This indicates an attack attempt to exploit an Integer Overflow vulnerability in ZeroMQ.
A remote attacker can exploit this vulnerability by sending a crafted ZMTP 2.0 message to the target server. Successful exploitation could result in the execution of arbitrary code under the security context of the application.
System Compromise: Remote attackers can gain control of vulnerable systems
ZeroMQ libzmq prior to 4.3.1
Refer to the vendor's advisory for updates: