Actually, it's even in the logs:
.2016-04-15 17:02:23: ClientTCPSocket.cpp(1969): Remote Client Protocol: Packet with protocol c5, opcode 85, size 421 received from ...
But statistics indicate that for protocol c5 (OP_EMULEPROT) and opcode 85 (OP_PUBLICKEY) the size should always be 77. And also according to the source, size 421 (which agrees with the size given in the packet header) definitely isn't allowed for this type of packet. Brief, some remote client sends a malformed packet with protocol c5, opcode 85.
Question to the adepts: What should be done with such a defective packet? How to discard it cleanly?