The issue was addressed with improved checks. This issue is fixed in Safari 26.5.2, iOS 26.5.2 and iPadOS 26.5.2, macOS Tahoe 26.5.2. A malicious website may be able to process restricted web content outside the sandbox.
https://isc.sans.edu/diary/rss/33114
https://support.apple.com/en-us/127685