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

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Submitted by falko (Contact Author) (Forums) on Mon, 2012-08-06 17:41. :: Web Server | nginx | Security

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

Version 1.0
Author: Falko Timme <ft [at] falkotimme [dot] com>
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Last edited 07/26/2012

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.

I do not issue any guarantee that this will work for you!

 

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:

/etc/init.d/nginx reload

 

Links

 

About The Author

Falko Timme is the owner of nginx WebhostingTimme 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".


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Comments will be published after administrator approval.
Submitted by Anonymous (not registered) on Thu, 2012-08-09 14:38.

The article is a poor solution to the problem they are trying to tackle.  The better answer is to use naxsi, the application firewall for nginx.

 

Submitted by ViruSzZ (not registered) on Thu, 2012-08-09 09:56.

hey, those are really great tips for additionally securing my nginx server.

was wondering if there's anywhere online to read more deeply about all this options ?

thanks,

 - d

Submitted by MrOwen (not registered) on Tue, 2012-08-07 01:48.

Great rulesets!

If I'm not mistaken, these rules can be added to a separate config file and then included for each server block (I feel nginx would allow this). Another thing; I've come across many resources regarding the use of conditional "ifs" in the nginx config and it seems the overwhelming majority of them strongly discourage the use of it citing a hit on performance (they suggest using try_files or something similar but, obviously, that isn't applicable here so perhaps these if statements are a "necessary evil" in terms of optimizing a config).