In addition to iOS 11.3.1, Apple this afternoon released a macOS High Sierra 10.13.4 security update. As with regular updates, you can find today’s Security Update 2018-001 in the Mac App Store under the Updates tab.

The release notes say that the update addresses two security vulnerabilities related to Crash Reporter and LinkPresentation. The former is a memory corruption issue that allows an application to gain elevated privileges, and the latter is a spoofing issue in the handling of URLs that could lead to UI spoofing. Additionally, a Safari 11.1 update is included with security fixes for WebKit.

Apple recommends that all users install today’s update to improve the security of macOS.

Source: Apple Support