Malicious directory junction can cause WiX RemoveFoldersEx to possibly delete elevated files

Summary

The custom action behind WiX's RemoveFolderEx functionality could allow a standard user to delete protected directories.

Details

RemoveFolderEx deletes an entire directory tree during installation or uninstallation. It does so by recursing every subdirectory starting at a specified directory and adding each subdirectory to the list of directories Windows Installer should delete. If the setup author instructed RemoveFolderEx to delete a per-user folder from a per-machine installer, an attacker could create a directory junction in that per-user folder pointing to a per-machine, protected directory. Windows Installer, when executing the per-machine installer after approval by an administrator, would delete the target of the directory junction.