If you look at the Mac security updates lately, you can see avalanches of "execute arbitrary code" fixes for every release. It seems that Mac Os X has more holes than a factory of Swiss cheese.

EDIT: Why was this downvoted?

If you down vote at least you can comment why. These are the security updates since Oct:

https://support.apple.com/en-us/HT201222

https://support.apple.com/en-us/HT208331

https://support.apple.com/en-us/HT208165

https://support.apple.com/en-us/HT208315