int git_delta_read_header(
	size_t *base_out,
	size_t *result_out,
	const unsigned char *delta,
	size_t delta_len)
{
	const unsigned char *delta_end = delta + delta_len;
	if ((hdr_sz(base_out, &delta, delta_end) < 0) ||
		(hdr_sz(result_out, &delta, delta_end) < 0))
		return -1;
	return 0;
}

The product reads data past the end, or before the beginning, of the intended buffer.