CVE-2020-28349: Improper Input Validation

** DISPUTED ** An inaccurate frame deduplication process in ChirpStack Network Server allows a malicious gateway to perform uplink Denial of Service via malformed frequency attributes in CollectAndCallOnceCollect in internal/uplink/collect.go. NOTE: The vendor’s position is that there are no “guarantees that allowing untrusted LoRa gateways to the network should still result in a secure network.”