HFS user adding a "web link" in HFS is vulnerable to "target=_blank" exploit
Date: 2025-08
Affected: npm/hfs
Attack vector: info-disclosure
Category: vulnerability-disclosure
Severity: Low
CWE: CWE-1022

### 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: ```<html> <body> <script> window.ope


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