The get1 command, as used by lftpget, in LFTP before 4.0.6 does not properly validate a server-provided filename before determining the destination filename of a download, which allows remote servers to create or overwrite arbitrary files via a Content-Disposition header that suggests 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.