Apple today released an update to their major platforms. There are no new features, but in it are 2 security updates, both for things being actively exploited in the wild since February, reportedly by the NSO group, which is the same one that is responsible for the Pegasus malware.
One is for a WebKit engine, that powers Safari and several other web view items in iOS and Mac OS. The other is an issue with the CoreGraphics functionality, the engine that drives some of the graphical functionality on these devices.
If you’re running Mac OS Catalina or Mojave, you’ll also need to update. There will be a Safari update to address the WebKit vulnerability, but the CoreGraphics vulnerability is only in Catalina at the time.
It is highly recommended you update as soon as possible on your devices. You can read the full info on Apple’s website: https://support.apple.com/en-us/HT201222