Window.opener fix bypass

How it was found

Description

Due to a recent report(https://hackerone.com/reports/306414) a fix was deployed in order to resolve the tabnabbing issue. However by using a line break the fix can be bypassed.

Steps to reproduce

1. Browse to your Phabricator instance and create a new document.
2. Now paste in the following content

[[ //google.com | aaa ]] 

and see that there is indeed a rel="noreferer" tag added by clicking preview and then viewing the DOM tree. 3) Now replace the document with the following content:

[[ /
/google.com | aaa ]] 

and see that no tag is added.

Impact

An attacker can abuse this functionality to perform phishing attacks against users