Which to me is a big yawn because as long as we have javascript engines in our browsers this will probably be possible. Browsing websites is basically an RCE anyway.
https://www.cultofmac.com/53323/jailbreakme-2-0-jailbreaks-i...
Edit: I use ‘letting’ above loosely meaning that the specific website mentioned allowed the visitor to control whether the exploit was actually executed or not.