A path handling issue was addressed with improved logic. This issue is fixed in Safari 26.3, iOS 18.7.5 and iPadOS 18.7.5, iOS 26.3 and iPadOS 26.3, macOS Sequoia 15.7.5, macOS Sonoma 14.8.4, macOS Tahoe 26.3, visionOS 26.3. A remote user may be able to write arbitrary files.
https://support.apple.com/en-us/126795
https://support.apple.com/en-us/126354
https://support.apple.com/en-us/126353
https://support.apple.com/en-us/126350
https://support.apple.com/en-us/126348