XSS vulnerable app 000-f
Sep 25, 2019 Update: Aug 28, 2021
Since there are too many HTML tags to blacklist, we use a smart white list approach, in which we allow only b, i, and br.
HTML
CSS
JavaScript
<center>
<input type="text" id="input"/>
<div id="screen"></div>
</center>
document.querySelector('#input').addEventListener('keyup', function(e) {
if (e.keyCode === 13) {
let tagString = document.querySelector('#input').value;
// allow only `b`, `i`, and `br`
tagString = tagString.replace(/<(?!\s*b|i|br\s*\/?)[^>]+>/gi, '');
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#
- LOL
- Eg:
<Img/SrC/onerror=alert('LOL')> - Event listeners makes XSS possible for innocuous looking tags
- Eg:
<b onmouseover=alert(1)>click me!</b>