Universal XSS with Playlist feature

How it was found

Summary:

Brave iOS has three weaknesses described below. By combining them, Universal XSS can be achieved.

1. Exposure of UserScriptManager.securityToken Playlist.js embeds the exact value of the $<notifyNode> into HTMLVideoElement.prototype.setAttribute. By reading the value, an attacker can retrieve the hidden security token.

2. Exposure of UserScriptManager.messageHandlerToken Also, WindowRenderHelper.js embeds the exact value of the $<handler> into W{securityToken}.postMessage. By reading the value, an attacker can retrieve the hidden message handler token.

3. UXSS in PlaylistHelper through nodeTag PlaylistHelper.swift concatenates strings to build a JavaScript code and executes it on the mainframe of a WebView. Then, nodeTag given from a webpage is directly included in the code. So, if the nodeTag, named as tagId in JS world, passed from the page contained ');alert(document.location);//, unintended alert() is executed on the mainframe.

Products affected:

• Brave iOS 1.32.3 and higher (include the latest Nightly)

Steps To Reproduce:

• Visit the Google page: https://sites.google.com/view/nishimunea-brave-uxss1/page
• This page contains a cross origin malicious page https://csrf.jp/brave/playlist.php in an iframe
• The iframe exploits the above three weaknesses to send a message to playlistHelper
• Push Add to Brave Playlist and Open button in the setting menu
• An alert dialog is appear on the sites.google.com

Supporting Material/References:

• Demonstration movie is attached

Impact

• Universal XSS on the arbitrary domains