P-Net: RPC sessions leak, letting attackers stop devices answering connections

P-Net before 1.0.4 keeps the RPC session that is allocated for a fragment of a request with an unknown activity UUID, without a timeout, when the rest of the request never arrives. A session that does not get an Application Relationship is also kept after the response. Repeated fragments or requests with different activity UUIDs exhaust the available sessions, one UDP packet per session. Once they are exhausted the device no longer answers a Connect request until it is restarted. An unauthenticated attacker with ADJACENT network access can use this to cause a denial of service.