Apple today released the first Background Security Improvement (BSI) update for macOS Tahoe 26.3.1, iOS 26.3.1, and iPadOS 26.3.1, replacing the rapid security updates used previously. The updates address a WebKit vulnerability that could allow maliciously crafted web content to bypass Same Origin Policy protections. A separate macOS Tahoe 26.3.2 BSI update is available exclusively for the MacBook Neo.

Apple says the vulnerability was fixed through improved input validation. The company tested these security improvements in iOS 26.3, iPadOS 26.3, and macOS Tahoe 26.3 before today's official release. These updates provide additional security protections between major software updates for Safari, WebKit, and other system libraries.

Users can install BSI updates through the Privacy and Security section of Settings, with an option to automatically install them when available. Those who skip BSI updates will receive the fixes in a subsequent standard software update. Apple warns that Background Security Updates may cause rare compatibility issues, in which case they could be temporarily removed and enhanced in another update.