https://perishablepress.com/wordpress-blank-target-vulnerability/
For those who haven’t yet noticed, WordPress now adds rel=”noopener” attributes for any external links added via the link Quicktag in the Visual/RTE. So if you enable the option, “Open link in a new tab”, WordPress automatically will add the rel noopener attribute to the link. This is to protect against CORS and other exploits that take advantage of
Source: Security Feed