decode_prefix6(netdissect_options *ndo,
               const u_char *pd, u_int itemlen, char *buf, u_int buflen)
{
	struct in6_addr addr;
	u_int plen, plenbytes;

	ND_TCHECK(pd[0]);
	ITEMCHECK(1);
	plen = pd[0];
	if (128 < plen)
		return -1;
	itemlen -= 1;

	memset(&addr, 0, sizeof(addr));
	plenbytes = (plen + 7) / 8;
	ND_TCHECK2(pd[1], plenbytes);
	ITEMCHECK(plenbytes);
	memcpy(&addr, &pd[1], plenbytes);
	if (plen % 8) {
		addr.s6_addr[plenbytes - 1] &=
			((0xff00 >> (plen % 8)) & 0xff);
	}
	snprintf(buf, buflen, "%s/%d", ip6addr_string(ndo, &addr), plen);
	return 1 + plenbytes;

trunc:
	return -2;

badtlv:
	return -3;
}

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