P-Net before 1.0.3 does not release the Application Relationship (AR) and the RPC session when an RPC request is rejected because its data representation has incorrect endianness. The session and its AR remain allocated, so repeated requests exhaust the available sessions. Once they are exhausted the device no longer answers new RPC requests, including Connect, until it is restarted. A remote unauthenticated attacker can use this to cause a denial of service.