def sanitized_join(path: str, root: pathlib.Path) -> pathlib.Path:
    result = (root / path).absolute()
    if not str(result).startswith(str(root) + "/"):
        raise ValueError("resulting path is outside root")
    return result
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.