People using target='_blank' links usually have no idea about this curious fact:

The page we're linking to gains partial access to the linking page via the window.opener object.

The newly opened tab can then change the window.opener.location to some phishing page. Users trust the page that is already opened, they won't get suspicious.

Example attack scenario

Create a fake "viral" page with cute cat pictures, jokes or whatever, get it shared on Facebook (which is known for opening links via _blank).

Create a "phishing" website at https://fakewebsite/facebook.com/page.html for example

for example Put this code on your "viral" page window.opener.location = 'https://fakewebsite/facebook.com/page.html'; which redirects the Facebook tab to your phishing page, asking the user to re-enter her Facebook password.

How to fix

Add this to your outgoing links.

rel="noopener"

Update: FF does not support "noopener" so add this.

rel="noopener noreferrer"

Remember, that every time you open a new window via window.open(); you're also "vulnerable" to this, so always reset the "opener" property

var newWnd = window.open(); newWnd.opener = null;

PS. Interestingly, Google doesn't seem to care.



Alex Yumashev

Alex has founded Jitbit in 2005 and is a software engineer passionate about customer support.

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