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Zend Framework 2 Documentation (Manual) |  |
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File: /_sources/modules/zend.escaper.escaping-javascript.txt
| Size: | 3501 |
| Storage flags: | no_autoload,compress/gzip (37%) |
.. _zend.escaper.escaping-javascript:
Escaping Javascript
===================
Javascript string literals in HTML are subject to significant restrictions particularly due to the potential for
unquoted attributes and any uncertainty as to whether Javascript will be viewed as being CDATA or PCDATA by the
browser. To eliminate any possible XSS vulnerabilities, Javascript escaping for HTML extends the escaping rules of
both ECMAScript and JSON to include any potentially dangerous character. Very similar to HTML attribute value escaping,
this means escaping everything except basic alphanumeric characters and the comma, period and underscore characters
as hexadecimal or unicode escapes.
Javascript escaping applies to all literal strings and digits. It is not possible to safely escape other Javascript
markup.
To escape data in the **Javascript context**, use ``Zend\Escaper\Escaper``'s ``escapeJs`` method. An extended set
of characters are escaped beyond ECMAScript's rules for Javascript literal string escaping in order to prevent
misinterpretation of Javascript as HTML leading to the injection of special characters and entities.
.. _zend.escaper.escaping-javascript.bad-examples:
Examples of Bad Javascript Escaping
-----------------------------------
An example of incorrect Javascript escaping:
.. code-block:: php
:linenos:
<?php header('Content-Type: application/xhtml+xml; charset=UTF-8'); ?>
<!DOCTYPE html>
<?php
$input = <<<INPUT
bar"; alert("Meow!"); var xss="true
INPUT;
$output = json_encode($input);
?>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Unescaped Entities</title>
<meta charset="UTF-8"/>
<script type="text/javascript">
<?php
// this will result in
// var foo = "bar"; alert("Meow!"); var xss="true";
?>
var foo = <?php echo $output ?>;
</script>
</head>
<body>
<p>json_encode() is not good for escaping javascript!</p>
</body>
</html>
The above example will show an alert popup box as soon as the page is loaded, because the data is not properly
escaped for the Javascript context.
.. _zend.escaper.escaping-javascript.good-examples:
Examples of Good Javascript Escaping
------------------------------------
By using the ``escapeJs`` method in the Javascript context, such attacks can be prevented:
.. code-block:: php
:linenos:
<?php header('Content-Type: text/html; charset=UTF-8'); ?>
<!DOCTYPE html>
<?php
$input = <<<INPUT
bar"; alert("Meow!"); var xss="true
INPUT;
$escaper = new Zend\Escaper\Escaper('utf-8');
$output = $escaper->escapeJs($input);
?>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Escaped Entities</title>
<meta charset="UTF-8"/>
<script type="text/javascript">
<?php
// this will look like
// var foo = bar\x26quot\x3B\x3B\x20alert\x28\x26quot\x3BMeow\x21\x26quot\x3B\x29\x3B\x20var\x20xss\x3D\x26quot\x3Btrue;
?>
var foo = <?php echo $output ?>;
</script>
</head>
<body>
<p>Zend\Escaper\Escaper::escapeJs() is good for escaping javascript!</p>
</body>
</html>
In the above example, the Javascript parser will most likely report a ``SyntaxError``, but at least the targeted
application remains safe from such attacks.
For more information about the PHK package format: http://phk.tekwire.net