It is very simple.
A security researcher found a new bug, which causes crashes of the browser Safari, and a forced restart of the iPhone and iPad. In order to temporarily turn the device into a “brick”, you need a few lines of HTML and CSS.
Information about the new bug shared a Twitter user with the nickname @pwnsdx. There he published a link to the “Safari killer” page that launches the malicious code causes the browser to hang and then force a restart of the entire device.
In comments to the tweet users have begun to give evidence of a temporary disabling of devices running iOS. The bug does not cause serious problems, however, we do not suggest you to experiment with your own iPhone or iPad.
For malicious code, react smartphones and tablets Apple running iOS 7 or newer versions. The bug is present even in the latest builds of the firmware, iOS 11 and 12 iOS.
Unlike other malicious links that trigger on click in iMessage, this you must open the app, able to run HTML code. In other words, the device forcibly reboots, if you go directly to a malicious page in Safari, or if the hacker injects code into the body of the email.
Apple probably already aware of the problem and working on a fix. Probably the bug will fix with the next iOS update.