This indicates an attack attempt to exploit a Use After Free vulnerability in WebKit, a component of Apple Safari.
The vulnerability is due to an error when the vulnerable software handles a maliciously crafted web page. An attacker can exploit this by tricking an unsuspecting user into visiting a malicious webpage and execute arbitrary code within the context of the application.
WebKit in Apple iOS before 12.2
WebKit in macOS before 10.14.4
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.