enum delta_result_type do_add_delta(conn *c, item *it, const bool incr,
                                    const int64_t delta, char *buf) {
    char *ptr;
    uint64_t value;
    int res;

    ptr = ITEM_data(it);

    if (!safe_strtoull(ptr, &value)) {
        return NON_NUMERIC;
    }

    if (incr) {
        value += delta;
        MEMCACHED_COMMAND_INCR(c->sfd, ITEM_key(it), it->nkey, value);
    } else {
        if(delta > value) {
            value = 0;
        } else {
            value -= delta;
        }
        MEMCACHED_COMMAND_DECR(c->sfd, ITEM_key(it), it->nkey, value);
    }

    pthread_mutex_lock(&c->thread->stats.mutex);
    if (incr) {
        c->thread->stats.slab_stats[it->slabs_clsid].incr_hits++;
    } else {
        c->thread->stats.slab_stats[it->slabs_clsid].decr_hits++;
    }
    pthread_mutex_unlock(&c->thread->stats.mutex);

    snprintf(buf, INCR_MAX_STORAGE_LEN, "%llu", (unsigned long long)value);
    res = strlen(buf);
    if (res + 2 > it->nbytes) { /* need to realloc */
        item *new_it;
        new_it = do_item_alloc(ITEM_key(it), it->nkey, atoi(ITEM_suffix(it) + 1), it->exptime, res + 2 );
        if (new_it == 0) {
            return EOM;
        }
        memcpy(ITEM_data(new_it), buf, res);
        memcpy(ITEM_data(new_it) + res, "\r\n", 2);
        item_replace(it, new_it);
        do_item_remove(new_it);       /* release our reference */
    } else { /* replace in-place */
        /* When changing the value without replacing the item, we
           need to update the CAS on the existing item. */
        ITEM_set_cas(it, (settings.use_cas) ? get_cas_id() : 0);

        memcpy(ITEM_data(it), buf, res);
        memset(ITEM_data(it) + res, ' ', it->nbytes - res - 2);
    }

    return OK;
}

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.