XSS vulnerable app 002-b
Sep 25, 2019 Update: Aug 28, 2021
Strip HTML from all user-submitted inputs using military grade regex, whether you print them on screen on not.
HTML
CSS
JavaScript
<center>
Enter your username:
<p>
<input type="text" id="input"/>
<div id="screen"></div>
</p>
</center>
document.querySelector('#input').addEventListener('keyup', function(e) {
if (e.keyCode === 13) {
const username = document.querySelector('#input').value.replace(/(<([^>]+)>)/, '');
const tagString = `<div data-user=${username}>😉 Not today, ${username}!</div>`;
const range = document.createRange();
range.selectNode(document.getElementsByClassName('applet').item(0));
const documentFragment = range.createContextualFragment(tagString);
document.querySelector('#screen').appendChild(documentFragment);
}
});
#input {
font-size: 16px;
height: 26px;
width: 100%;
margin-bottom: 10px;
padding: 20px;
}
.applet-html {
padding: 20px;
}
.applet {
margin-bottom: 20px;
}Takeaways and notes#
- You don't need to print any user-submitted data to the screen to cause XSS
- If you are writing a user-submitted input to the DOM, you could be vulnerable to XSS
- Eg:
"<x>onmouseover=alert(1)>