The issue was addressed with improved memory handling. This issue is fixed in Safari 26.4, iOS 26.4 and iPadOS 26.4, macOS Tahoe 26.4, tvOS 26.4, visionOS 26.4, watchOS 26.4. A malicious website may be able to process restricted web content outside the sandbox.
https://support.apple.com/en-us/126800
https://support.apple.com/en-us/126799
https://support.apple.com/en-us/126798
https://support.apple.com/en-us/126797