nginx: How To Block Exploits, SQL Injections, File Injections, Spam, User Agents, Etc.

This short article explains how you can block the most common exploits, SQL injections, file injections, spam and user agents used by hackers and bandwidth hoggers from your nginx vhosts with some simple configuration directives. This configuration is far from being complete, but it's a good starting point. You will have to watch your logs for attempted break-in attempts and then try to modify/complete the ruleset.

Modify Your Nginx Vhosts

The ruleset I use here has to be inserted in each nginx vhost (inside a server {} container) where you want to use it. Unfortunately, it can't be used globally because the set directive is not allowed inside the http {} container.

server {
[...]

    ## Block SQL injections
    set $block_sql_injections 0;
    if ($query_string ~ "union.*select.*\(") {
        set $block_sql_injections 1;
    }
    if ($query_string ~ "union.*all.*select.*") {
        set $block_sql_injections 1;
    }
    if ($query_string ~ "concat.*\(") {
        set $block_sql_injections 1;
    }
    if ($block_sql_injections = 1) {
        return 403;
    }

    ## Block file injections
    set $block_file_injections 0;
    if ($query_string ~ "[a-zA-Z0-9_]=http://") {
        set $block_file_injections 1;
    }
    if ($query_string ~ "[a-zA-Z0-9_]=(\.\.//?)+") {
        set $block_file_injections 1;
    }
    if ($query_string ~ "[a-zA-Z0-9_]=/([a-z0-9_.]//?)+") {
        set $block_file_injections 1;
    }
    if ($block_file_injections = 1) {
        return 403;
    }

    ## Block common exploits
    set $block_common_exploits 0;
    if ($query_string ~ "(<|%3C).*script.*(>|%3E)") {
        set $block_common_exploits 1;
    }
    if ($query_string ~ "GLOBALS(=|\[|\%[0-9A-Z]{0,2})") {
        set $block_common_exploits 1;
    }
    if ($query_string ~ "_REQUEST(=|\[|\%[0-9A-Z]{0,2})") {
        set $block_common_exploits 1;
    }
    if ($query_string ~ "proc/self/environ") {
        set $block_common_exploits 1;
    }
    if ($query_string ~ "mosConfig_[a-zA-Z_]{1,21}(=|\%3D)") {
        set $block_common_exploits 1;
    }
    if ($query_string ~ "base64_(en|de)code\(.*\)") {
        set $block_common_exploits 1;
    }
    if ($block_common_exploits = 1) {
        return 403;
    }

    ## Block spam
    set $block_spam 0;
    if ($query_string ~ "\b(ultram|unicauca|valium|viagra|vicodin|xanax|ypxaieo)\b") {
        set $block_spam 1;
    }
    if ($query_string ~ "\b(erections|hoodia|huronriveracres|impotence|levitra|libido)\b") {
        set $block_spam 1;
    }
    if ($query_string ~ "\b(ambien|blue\spill|cialis|cocaine|ejaculation|erectile)\b") {
        set $block_spam 1;
    }
    if ($query_string ~ "\b(lipitor|phentermin|pro[sz]ac|sandyauer|tramadol|troyhamby)\b") {
        set $block_spam 1;
    }
    if ($block_spam = 1) {
        return 403;
    }

    ## Block user agents
    set $block_user_agents 0;

    # Don't disable wget if you need it to run cron jobs!
    #if ($http_user_agent ~ "Wget") {
    #    set $block_user_agents 1;
    #}

    # Disable Akeeba Remote Control 2.5 and earlier
    if ($http_user_agent ~ "Indy Library") {
        set $block_user_agents 1;
    }

    # Common bandwidth hoggers and hacking tools.
    if ($http_user_agent ~ "libwww-perl") {
        set $block_user_agents 1;
    }
    if ($http_user_agent ~ "GetRight") {
        set $block_user_agents 1;
    }
    if ($http_user_agent ~ "GetWeb!") {
        set $block_user_agents 1;
    }
    if ($http_user_agent ~ "Go!Zilla") {
        set $block_user_agents 1;
    }
    if ($http_user_agent ~ "Download Demon") {
        set $block_user_agents 1;
    }
    if ($http_user_agent ~ "Go-Ahead-Got-It") {
        set $block_user_agents 1;
    }
    if ($http_user_agent ~ "TurnitinBot") {
        set $block_user_agents 1;
    }
    if ($http_user_agent ~ "GrabNet") {
        set $block_user_agents 1;
    }

    if ($block_user_agents = 1) {
        return 403;
    }
[...]
}

Whenever one of the rules matches a request, a 403 Forbidden error is returned to the client. I've commented out the wget rule here because this would also block cron jobs that use wget which is quite common among modern CMS applications. If your application doesn't use wget, you can uncomment that rule as well.

Don't forget to reload nginx:

service nginx reload

ISPConfig Nginx Servers

These rules can also be used in the Nginx Directives field in ISPConfig. Just paste the rules into the Nginx Directives field on the website options tab in ISPConfig, without the surrounding server { ... } block. The nginx reload is applied by ISPConfig automatically when you save the changes.

Links

• nginx: http://nginx.org/

About The Author

Falko Timme is the owner of Timme Hosting (ultra-fast nginx web hosting). He is the lead maintainer of HowtoForge (since 2005) and one of the core developers of ISPConfig (since 2000). He has also contributed to the O'Reilly book "Linux System Administration".