This indicates an attack attempt to exploit an Information Disclosure Vulnerability in Mitsubishi Electric ME-RTU devices.
The vulnerability is due to improper authentication in the application. A remote attacker can exploit this to access sensitive information, such as configuration and admin credentials, on the affected devices.
Mitsubishi Electric ME-RTU devices through 2.02 and INEA ME-RTU devices through 3.0
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems
Currently we are unaware of any vendor supplied patch for this issue.