Javacript like HTMLPurifier. You could use DOMDocument but this would be a lengthy task because Javascript can execute in some attributes (onerror, onclick) and is not just limited to <script></script>.

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