DOM XSS in AngularJS expression with angle brackets and double quotes HTML-encoded

Description

The website in this lab contains a DOM-based cross-site scripting vulnerability in a AngularJS expression within the search functionality.

AngularJS is a popular JavaScript library, which scans the contents of HTML nodes containing the ng-app attribute (also known as an AngularJS directive). When a directive is added to the HTML code, you can execute JavaScript expressions within double curly braces. This technique is useful when angle brackets are being encoded.

Reproduction and proof of concept

  1. Enter an alphanumeric string into the search box.

  2. View the page source and observe that your random string is enclosed in an ng-app directive.

<body ng-app="" class="ng-scope">
...
</body>

  1. Enter the following AngularJS expression in the search box:

{{$on.constructor('alert(1)')()}}

  1. Click search.