The issue was addressed with improved input validation. This issue is fixed in Safari 18.4, visionOS 2.4, iOS 18.4 and iPadOS 18.4, macOS Sequoia 15.4. A malicious website may be able to claim WebAuthn credentials from another website that shares a registrable suffix.
https://support.apple.com/en-us/122379
https://support.apple.com/en-us/122378