Kaspersky: Opening up a Universal XSS vulnerability in Microsoft Edge

ID H1:463915
Type hackerone
Reporter palant
Modified 2019-08-28T17:54:25


Summary In Microsoft Edge, URL Advisor UI is served as first-party content on every domain. So the XSS vulnerability I found in this UI automatically applies to all websites, it allows running code in the context of any domain.

Description URL Advisor frame is located under https://www.google.com/<INJECT_ID>/ua/url_advisor_balloon.html and https://www.yahoocom/<INJECT_ID>/ua/url_advisor_balloon.html in Microsoft Edge (always the same INJECT_ID value). It gets its content from a message sent via window.postMessage() without validating message origin. Under some circumstances it will assign that data as link target, so a malicious website can make that link point to a javascript: URL. Clickjacking then allows making the user click that link - while sites like google.com use X-Frame-Options header to disallow framing, no such restrictions are in place for the url_advisor_balloon.html frame.

Environment - Scope: Application - Product name: Kaspersky Internet Security - Product version: - OS name and version (incl SP): Windows 10.0.17134 - Attack type: Universal XSS - Maximum user privileges needed to reproduce your issue: no privileges

Steps to reproduce 1. Download attached server.py and universal_xss.html to some directory on your computer and run server.py (Python 3 required). This is a very rudimentary HTTP server running on http://localhost:5000/, you could use some other web server as well. 2. Edit the file %WINDIR%\sysnative\drivers\etc\hosts as administrator and add the following line: www.google.example.com. Normally, you would just use a subdomain of a domain you own - the host name has to start with "www.google." for URL Advisor to apply to it. 3. Open Microsoft Edge and go to http://www.google.example.com:5000/universal_xss.html 4. As advised by the page, move your mouse and click somewhere on the page.

You will see an alert message saying: "Hi, this is JavaScript code running on www.google.com." That's the result of the code alert('Hi, this JavaScript code is running on ' + document.domain) executing in the context of the Google website. Injecting code into any other domain would have been easily possible as well.

Recommendation This user interface should never be served as first-party, even once the vulnerability here is fixed. Any XSS vulnerability in Kaspersky code automatically elevates to Universal XSS otherwise, this is too dangerous. Frankly, I don't see why it is done in this way with Microsoft Edge - in Firefox and Internet Explorer the same UI is always served via kis.v2.scr.kaspersky-labs.com, so vulnerabilities here don't affect other websites.


A malicious website can easily make users click by pretending to be a game. And while the user clicks, they will be allowing the attackers to inject code into various internet domains and exfiltrating data in the background.