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Table of Contents

Try Ubuntu now

Try Ubuntu World ===> https://github.com/charlietag/ubuntu_security

Purpose

This presumes that you've done with os_preparation

  1. This is used for check if your linux server is being hacked.
  2. This could also help you to enhance your servers' security with firewalld and fail2ban.
  3. This is also designed for PRODUCTION single server, which means this is suit for small business.

Supported Environment

  • CentOS Stream release 9

    • os_preparation
      • release : master v3.x.x

  • CentOS Stream release 8

    • os_preparation
      • release : v2.x.x

  • CentOS 8 (8.x)

    • os_preparation
      • release : v1.x.x

  • CentOS 7 (7.x) (deprecated)

    • os_preparation
      • release : v0.x.x

Warning

  • If you found something is weired and not sure if you've been hacked. You'd better reinstall your server.
  • ClamAV (clamscan) - if you're going to scan virus through clamscan (ClamAV), which is installed by default (os_security)
    • clamscan is a memory monster
    • RAM (Physical + SWAP) Capacity recommendations for clamscan (ClamAV): >= 4GB
    • (Tip) mkswap if RAM is insufficient to run clamscan
  • If your physical memory is <= 1GB, be sure stop some service before getting started

    • (Nginx) is needed when TLS (certbot) certificates is required

      echo "mariadb php-fpm puma" | sed 's/ /\n/g' | xargs -I{} bash -c "echo --- Stop / Disable {} ---; systemctl stop {} ; systemctl disable {}; echo"

    • Nginx is not needed, when NO TLS certificates required

      echo "mariadb php-fpm puma nginx" | sed 's/ /\n/g' | xargs -I{} bash -c "echo --- Stop / Disable {} ---; systemctl stop {} ; systemctl disable {}; echo"

Quick Install

Configuration

  • Download and run check

    dnf install -y git
git clone https://github.com/charlietag/os_security.git

  • Make sure config files exists , you can copy from sample to modify.

    cd databag
ls |xargs -I{} bash -c "cp {} \$(echo {}|sed 's/\.sample//g')"

  • Mostly used configuration :

    • DEV use (server in Local)

      • NO NEED to setup config, just ./start -a without config, by default, the following will be executed

        functions/
├── F_00_list_os_users
├── F_01_CHECK_01_os
├── F_01_CHECK_02_failed_login
├── F_01_CHECK_03_last_login
├── F_01_CHECK_04_ssh_config
├── F_02_PKG_02_install_perf_tools
├── F_02_PKG_04_firewalld_01_install
├── F_02_PKG_05_fail2ban_01_install

    • DEV use (server in Cloud)

      • It would be better to work with VPS Firewall for more secure enviroment
        • Firewalld + Fail2ban + VPS Firewall (Vultr / DigitalOcean)
      databag/
├── F_02_PKG_01_install_log_analyzer.cfg
├── F_02_PKG_04_firewalld_02_setup.cfg (rementer add customized port for dev, like 8000 for laravel, 3000 for rails)
├── F_02_PKG_05_fail2ban_02_setup.cfg
├── F_02_PKG_05_fail2ban_03_nginx_check_banned.cfg
├── F_02_PKG_07_nginx_01_ssl_enhanced.cfg
├── F_02_PKG_08_redmine_01_fail2ban.cfg
├── F_03_CHECK_01_check_scripts.cfg
└── _postfix.cfg
      • F_02_PKG_21_install_clamav.cfg
      • _nginx_modules.cfg

    • Production use (server in Local)

      databag/
├── F_02_PKG_01_install_log_analyzer.cfg
└── _postfix.cfg
      • F_02_PKG_21_install_clamav.cfg

    • Production use (server in Cloud)

      databag/
├── _certbot.cfg
├── F_02_PKG_01_install_log_analyzer.cfg
├── F_02_PKG_04_firewalld_02_setup.cfg
├── F_02_PKG_05_fail2ban_02_setup.cfg
├── F_02_PKG_05_fail2ban_03_nginx_check_banned.cfg
├── F_02_PKG_07_nginx_01_ssl_enhanced.cfg
├── F_02_PKG_07_nginx_02_ssl_site_config.cfg
├── F_02_PKG_08_redmine_01_fail2ban.cfg
├── F_03_CHECK_01_check_scripts.cfg
└── _postfix.cfg
      • F_02_PKG_21_install_clamav.cfg
      • _nginx_modules.cfg

  • Verify config files (with syntax color).

    cd databag

echo ; \
ls *.cfg | xargs -I{} bash -c " \
echo -e '\e[0;33m'; \
echo ---------------------------; \
echo {}; \
echo ---------------------------; \
echo -n -e '\033[00m' ; \
echo -n -e '\e[0;32m'; \
cat {} | grep -vE '^\s*#' |sed '/^\s*$/d'; \
echo -e '\033[00m' ; \
echo "

  • Verify ONLY modified config files (with syntax color).

    cd databag

echo ; \
ls *.cfg | xargs -I{} bash -c " \
echo -e '\e[0;33m'; \
echo ---------------------------; \
echo {}; \
echo ---------------------------; \
echo -n -e '\033[00m' ; \
echo -n -e '\e[0;32m'; \
cat {} | grep -v 'plugin_load_databag.sh' | grep -vE '^\s*#' |sed '/^\s*$/d'; \
echo -e '\033[00m' ; \
echo "

Installation

  • First time finish os_preparation, be sure to do a REBOOT, before installing os_security

  • Run ALL to do the following with one command

    • ./start -a
    • Run security check
    • Install security package "firewalld" , "fail2ban" , "letsencrypt" , "nginx waf" , "nginx header"

  • To avoid running ALL, to APPLY and DESTROY letsencrypt cert at the same time.

    • DO NOT run ./start.sh -a

Run Security Check

Basic os check

  • Command

    ./start.sh -i \
  F_00_debug \
  F_00_list_os_users \
  F_01_CHECK_01_os \
  F_01_CHECK_02_failed_login \
  F_01_CHECK_03_last_login \
  F_01_CHECK_04_ssh_config \
  F_01_CHECK_05_hosts_config \
  ...

  • Check OS

    • Verify os basic command (ls,cp, etc..) using command "rpm -Vf"

  • Check failed loging

    • Check failed attempt ssh login

  • Check ssh config

    • Check if root permit
    • Check if ssh port set to default 22

  • List os users

    • Check current how many common user created

  • Check last login

    • Check latest successfully login

  • Check hosts file (/etc/hosts)

    127.0.0.1 original content
::1       original content
127.0.0.1 $(hostname)
::1       $(hostname)

Installed Packages

  • Firewalld
    • Allowed port
      • http
      • https
      • 2222
  • Fail2ban
    • Default filtered
      • sshd (mode=aggressive)
      • nginx-limit-req
      • nginx-botsearch

Quick Note - Package

Nginx module - os_preparation

  • limit_req_zone
    • This is installed by default on my os_preparation repo
    • This would prevent your server from DDOS attacks.

NGINX 3rd Party Modules - os_security

https://www.nginx.com/resources/wiki/modules/

  • Headers More

    more_set_headers    "Server: CharlieTag"; # Default=> Nginx: "nginx" , Apache: "Apache"

  • ModSecurity

    ...
modsecurity on;
...

  • ModSecurity - supported policies

    • OWASP CRS

      • https://github.com/SpiderLabs/owasp-modsecurity-crs
      • Memory consumption
        • 100 MB / per nginx process
      • Should reference Azure config, to Avoid False Positive
      • Reference: REQUEST-900-EXCLUSION-RULES-BEFORE-CRS.conf.example , RESPONSE-999-EXCLUSION-RULES-AFTER-CRS.conf.example

        • REQUEST-900-EXCLUSION-RULES-BEFORE-CRS.conf.example

          • Usage

            # ModSecurity Rule Exclusion: Disable all SQLi and XSS rules
SecRule REQUEST_FILENAME "@beginsWith /admin" \
    "id:1004,\
    phase:2,\
    pass,\
    nolog,\
    ctl:ruleRemoveById=941000-942999"
# This would cause error
# ...no SecRule specified...
# ctl:ruleRemoveById=941000-942999"

        • RESPONSE-999-EXCLUSION-RULES-AFTER-CRS.conf.example

          • Usage

            SecRuleRemoveById 949100 949110 959100

    • COMODO

      • https://waf.comodo.com
      • Memory consumption
        • 300 MB / per nginx process
      • Recommended: COMODO (register an account for 1-year-free, require renew 1-year-free order every year)
      • OWSASP would have false positive while:
        • Wordpress , updating articles
        • Redmine , Click between pages

    • Website Vulnerability Scanner

      • nikto

        • Install

          dnf install -y nikto

        • Start to scan

          nikto -h myrails.centos8.localdomain

      • skipfish

        • Install

          dnf install -y skipfish

        • Start to scan (output_result_folder must be an empty folder)

          skipfish -o output_result_folder http://myrails.centos8.localdomain

Firewalld usage

- Default block all traffic, except rules you define below

  • Allow/revoke specific service

    firewall-cmd --add-service=http --permanent
firewall-cmd --remore-service=http --permanent

  • Allow/revoke specific port

    firewall-cmd --add-port=2222/tcp --permanent
firewall-cmd --remove-port=2222/tcp --permanent

  • List all current rules setting

    firewall-cmd --list-all

  • After setup done with argument "--permanent", all rules save into the following file by default

    /etc/firewalld/zone/public.xml

  • So reload firewalld to activate setting.

    firewall-cmd --reload

  • Services(http,https) defines in

    /usr/lib/firewalld/services/*

  • After running this installation, your firewalld will only allow http , https , customized ssh port

Fail2ban usage

- Setting: port, in fail2ban configuration is based on firewalld services name.

- Determine if rules of fail2ban is inserted into nft via firewalld command

  • Confirm fail2ban works with nft well

    nft list ruleset | grep {banned_ip}

  • List fail2ban status

    fail2ban-client status

  • List detailed status for specific JAIL NAME, including banned IP

    fail2ban-client status nginx-botsearch

  • Unban banned ip for specific JAIL NAME

    fail2ban-client set nginx-botsearch unbanip 192.168.1.72

  • Unban banned specific ip for all JAIL NAME

    fail2ban-client unban 192.168.1.72 ... 192.168.1.72

  • List banned ip timeout for specific JAIL NAME

    ipset list fail2ban-nginx-botsearch

  • Fail2ban keeps showing WARN

    2019-12-11 16:23:53,108 fail2ban.ipdns          [4812]: WARNING Unable to find a corresponding IP address for xxx.xxx.xxx.xxx.server.com: [Errno -5] No address associated with hostname

    • Solution

      • fail2ban-client unban --all
      • fail2ban-client restart

    • Root cause (Not verified)

      • fail2ban will dns lookup / dns reserve lookup hostname, this will trigger this error message
      • fail2ban will not dns lookup / dns reserve lookup 127.0.0.1
      • And why VM test server will not show this err message
        • The hostname of VM test server is not in /etc/hosts but also not in dns. So all the results when dns resolves. are NXDOMAIN, the same result... PASS

    • Solution 1

      • make sure hostname is in /etc/hosts (both ipv4 and ipv6 is needed)

        # cat /etc/hosts
127.0.0.1 web.example.com
::1       web.example.com

    • Solution 2

      • make sure DNS record is correct
        • A record
          • web.example.com A xxx.xxx.xxx.xxx
        • PTR record (reverse record)
          • xxx.xxx.xxx.xxx PTR web.example.com

Quick Note - Fail2ban flow

  • (Procedure) Be sure to start "Firewalld / Fail2ban" in the following order

    systemctl stop fail2ban
systemctl stop firewalld
systemctl start firewalld
systemctl start fail2ban
  • The following flow are executed automatically by Fail2ban

    • Create [ipset-nmae] (What actually done behind)

      ipset create <ipmset> hash:ip timeout <bantime>

    • Reject all traffic with [ipset-name] (What actually done behind)

      firewall-cmd --direct --add-rule <family> filter <chain> 0 -p <protocol> -m multiport --dports <port> -m set --match-set <ipmset> src -j <blocktype>

    • Parse log

    • Found illigal IP

    • Ban IP using ipset with timeout argument (What actually done behind)

      ipset add <ipmset> <ip> timeout <bantime> -exist

Quick Note - Fail2ban all detailed status

  • List all jail detailed status in faster way

    Command

    # fail2ban-client status|tail -n 1 | cut -d':' -f2 | sed "s/\s//g" | tr ',' '\n' |xargs -I{} bash -c "echo \"----{}----\" ;fail2ban-client status {} ; echo "

    Result

    ----nginx-botsearch----
Status for the jail: nginx-botsearch
|- Filter
|  |- Currently failed: 0
|  |- Total failed:     0
|  `- File list:        /var/log/nginx/error.log /var/log/nginx/default.error.log /var/log/nginx/redmine.centos8.localdomain.error.log /var/log/nginx/myrails.centos8.localdomain.error.log /var/log/nginx/mylaravel.centos8.localdomain.error.log
`- Actions
   |- Currently banned: 1
   |- Total banned:     1
   `- Banned IP list:   10.255.255.254

----nginx-limit-req----
Status for the jail: nginx-limit-req
|- Filter
|  |- Currently failed: 0
|  |- Total failed:     0
|  `- File list:        /var/log/nginx/error.log /var/log/nginx/default.error.log /var/log/nginx/redmine.centos8.localdomain.error.log /var/log/nginx/myrails.centos8.localdomain.error.log /var/log/nginx/mylaravel.centos8.localdomain.error.log
`- Actions
   |- Currently banned: 1
   |- Total banned:     1
   `- Banned IP list:   10.255.255.254

----nginx-modsecurity----
Status for the jail: nginx-modsecurity
|- Filter
|  |- Currently failed: 0
|  |- Total failed:     1
|  `- File list:        /var/log/nginx/error.log /var/log/nginx/default.error.log /var/log/nginx/redmine.centos8.localdomain.error.log /var/log/nginx/myrails.centos8.localdomain.error.log /var/log/nginx/mylaravel.centos8.localdomain.error.log
`- Actions
   |- Currently banned: 1
   |- Total banned:     1
   `- Banned IP list:   10.255.255.254

----nginx-redmine----
Status for the jail: nginx-redmine
|- Filter
|  |- Currently failed: 0
|  |- Total failed:     0
|  `- File list:        /home/rubyuser/rails_sites/redmine/log/production.log
`- Actions
   |- Currently banned: 1
   |- Total banned:     1
   `- Banned IP list:   10.255.255.254

----sshd----
Status for the jail: sshd
|- Filter
|  |- Currently failed: 0
|  |- Total failed:     0
|  `- Journal matches:  _SYSTEMD_UNIT=sshd.service + _COMM=sshd
`- Actions
   |- Currently banned: 1
   |- Total banned:     1
   `- Banned IP list:   10.255.255.254

Install SSL (Letsencrypt) - A+

Setup Nginx

This will automatically setup after installation

Also you will get a score "A+" in SSLTEST

Default : TLS 1.2 1.3 enabled

Certbot prerequisite

You will need 2 privileges

  1. Web server control , to install ssl certificates.
  2. DNS control , to do ACME verification using TXT record.

Certbot usage

  • Sign certificate (RECOMMEND), verified by DNS txt record

    certbot-auto --agree-tos -m $certbot_email --no-eff-email certonly --manual --preferred-challenges dns -d {domain}

  • Sign certificate , verified by web server root

    certbot-auto --agree-tos -m $certbot_email --no-eff-email certonly --webroot -w /{PATH}/laravel/public -d {domain} -n

  • Display all certificates

    certbot-auto certificates

  • Renew all certificates

    certbot-auto renew

  • Revoke and delete certificate

    certbot-auto revoke --cert-path /etc/letsencrypt/live/{domain}/cert.pem
certbot-auto delete --cert-name {domain}

  • New site - url : gen nginx site config + apply letsencrypt ssl only

    ./start.sh -i F_02_PKG_06_nginx_02_ssl_site_config

    Before going on, be sure http port is reachable, otherwise webroot will fail (limitation for webroot verification!)

    ./start.sh -i F_02_PKG_07_certbot_02_apply_webroot

  • New site - url (wildcard) : gen nginx site config + apply letsencrypt ssl only

    ./start.sh -i F_02_PKG_06_nginx_02_ssl_site_config
./start.sh -i F_02_PKG_07_certbot_02_apply_dns-cloudflare

Log analyzer

GoAccess usage

- Generate nginx http log report in html.

Reference the official description GoAccess

cat xxx.access.log | goaccess > xxx.html

Logwatch usage

- View log analysis report.

logwatch

pflogsumm usage (not installed by default, use logwatch instead)

- View log analysis of postfix.

/usr/sbin/pflogsumm -d yesterday /var/log/maillog

Performance monitor

Glances usage (not installed by default, not provide by CentOS 8 - base,epel,appstream)

- Just like command "top", but more than that.

glances

Iotop usage

- Just like command "top", but just for IO.

iotop

CHANGELOG

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Check if linux server is hacked, and enhance your CentOS server

Topics

nginx waf firewalld fail2ban modsecurity-nginx centos8 ssl-letsencrypt

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