Schneider Electric Modicon TM221CE16R 1.3.3.3 devices allow remote attackers to discover the application-protection password via a \x00\x01\x00\x00\x00\x05\x01\x5a\x00\x03\x00 request to the Modbus port (502/tcp). Subsequently the application may be arbitrarily downloaded, modified, and uploaded.
https://os-s.net/advisories/OSS-2017-01.pdf
http://www.securityfocus.com/bid/97523
http://download.schneider-electric.com/files?p_Doc_Ref=SEVD-2017-097-02