Buffer overflow in the handle_packet function in mactelnet.c in the client in MAC-Telnet 0.4.3 and earlier allows remote TELNET servers to execute arbitrary code via a long string in an MT_CPTYPE_PASSSALT control packet.
https://github.com/haakonnessjoen/MAC-Telnet/pull/20
https://github.com/haakonnessjoen/MAC-Telnet/commit/b69d11727d4f0f8cf719c79e3fb700f55ca03e9a