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Install ModSecurity with Nginx on CentOS/RockyLinux/AlmaLinux

What is ModSecurity?

ModSecurity is the most well-known open-source web application firewall (WAF) which was originally built for Apache Web server that provides comprehensive protection for your web applications (like WordPress, Joomla, OpenCart, etc) against a wide range of Layer 7 (HTTP) attacks. ModSecurity can work as the Web Server module and can filter out attacks like SQL injection, cross-site scripting, local file inclusion, etc

cPGuard WAF

cPGuard WAF is a set of ModSecurity rules set that can block most of the generic web attacks against your web applications. It is powered by Malware.Expert Commercial ModSecurity rules for web hosting servers. It is a proprietary set of rules written in-house and provides protection against targeted and automated attacks and has explicit rules to protect CMS like WordPress, Joomla, etc.

Install ModSecurity with Nginx on RHEL based distros

You need to install ModSecurity 3.0 ( libmodsecurity ) to enable ModSecurity module support with your Nginx Web Server. The ModSecurity 3 project is still under rapid development and lacks some features that is available in 2.9.x versions. But ModSecurity 3 is improving and come up with more features in all releases

Step 1. Install Nginx

If you do not have Nginx Web Server installed on your server already, install Nginx using the following command. If you have Nginx installed already, you can ignore this step.

yum install nginx
Step 2 Download and Compile ModSecurity

Install build dependencies using the following commands

yum groupinstall -y "Development Tools"
yum install -y  httpd-devel pcre pcre-devel libxml2 libxml2-devel curl curl-devel openssl openssl-devel

Now you need to download ModSecurity

cd /usr/local/src
git clone --depth 100 -b v3/master --single-branch
cd ModSecurity
git submodule init
git submodule update

Now compile ModSecurity and install it on your server

# Generate configure file
# Pre compilation step. Checks for dependencies
# Compiles the source code
# Installs the Libmodsecurity to **/usr/local/modsecurity/lib/**
make install
Step 3. Download and Compile ModSecurity v3 Nginx Connector Source Code

Run “nginx -V” and notice your Nginx server version. Now you need to download the matching Nginx source code and Nginx Connector Source Code into your server. The use the source code to generate Libmodsecurity module for your Nginx server. Refer following commands and run one by one in order.

mkdir /usr/local/src/cpg
cd /usr/local/src/cpg
#Make sure to change versoin number match it with your local Nginx server version
# Extract the downloaded source code...make sure to use the corerct Nginx version number that you have downloaded 
tar -xvzf nginx-1.21.4.tar.gz
# Download the source code for ModSecurity-nginx connector
git clone
Compile Nginx

Next we need to compile Nginx with ModSecurity module. We will not compile/install Nginx itself but compile the Nginx module only. For this, make sure that your Nginx package is compiled with “–with-compat” flag. The –with-compat flag will make the module binary-compatible with your existing Nginx binary. You can use the following command to compile Nginx + ModSecurity compatible with your existing modules

# Compile the Nginx...make sure to use the corerct Nginx version number that you have downloaded 
cd nginx-1.21.4
./configure --with-compat --with-openssl=/usr/include/openssl/ --add-dynamic-module=/usr/local/src/cpg/ModSecurity-nginx

If your Nginx package is not compatible with “–with-compat” flag, you can check your existing compile flags and use it to build the package. Given below is an example command that you can use for CloudPanel.

# Compile the Nginx...make sure to use the corerct Nginx version number that you have downloaded 
cd nginx-1.21.4
./configure --with-cc-opt='-g -O2 -fdebug-prefix-map=/home/clp/packaging/nginx/tmp/nginx-1.21.4=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -Wdate-time -D_FORTIFY_SOURCE=2' --with-ld-opt='-Wl,-z,relro -Wl,-z,now -fPIC' --prefix=/usr/share/nginx --conf-path=/etc/nginx/nginx.conf --http-log-path=/var/log/nginx/access.log --error-log-path=/var/log/nginx/error.log --lock-path=/var/lock/nginx.lock --pid-path=/run/ --modules-path=/usr/lib/nginx/modules --http-client-body-temp-path=/var/lib/nginx/body --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-proxy-temp-path=/var/lib/nginx/proxy --http-scgi-temp-path=/var/lib/nginx/scgi --http-uwsgi-temp-path=/var/lib/nginx/uwsgi --with-debug --with-pcre-jit --with-http_ssl_module --with-http_stub_status_module --with-http_realip_module --with-http_auth_request_module --with-http_v2_module --with-http_dav_module --with-http_slice_module --with-threads --with-http_addition_module --with-http_geoip_module=dynamic --with-http_gunzip_module --with-http_gzip_static_module --with-http_image_filter_module=dynamic --with-http_sub_module  --with-stream_ssl_module --with-stream_ssl_preread_module --with-mail=dynamic --with-mail_ssl_module  --add-dynamic-module=/usr/local/src/cpg/ModSecurity-nginx

Now we need to build the modules and copy it to the Nginx module directory ( choose the correct modules directory or use the complete path to load the module )

# Generate the module
make modules
# Copy the module to the Nginx module directory
cp -p objs/ /usr/lib64/nginx/modules/
Step4. Load ModSecurity Module into Nginx

Open file /etc/nginx/mod-http-modsecurity.conf and add the following contents to it.

load_module modules/;

Now open /etc/nginx/nginx.conf and add the following line before events tag ( refer the image below for example )

load_module modules/;
Step 5. Install Nginx configuration

1. Open /etc/nginx/conf.d/nginx_modsec.conf and add the following line into it.

modsecurity on;
modsecurity_rules_file /etc/nginx/cpguard-modsecurity.conf;

2. Add the following contents to /etc/nginx/cpguard-modsecurity.conf

SecRuleEngine On
SecRequestBodyAccess On
SecDefaultAction "phase:2,deny,log,status:406"
SecRequestBodyLimitAction ProcessPartial
SecResponseBodyLimitAction ProcessPartial
SecRequestBodyLimit 13107200
SecRequestBodyNoFilesLimit 131072
SecPcreMatchLimit 250000
SecPcreMatchLimitRecursion 250000
SecCollectionTimeout 600
SecDebugLog /var/log/nginx/modsec_debug.log
SecDebugLogLevel 0
SecAuditEngine RelevantOnly
SecAuditLog /var/log/nginx/modsec_audit.log
SecUploadDir /tmp
SecTmpDir /tmp
SecDataDir /tmp
SecTmpSaveUploadedFiles on
# Include file for cPGuard WAF
Include /etc/nginx/cpguard_waf.conf
Step 6. Configure cPGuard WAF Parameters

Once the above steps are completed successfully, you can use the following parameter values in cPGuard Standalone configuration file

waf_server = nginx
waf_server_conf = /etc/nginx/cpguard_waf.conf
waf_server_restart_cmd = /usr/sbin/service nginx restart
waf_audit_log = /var/log/nginx/modsec_audit.log
That’s it

You should have ModSecurity enabled fine and once the cPGuard WAF is enabled, your server is protected against Web Attacks.

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