gix-worktree-state specifies 0777 permissions when checking out executable files, intending that the umask will restrict them appropriately. But one of the strategies it uses to set permissions is not subject to the umask. This causes files in a repository to be world-writable in some situations.
During checkout, gitoxide does not verify that paths point to locations in the working tree. A specially crafted repository can, when cloned, place new files anywhere writable by the application.
On Windows, fetching refs that clash with legacy device names reads from the devices, and checking out paths that clash with such names writes arbitrary data to the devices. This allows a repository, when cloned, to cause indefinite blocking or the production of arbitrary message that appear to have come from the application, and potentially other harmful effects under limited circumstances.