This indicates an attack attempt to exploit a Cross Site Scripting vulnerability in Apple MacOS.
The vulnerability is due to an error when the vulnerable software attempts to handle a maliciously crafted request. An attacker can exploit this by tricking a user into viewing the data and execute arbitrary script code within the context of the application.
Apple MacOS 10.12.2 and previous versions.
System Compromise: Remote attackers can execute arbitrary script code within the context of the target user
Apply the most recent upgrade or patch from the vendor.