The vulnerability hits the WebKit rendering engine used in Safari by applying a CSS effect -- "backdrop-filter" -- that requires enough heavy graphics processing to cause iOS to crash completely.
Software engineer and security researcher Sabri Haddouche, who works for encrypted messaging app Wire, discovered the vulnerability and shared videos of its effects on Twitter. Haddouche also discussed his findings with ZDNet:
"By using nested divs with that property, we can quickly consume all graphic resources and freeze or kernel panic the OS."
Haddouche didn't publish the modified macOS vulnerability because once the computer reboots, Safari persists and the browser is automatically launched again with the same result, resulting in a cycle of reboots. The researcher says that he discovered the vulnerabilities during research for denial of service bugs on different web browsers.