The handle_request function in lib/HTTPServer.pm in Monitorix before 3.3.1 allows remote attackers to execute arbitrary commands via shell metacharacters in the URI.
https://github.com/mikaku/Monitorix/issues/30
https://github.com/mikaku/Monitorix/commit/ff80441be7089f774448dfe4b49e6fced70e71cb