This indicates an attack attempt against a Buffer Overflow vulnerability in LibVNCClient.
A remote attacker can exploit this vulnerability by sending a maliciously crafted RFB response to a client that uses libVNCClient library. At the worst case, successful exploitation may result in remote code execution.
LibVNCClient prior to commit 7b1ef0ffc4815cab9a96c7278394152bdc89dc4d
System Compromise: Remote attackers can gain control of vulnerable systems
Apply the latest patch from the vendor: