The attacker is trying to exploit Joomla component called
com_s5clanroster which is vulnerable to SQL Injection.
An SQL injection vulnerability has been reported in Joomla Com
S5clanroster. Successful exploitation of this vulnerability would
allow a remote attacker to execute arbitrary SQL commands on the
That same component was also vulnerable to LFI:
Maybe you don't have that component installed or maybe you are running different CMS, but make sure that you check your website is up-to-date. And not only that, also check if different plugins are still maintained by author, because I saw vulnerable plugins with no updates available from author - and that is consider as a big problem.
Here is another example which can lead to another problem: Expired Domain Leads to WordPress Plugin Redirects
Consider to use ModSecurity (Open Source Web Application Firewall). How to?