This indicates an attack attempt to exploit a Remote Code Execution Vulnerability in Apple's XNU Operating System Kernel.
The vulnerability is due to an error when the vulnerable software attempts to handle a maliciously crafted request. An attacker can exploit this to execute arbitrary code within the context of the application, via a crafted request.
macOS Sierra 10.12.6 and prior
macOS High Sierra 10.13.6 and prior
Apple iOS 11 and and prior
Apple OS X El Capitan and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.