In ZeroMQ libzmq before 4.0.9 4.1.x before 4.1.7 and 4.2.x before 4.3.2 a remote unauthenticated client connecting to a libzmq application running with a socket listening with CURVE encryption/authentication enabled may cause a stack overflow and overwrite the stack with arbitrary data due to a buffer overflow in the library. Users running public servers with the above configuration are highly encouraged to upgrade as soon as possible as there are no known mitigations.