local int complain(char *fmt, ...)
{
    va_list ap;

    if (g.verbosity > 0) {
        fprintf(stderr, "%s: ", g.prog);
        va_start(ap, fmt);
        vfprintf(stderr, fmt, ap);
        va_end(ap);
        putc('\n', stderr);
        fflush(stderr);
    }
    return 0;
}

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.