How to Install ModSecurity with Nginx on Rocky Linux 8

ModSecurity is a popular, free, open-source web application firewall used to protect web applications against several types of attacks including SQL injection, cross-site scripting, and local file inclusion. It is frequently employed to protect websites, cPanel, and other hosting control panels. While ModSecurity was primarily designed for the Apache webserver, it can also work with the Nginx web server.

In this post, we will show you how to install ModSecurity with Nginx on Rocky Linux 8.

Step 1 – Install Required Dependencies

First, you will need to install all required dependencies on your server. You can install all of them with the following command:

dnf install gcc-c++ flex bison yajl curl-devel curl zlib-devel pcre-devel autoconf automake git curl make libxml2-devel pkgconfig libtool httpd-devel redhat-rpm-config git wget openssl openssl-devel vim

dnf --enablerepo=powertools install doxygen yajl-devel -y

Next, install the EPEL and Remi repositories using the following command:

dnf install epel-release https://rpms.remirepo.net/enterprise/remi-release-8.rpm -y

Next, install GeoIP using the following command:

dnf --enablerepo=remi install GeoIP-devel -y

Step 2 – Install ModSecurity

First, download the latest version of ModSecurity using the following command:

git clone --depth 1 -b v3/master --single-branch https://github.com/SpiderLabs/ModSecurity

Next, change the directory to ModSecurity and install the other modules with the following command:

cd ModSecurity
git submodule init
git submodule update

Next, compile and install ModSecurity with the following command:

./build.sh
./configure
make
make install

Step 3 – Install Nginx with LibModsecurity Support

In order to enable LibModsecurity support in Nginx, you will need to compile Nginx with support for LibModsecurity.

First, download the ModSecurity-nginx connector using the following command:

cd ../
git clone https://github.com/SpiderLabs/ModSecurity-nginx.git

Next, download the latest stable version of Nginx with the following command:

wget http://nginx.org/download/nginx-1.19.10.tar.gz

Next, extract the downloaded file using the following command:

tar xzf nginx-1.19.10.tar.gz

Next, create a user for Nginx with the following command:

useradd -r -M -s /sbin/nologin -d /usr/local/nginx nginx

Next, change the directory to the Nginx source and compile it using the following command:

cd nginx-1.19.10
./configure --user=nginx --group=nginx --with-pcre-jit --with-debug --with-http_ssl_module --with-http_realip_module --add-module=/root/ModSecurity-nginx

Next, install it using the following command:

make
make install

Next, copy the sample ModSecurity configuration file and Unicode mapping file with the following command:

cp /root/ModSecurity/modsecurity.conf-recommended /usr/local/nginx/conf/modsecurity.conf
cp /root/ModSecurity/unicode.mapping /usr/local/nginx/conf/

Next, back up the Nginx configuration file:

cp /usr/local/nginx/conf/nginx.conf{,.bak}

Next, edit the Nginx configuration file with the following command:

nano /usr/local/nginx/conf/nginx.conf

Remove all lines and add the following lines:

user  nginx;
worker_processes  1;
pid        /run/nginx.pid;
events {
    worker_connections  1024;
}
http {
    include       mime.types;
    default_type  application/octet-stream;
    sendfile        on;
    keepalive_timeout  65;
    server {
        listen       80;
        server_name  nginx.example.com;
        modsecurity  on;
        modsecurity_rules_file  /usr/local/nginx/conf/modsecurity.conf;
        access_log  /var/log/nginx/access_kifarunix-demo.log;
        error_log  /var/log/nginx/error_kifarunix-demo.log;
        location / {
            root   html;
            index  index.html index.htm;
        }
        error_page   500 502 503 504  /50x.html;
        location = /50x.html {
            root   html;
        }
    }
}

Save and close the file, then create an Nginx log directory:

mkdir /var/log/nginx

Step 4 – Create a Systemd Service File for Nginx

Next, you will need to create a systemd service file to manage the Nginx service. You can create it using the following command:

nano /etc/systemd/system/nginx.service

Add the following lines:

[Unit]
Description=The nginx HTTP and reverse proxy server
After=network.target remote-fs.target nss-lookup.target

[Service]
Type=forking
PIDFile=/run/nginx.pid
ExecStartPre=/usr/bin/rm -f /run/nginx.pid
ExecStartPre=/usr/sbin/nginx -t
ExecStart=/usr/sbin/nginx
ExecReload=/bin/kill -s HUP $MAINPID
KillSignal=SIGQUIT
TimeoutStopSec=5
KillMode=mixed
PrivateTmp=true

[Install]
WantedBy=multi-user.target

Save and close the file, then create a symlink of Nginx binary using the following command:

ln -s /usr/local/nginx/sbin/nginx /usr/sbin/

Next, reload the systemd daemon to apply the changes:

systemctl daemon-reload

Next, start the Nginx service and enable it to start at system reboot:

systemctl enable --now nginx

You can check the status of Nginx with the following command:

systemctl status nginx

You will get the following output:

● nginx.service - The nginx HTTP and reverse proxy server
   Loaded: loaded (/etc/systemd/system/nginx.service; enabled; vendor preset: disabled)
   Active: active (running) since Mon 2021-11-08 09:59:48 UTC; 5s ago
  Process: 73046 ExecStart=/usr/sbin/nginx (code=exited, status=0/SUCCESS)
  Process: 73044 ExecStartPre=/usr/sbin/nginx -t (code=exited, status=0/SUCCESS)
  Process: 73043 ExecStartPre=/usr/bin/rm -f /run/nginx.pid (code=exited, status=0/SUCCESS)
 Main PID: 73048 (nginx)
    Tasks: 2 (limit: 11411)
   Memory: 3.2M
   CGroup: /system.slice/nginx.service
           ├─73048 nginx: master process /usr/sbin/nginx
           └─73049 nginx: worker process

Nov 08 09:59:48 rockylinux systemd[1]: Starting The nginx HTTP and reverse proxy server...
Nov 08 09:59:48 rockylinux nginx[73044]: nginx: the configuration file /usr/local/nginx/conf/nginx.conf syntax is ok
Nov 08 09:59:48 rockylinux nginx[73044]: nginx: configuration file /usr/local/nginx/conf/nginx.conf test is successful
Nov 08 09:59:48 rockylinux systemd[1]: nginx.service: Failed to parse PID from file /run/nginx.pid: Invalid argument
Nov 08 09:59:48 rockylinux systemd[1]: Started The nginx HTTP and reverse proxy server.

Step 5 – Enable ModSecurity Rule

By default, ModSecurity has been configured for detection-only mode, so you will need to enable the ModSecurity rule in the modsecurity.conf file.

You can enable it with the following command:

sed -i 's/SecRuleEngine DetectionOnly/SecRuleEngine On/' /usr/local/nginx/conf/modsecurity.conf

Also, enable the audit log with the following command:

sed -i 's#/var/log/modsec_audit.log#/var/log/nginx/modsec_audit.log#' /usr/local/nginx/conf/modsecurity.conf

Step 6 – Install OWASP ModSecurity Core Rule Set

OWASP provides generic attack detection rules for ModSecurity. You can download it with the following command:

git clone https://github.com/SpiderLabs/owasp-modsecurity-crs.git /usr/local/nginx/conf/owasp-crs

Next, rename the OWASP rule configuration file using the following command:

cp /usr/local/nginx/conf/owasp-crs/crs-setup.conf{.example,}

Next, define the OWASP rule in the ModSecurity configuration file:

echo -e "Include owasp-crs/crs-setup.conf\nInclude owasp-crs/rules/*.conf" >> /usr/local/nginx/conf/modsecurity.conf

Next, restart the Nginx service to apply the changes:

systemctl restart nginx

Step 7 – Verify ModSecurity

At this point, Nginx is installed and configured with ModSecurity support. Now it’s time to test it.

Run the following command injection using the curl command:

curl localhost/index.html?exec=/bin/bash

If everything is fine, you should get the “403 Forbidden” error as shown below:

<html>
<head><title>403 Forbidden</title></head>
<body>
<center><h1>403 Forbidden</h1></center>
<hr><center>nginx/1.19.10</center>
</body>
</html>

You can also verify the ModSecurity log for more information:

tail -100 /var/log/nginx/modsec_audit.log

You should see the following output:

---imefFQJy---D--

---imefFQJy---E--
<html>\x0d\x0a<head><title>403 Forbidden</title></head>\x0d\x0a<body>\x0d\x0a<center><h1>403 Forbidden</h1></center>\x0d\x0a<hr><center>nginx/1.19.10</center>\x0d\x0a</body>\x0d\x0a</html>\x0d\x0a

---imefFQJy---F--
HTTP/1.1 403
Server: nginx/1.19.10
Date: Mon, 08 Nov 2021 10:00:55 GMT
Content-Length: 154
Content-Type: text/html
Connection: keep-alive

---imefFQJy---H--
ModSecurity: Warning. Matched "Operator `PmFromFile' with parameter `unix-shell.data' against variable `ARGS:exec' (Value: `/bin/bash' ) [file "/usr/local/nginx/conf/owasp-crs/rules/REQUEST-932-APPLICATION-ATTACK-RCE.conf"] [line "496"] [id "932160"] [rev ""] [msg "Remote Command Execution: Unix Shell Code Found"] [data "Matched Data: bin/bash found within ARGS:exec: /bin/bash"] [severity "2"] [ver "OWASP_CRS/3.2.0"] [maturity "0"] [accuracy "0"] [tag "application-multi"] [tag "language-shell"] [tag "platform-unix"] [tag "attack-rce"] [tag "paranoia-level/1"] [tag "OWASP_CRS"] [tag "OWASP_CRS/WEB_ATTACK/COMMAND_INJECTION"] [tag "WASCTC/WASC-31"] [tag "OWASP_TOP_10/A1"] [tag "PCI/6.5.2"] [hostname "127.0.0.1"] [uri "/index.html"] [unique_id "1636365655"] [ref "o1,8v21,9t:urlDecodeUni,t:cmdLine,t:normalizePath,t:lowercase"]
ModSecurity: Access denied with code 403 (phase 2). Matched "Operator `Ge' with parameter `5' against variable `TX:ANOMALY_SCORE' (Value: `5' ) [file "/usr/local/nginx/conf/owasp-crs/rules/REQUEST-949-BLOCKING-EVALUATION.conf"] [line "80"] [id "949110"] [rev ""] [msg "Inbound Anomaly Score Exceeded (Total Score: 5)"] [data ""] [severity "2"] [ver "OWASP_CRS/3.2.0"] [maturity "0"] [accuracy "0"] [tag "application-multi"] [tag "language-multi"] [tag "platform-multi"] [tag "attack-generic"] [hostname "127.0.0.1"] [uri "/index.html"] [unique_id "1636365655"] [ref ""]

Conclusion

In the above guide, we explained how to install ModSecurity with Nginx on Rocky Linux 8. Your Nginx web server is now secured with ModSecurity WAF. ModSecurity can protect your server from a wide range of attacks. Get started on VPS hosting from Atlantic.Net today!