Window.open() and target=”_blank” have a security vulnerability

DanielSeptember 28, 2021January 20, 2023

We often use the HTML target="_blank" or the Javascript window.open() to open pages in new tabs.

// in html
<a href="www.google.com" target="_blank">open google</a>
// in javascript
window.open("www.google.com")

But when the newly opened pages are pointing to a site that we don't know we are opened to a phishing vulnerability. The new page gains some partial access to the linking page with the window.opener object.

For example, it can use the window.opener.location to point the user of the initial page to a fake phishing site that mimics the looks of the original and do all kinds of nasty stuff. This can be very efficient given that the user trusts the page that is already opened.

In order to prevent this we can:

1. in HTML use the rel="noopener" with target="_blank"

<a href="someLink.com" target="_blank" rel="noopener noreferrer">
    open securely in a new tab
</a>

2. in Javascript be sure to reset the "opener" property

const newWindow = window.open("someLink.com");
newWindow.opener = null;

later edit: it seems that noreferrer is now redundant, so noopener should be enough for the HTML use.
later edit 2: we also have access to the windowFeatures parameter for the Window.open(), so we can do:

window.open('https://www.your.url','_blank','noopener')