This indicates an attack attempt to exploit a Use After Free Vulnerability in Apple Webkit.
The vulnerability is due to an error when the vulnerable software handles a maliciously crafted webpage. A remote attacker may be able to exploit this to execute arbitrary code, via a crafted webpage.
Apple iOS before 10.3.3
Apple Safari before 10.1.2
Apple iCloud before 6.2.2 on Windows
Apple iTunes before 12.6.2 on Windows
Apple tvOS before 10.2.2
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.