According to its self-reported version number, the Joomla! installation running on the remote web server is prior to 3.8.8. It is, therefore, affected by a multiple vulnerabilities. Note that Nessus has not attempted to exploit these issues but has instead relied only on the application's self-reported version number.
Joomla! Core Multiple Vulnerabilities-02 May18 (20180507/20180505/20180504)
Joomla! Core Multiple Vulnerabilities-01 May18 (20180502/20180501)
Joomla! Core 'Unpublished Tags' Information Disclosure Vulnerability (20180503)
Joomla! Core 'com_fields' Remote Code Execution Vulnerability (20180506)
 - Core - Information Disclosure about unpublished tags
 - Core - Installer leaks plain text password to local user
 - Core - Filter field in com_fields allows remote code execution