def is_subpath(path, root):
    root = os.path.realpath(root)
    path = os.path.realpath(os.path.join(root, path))
    # join() is used below to ensure root ends with a slash
    return path.startswith(os.path.join(root, ''))
The software uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the software does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.