While macOS 15.4 is still in beta testing, Apple has released a second small update to macOS 15.3 with an important security fix.
The release notes don’t offer any clues as to what the bug fixes are, but Apple’s security update page explains the patch. The issue, which affects the WebKit engine, is a “supplementary fix” for an attack that was previously blocked in iOS 17.2, which was released in December 2023. According to Apple, the flaw may have been exploited in “an extremely sophisticated attack against specific targeted individuals” using versions prior to iOS 17.2.
Apple released macOS Sonoma 14.2, Ventura 13.6.3, and Monterey 12.7.2 alongside iOS 17.2, though it’s unclear which patch this specifically refers to. Apple describes the flaw as an out-of-bounds write issue, which was addressed with improved checks to prevent unauthorized actions.
You can update your Mac by heading over to System Settings, and then select General and Software Update.