GNU Wget 1.12 and earlier uses a server-provided filename instead of the original URL to determine the destination filename of a download, which allows remote servers to create or overwrite arbitrary files via a 3xx redirect to a URL with a .wgetrc filename followed by a 3xx redirect to a URL with a crafted filename, and possibly execute arbitrary code as a consequence of writing to a dotfile in a home directory.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.