A developer named Sabri invented a crash for any iOS and non iOS device that has a safari browser on board. He used just pure html and css for it and many people claim it even works on other platforms. The way how it works is safari can’t render the css inside the html file and it forces the phone to restart springboard(the ui part of the iOS) and it can have different outcomes on other devices. In comparison to other crashes and hacks that we had in the past with the iOS, this is definitely not the most harmful hack, as it only affects the visual part of the iOS. Its also important to be careful when opening emails, as someone can embed this into email.
Link to the tweet (link to crash is in it, be careful opening it): https://twitter.com/pwnsdx/status/1040944750973595649