MQTT implementation in Sungrow iSolarCloud allowed users to subscribe to all data of all connected inverters

Summary

SunGrow's back end users system iSolarCloud https://isolarcloud.com  uses an MQTT service to transport data from the user's connected devices to the user's web browser.  The MQTT server however did not have sufficient restrictions in place to limit the topics that a user could subscribe to.  While the data that is transmitted through the MQTT server is encrypted and the credentials for the MQTT server are obtained though an API call, the credentials could be used to subscribe to any topic and the encryption key can be used to decrypt all messages received. An attack with an account on iSolarCloud.com could extract MQTT credentials and the decryption key from the browser and then use an external program to subscribe to the topic '#' and thus recieve all messages from all connected devices.