Researcher devised a new CSS & HTML attack that causes iPhone reboot or freezes Macs

Pierluigi Paganini September 16, 2018

The security researcher Sabri Haddouche from Wire devised a new CSS attack that causes iPhone reboot or freezes Macs.

The security researcher Sabri Haddouche from Wire devised a new attack method that saturates Apple device’s resources and causing it crashes or system restarts when visiting a web page. The experts discovered that iOS restart and macOS freezes when the user visits a web page that contains certain CSS & HTML.

Depending on the version of iOS being used, the bug could trigger the UI restart, cause a kernel panic and consequent device reboot.

This attack leverages a weakness in the -webkit-backdrop-filter CSS, for this reason, it affects all browsers on iOS that leverage on WebKit as rendering engine is WebKit. The weakness also affects Safari and Mail in macOS, but it doesn’t affect Linux and Windows systems.

“The attack exploits a weakness in the –webkit-backdrop-filter CSS property,” Haddouche explained to BleepingComputer. “By using nested divs with that property, we can quickly consume all graphic resources and crash or freeze the OS. The attack does not require Javascript to be enabled therefore it also works in Mail. On macOS, the UI freeze. On iOS, the device restart.”


Haddouche successfully tested the attack on iOS 12 and caused the device to reboot, on iOS 11.4.1 it only caused a UI restart.

Haddouche explained that on macOS, the attack will only cause Mail and Safari to freeze for a second and then slow down the computer.

Haddouche also devised another attack that uses HTML, CSS, and JavaScript to completely freeze macOS systems. The researchers told Bleeping Computer that he has not disclosed it because it persists after reboot and macOS will relaunch Safari with the malicious page, causing the system entering in a look that freeze it again.

Lawrence Abrams from Bleeping Computer created a video showing what happens when a user visits the attack page created by Haddouche (sees the rawgit[.]com) and published on Github. Lawrence used an iPhone running iOS 11.4.1.

The bad news is that there is no mitigation for this attack.

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Pierluigi Paganini

(Security Affairs – iPhone reboot, CSS attack)

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