A new attack has been discovered that will cause iOS to restart or respring and macOS to freeze simply by visiting a web page that contains certain CSS & HTML. Windows and Linux users are not affected by this bug.
This new attack was discovered by Sabri Haddouche, a security researcher at Wire, who was able to devise a way to quickly use up an Apple device’s resources so that it crashes when visiting a web page.
This attack affects all browsers on iOS, as well as Safari and Mail in macOS, because they all use the WebKit rendering engine.
Source: Bleeping Computer