A validation issue existed in the handling of symlinks. This issue was addressed with improved validation of symlinks. This issue is fixed in iOS 12.3, macOS Mojave 10.14.5, tvOS 12.3, watchOS 5.2.1. A local user may be able to modify protected parts of the file system.
https://support.apple.com/HT210122
https://support.apple.com/HT210120