Failure to Sanitize Special Elements into a Different Plane (Special Element Injection)

Summary

Cachet is an open source status page system. With Cachet prior to and including 2.4.1, authenticated users, regardless of their privileges (User or Admin), can leak the value of any configuration entry of the dotenv file, e.g. the application secret (`APP_KEY`) and various passwords (email, database, etc). This issue was addressed in the GitHub forked repository https://github.com/fiveai/Cachet by improving `UpdateConfigCommandHandler` and preventing the use of nested variables in the resulting dotenv configuration file. As a workaround, only allow trusted source IP addresses to access to the administration dashboard.