bool IsLink(const FilePath& file_path) {
  stat_wrapper_t st;
  if (CallLstat(file_path.value().c_str(), &st) != 0)
    return false;

  if (S_ISLNK(st.st_mode))
    return true;
  else
    return false;
}

The product 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 product 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.