HFS user adding a "web link" in HFS is vulnerable to "target=_blank" exploit

Summary

When adding a "web link" to the HFS virtual filesystem, the frontend opens it with target="_blank" but without the rel="noopener noreferrer" attribute. This allows the opened page to use the window.opener property to change the location of the original HFS tab.

Details

While most modern browsers have fixes already implemented for this target="_blank" exploit at the browser level, users on outdated browsers remain vulnerable. This means that if an admin of the HFS instance adds a link to an external third-party service (that they believe is safe at the time) and that service they added later becomes compromised, the malicious page could replace the original HFS tab's content with a phishing page. This does not require the admin account itself to be compromised, only that a legitimate linked site turns malicious.

Impact

Affected users (people using old browsers without the browser level fix) could be misled into entering their HFS credentials or other sensitive information into a fake site controlled by an attacker. This vulnerability is fixed in most modern browsers, but adding rel="noopener noreferrer" remains a best practice to protect legacy environments.

PoC

Firstly, in the HFS admin page, under the filesystem (/~/admin/#/fs) press "Add" then "web link" then set the link to take the user to to an HTML file that exploits this vulnerability, here is an example of a malicious HTML file's code:

 <body>
  <script>
    window.opener.location = "https://example.org";
  </script>
<b>Error loading...</b>
 </body>
</html>

Now, in the HFS folder you placed this web link in, open HFS and click the web link, if you aren't on a modern browser that fixed this vulnerability on the browser level, then switch back to the HFS tab that opened it, and you should be taken to "https://example.org" if you tried the code I provided, or whatever other page you tried.