Learn How To Install ModSecurity for Nginx on CentOS 7, Debian 8, and Ubuntu 16.04

March 8, 2019

Table of Contents

ModSecurity is an open source web application firewall (WAF) module which is great for protecting Apache, Nginx, and IIS from various cyber attacks that target potential vulnerabilities in various web applications

In this article, we will install and configure ModSecurity for Nginx on CentOS 7, Debian 8, and Ubuntu 16.04.


https://www.itweb.services/tutorials/linux-guides/how-to-update-centos-7-ubuntu-16-04-and-debian-8″>up-to-date installation of CentOS 7, Debian 8, or Ubuntu 16.04 64-bit.

  • Logging in as root.
  • Step 1: Update the system

    https://www.itweb.services/tutorials/linux-guides/how-to-update-centos-7-ubuntu-16-04-and-debian-8″>this guide, update your server’s Kernel and Packages to the latest available version.

    Step 2: Install dependencies

    Before you can compile Nginx and ModSecurity successfully, you need to install several software packages as follows.

    a) On CentOS 7:

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

    b) On Debian 8 or Ubuntu 16.04:

    apt-get install -y git build-essential libpcre3 libpcre3-dev libssl-dev libtool autoconf apache2-dev libxml2-dev libcurl4-openssl-dev automake pkgconf

    Step 3: Compile ModSecurity

    Due to several instabilities reported on ModSecurity for Nginx master branch, for now, it is officially recommended to use the latest version of the nginx_refactoring branch whenever possible.

    Download the nginx_refactoring branch of ModSecurity for Nginx:

    cd /usr/src
    git clone -b nginx_refactoring https://github.com/SpiderLabs/ModSecurity.git

    Compile ModSecurity:

    a) On CentOS 7:

    cd ModSecurity
    sed -i '/AC_PROG_CC/aAM_PROG_CC_C_O' configure.ac
    sed -i '1 iAUTOMAKE_OPTIONS = subdir-objects' Makefile.am
    ./configure --enable-standalone-module --disable-mlogc

    Note: the two sed commands above are used to prevent warning messages when using newer
    automake versions.

    b) On Debian 8 or Ubuntu 16.04:

    cd ModSecurity
    ./configure --enable-standalone-module --disable-mlogc

    Step 4: Compile Nginx

    Download and unarchive the latest stable release of Nginx which is Nginx 1.10.3 at the time of writing:

    cd /usr/src
    wget https://nginx.org/download/nginx-1.10.3.tar.gz
    tar -zxvf nginx-1.10.3.tar.gz && rm -f nginx-1.10.3.tar.gz

    a) On CentOS 7:

    First, you need to create a dedicated user nginx and a dedicated group nginx for Nginx:

    groupadd -r nginx
    useradd -r -g nginx -s /sbin/nologin -M nginx

    Then compile Nginx while enabling ModSecurity and SSL modules:

    cd nginx-1.10.3/
    ./configure --user=nginx --group=nginx --add-module=/usr/src/ModSecurity/nginx/modsecurity --with-http_ssl_module
    make install

    Modify the default user of Nginx:

    sed -i "s/#user  nobody;/user nginx nginx;/" /usr/local/nginx/conf/nginx.conf

    b) On Debian 8 or Ubuntu 16.04:

    First, you should use the existing user www-data and the existing group www-data.

    Then compile Nginx while enabling ModSecurity and SSL modules:

    cd nginx-1.10.3/
    ./configure --user=www-data --group=www-data --add-module=/usr/src/ModSecurity/nginx/modsecurity --with-http_ssl_module
    make install

    Modify the default user of Nginx:

    sed -i "s/#user  nobody;/user www-data www-data;/" /usr/local/nginx/conf/nginx.conf

    Having Nginx successfully installed, related files will be located at:

    nginx path prefix: "/usr/local/nginx"
    nginx binary file: "/usr/local/nginx/sbin/nginx"
    nginx modules path: "/usr/local/nginx/modules"
    nginx configuration prefix: "/usr/local/nginx/conf"
    nginx configuration file: "/usr/local/nginx/conf/nginx.conf"
    nginx pid file: "/usr/local/nginx/logs/nginx.pid"
    nginx error log file: "/usr/local/nginx/logs/error.log"
    nginx http access log file: "/usr/local/nginx/logs/access.log"
    nginx http client request body temporary files: "client_body_temp"
    nginx http proxy temporary files: "proxy_temp"
    nginx http fastcgi temporary files: "fastcgi_temp"
    nginx http uwsgi temporary files: "uwsgi_temp"
    nginx http scgi temporary files: "scgi_temp"

    you can test the installation with:

    /usr/local/nginx/sbin/nginx -t

    If nothing goes wrong, the output should be:

    nginx: the configuration file /usr/local/nginx/conf/nginx.conf syntax is ok
    nginx: configuration file /usr/local/nginx/conf/nginx.conf test is successful

    For your convenience, you can setup a systemd unit file for Nginx:

    cat <<EOF>> /lib/systemd/system/nginx.service
    ExecStartPre=/usr/local/nginx/sbin/nginx -t -c /usr/local/nginx/conf/nginx.conf
    ExecStart=/usr/local/nginx/sbin/nginx -c /usr/local/nginx/conf/nginx.conf
    ExecReload=/usr/local/nginx/sbin/nginx -s reload
    KillStop=/usr/local/nginx/sbin/nginx -s stop

    Moving forward, you can start/stop/restart Nginx as follows:

    systemctl start nginx.service
    systemctl stop nginx.service
    systemctl restart nginx.service

    Step 4: Configure ModSecurity and Nginx

    4.1 Configure Nginx:

    vi /usr/local/nginx/conf/nginx.conf

    Find the following segment within the http {} segment:

    location / {
        root   html;
        index  index.html index.htm;

    Insert the below lines into the location / {} segment:

    ModSecurityEnabled on;
    ModSecurityConfig modsec_includes.conf;
    #proxy_pass http://localhost:8011;
    #proxy_read_timeout 180s;

    The final result should be:

    location / {
        ModSecurityEnabled on;
        ModSecurityConfig modsec_includes.conf;
        #proxy_pass http://localhost:8011;
        #proxy_read_timeout 180s;
        root   html;
        index  index.html index.htm;

    Save and quit:


    Note: The Nginx config above is only a sample config for using Nginx as a web server rather than a reverse proxy. If you are using Nginx as a reverse proxy, remove the # character in last two lines and make appropriate modifications to them.

    4.2 Create a file named /usr/local/nginx/conf/modsec_includes.conf:

    cat <<EOF>> /usr/local/nginx/conf/modsec_includes.conf
    include modsecurity.conf
    include owasp-modsecurity-crs/crs-setup.conf
    include owasp-modsecurity-crs/rules/*.conf

    Note: The config above will apply all of the OWASP ModSecurity Core Rules in the owasp-modsecurity-crs/rules/ directory. If you want to apply selective rules only, you should remove the include owasp-modsecurity-crs/rules/*.conf line, and then specify exact rules you need after step 4.5.

    4.3 Import ModSecurity configuration files:

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

    4.4 Modify the /usr/local/nginx/conf/modsecurity.conf file:

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

    4.5 Add OWASP ModSecurity CRS (Core Rule Set) files:

    cd /usr/local/nginx/conf
    git clone https://github.com/SpiderLabs/owasp-modsecurity-crs.git
    cd owasp-modsecurity-crs
    mv crs-setup.conf.example crs-setup.conf
    cd rules

    Step 5: Test ModSecurity

    Start Nginx:

    systemctl start nginx.service

    Open port 80 in order to allow outside access:

    a) On CentOS 7:

    firewall-cmd --zone=public --permanent --add-service=http
    firewall-cmd --reload

    b) On Debian 8:

    iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
    iptables -A INPUT -p tcp --dport 80 -j ACCEPT
    iptables -A INPUT -p tcp --dport 22 -j ACCEPT
    iptables -A INPUT -p icmp --icmp-type echo-request -j ACCEPT
    iptables -P INPUT DROP
    iptables -P OUTPUT ACCEPT
    iptables -P FORWARD DROP
    touch /etc/iptables
    iptables-save > /etc/iptables

    c) On Ubuntu 16.04:

    ufw allow OpenSSH
    ufw allow 80
    ufw default deny
    ufw enable    

    Point your web browser to:"><script>alert(1);</script>

    Use grep to fetch error messages as follows:

    grep error /usr/local/nginx/logs/error.log

    The output should include several error messages which are similar to:

    2017/02/15 14:07:54 [error] 10776#0: [client] ModSecurity: Warning. detected XSS using libinjection. [file "/usr/local/nginx/conf/owasp-modsecurity-crs/rules/REQUEST-941-APPLICATION-ATTACK-XSS.conf"] [line "56"] [id "941100"] [rev "2"] [msg "XSS Attack Detected via libinjection"] [data "Matched Data:  found within ARGS:param: x22><script>alert(1);</script>"] [severity "CRITICAL"] [ver "OWASP_CRS/3.0.0"] [maturity "1"] [accuracy "9"] [tag "application-multi"] [tag "language-multi"] [tag "platform-multi"] [tag "attack-xss"] [tag "OWASP_CRS/WEB_ATTACK/XSS"] [tag "WASCTC/WASC-8"] [tag "WASCTC/WASC-22"] [tag "OWASP_TOP_10/A3"] [tag "OWASP_AppSensor/IE1"] [tag "CAPEC-242"] [hostname ""] [uri "/index.html"] [unique_id "ATAcAcAkucAchGAcPLAcAcAY"]

    That’s it. As you see, The ModSecurity module has successfully logged this attack in accordance with its default action policy. If you want to make more custom settings, please carefully review and edit /usr/local/nginx/conf/modsecurity.conf and /usr/local/nginx/conf/owasp-modsecurity-crs/crs-setup.conf files.

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