static void process_bin_append_prepend(conn *c) {
    char *key;
    int nkey;
    int vlen;
    item *it;

    assert(c != NULL);

    key = binary_get_key(c);
    nkey = c->binary_header.request.keylen;
    vlen = c->binary_header.request.bodylen - nkey;

    if (settings.verbose > 1) {
        fprintf(stderr, "Value len is %d\n", vlen);
    }

    if (settings.detail_enabled) {
        stats_prefix_record_set(key, nkey);
    }

    it = item_alloc(key, nkey, 0, 0, vlen+2);

    if (it == 0) {
        if (! item_size_ok(nkey, 0, vlen + 2)) {
            write_bin_error(c, PROTOCOL_BINARY_RESPONSE_E2BIG, vlen);
        } else {
            write_bin_error(c, PROTOCOL_BINARY_RESPONSE_ENOMEM, vlen);
        }
        /* swallow the data line */
        c->write_and_go = conn_swallow;
        return;
    }

    ITEM_set_cas(it, c->binary_header.request.cas);

    switch (c->cmd) {
        case PROTOCOL_BINARY_CMD_APPEND:
            c->cmd = NREAD_APPEND;
            break;
        case PROTOCOL_BINARY_CMD_PREPEND:
            c->cmd = NREAD_PREPEND;
            break;
        default:
            assert(0);
    }

    c->item = it;
    c->ritem = ITEM_data(it);
    c->rlbytes = vlen;
    conn_set_state(c, conn_nread);
    c->substate = bin_read_set_value;
}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.