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Initial Settings
To get started with securing your VPS or dedicated server with ConfigServer Firewall, go to the csf – ConfigServer Firewall section in the Webmin Module
Click Firewall Configuration to set all of these options
The firewall is only enabled when TESTING is set to 0, it is safe to do so since you whitelisted your IP address above using WhatIsMyIPAddress and/or Dynamic DNS
RESTRICT_SYSLOG = 0
Under Initial Settings make these changes
RESTRICT_SYSLOG = 3
Under IPv4 Port Settings
Choose TCP ports, the defaults will handle most systems but do include any additional ports from the netstat output. Remember to add port 10000 for Webmin and a custom SSH port (I’ve used 69) which you will configure later.
TCP_IN 20,21,22,25,53,80,110,143,443,465,587,993,995,69,8080,10000 TCP_OUT 20,21,22,25,53,80,110,113,443,587,993,995
Make UDP blank, generally you do not need UDP for anything on a web server unless it is streaming video or music.
UDP_IN UDP_OUT
Under IPv6 Port Settings make them match the IPv4 Port settings
TCP_IN 20,21,22,25,53,80,110,143,443,465,587,993,995,69,8080,10000 TCP_OUT 20,21,22,25,53,80,110,113,443,587,993,995
Same for UDP
UDP_IN UDP_OUT
Under General Settings
Necessary to log failed attempts, makes sure syslog service is running
SYSLOG_CHECK = 3600
SMTP Settings
Under SMTP Settings you need to know if you allow external users from remote IPs to send emails, if you only send emails using your local user set these options to block all other users except root and mailman. If you want to allow other non-local users leave SMTP_BLOCK=0 like if you are using Google’s servers as an SMTP relay to send your emails.
SMTP_BLOCK = 1 SMTP_ALLOWLOCAL = 1
To allow extra SMTP users set them in SMTP_ALLOWUSER and GROUP
SMTP_ALLOWUSER = webmaster,postmaster SMTP_ALLOWGROUP = mail
Reporting Settings
Under Reporting Settings leave the LF_ALERT_TO and LF_ALERT_FROM if you have postfix configured to autoforward to you regular email address.
Do set X_ARF to get detailed reports of intrusion alerts.
X_ARF = 1
Global Lists/DYNDNS/Blocklists
Under Global Lists/DYNDNS/Blocklists you can set custom IP lists to ignore including dynamic DNS addresses. If you set your dynamic DNS address to be ignored set these options to check the IP of the dynamic DNS address every 10 minutes and ignore the IP in the firewall rules.
DYDNS = 600 DYNDNS_IGNORE = 1
Under Country Codes Lists and Settings you can set custom countries to block. If you want to block Russia and China these country codes can be added to CC_DENY.
CC_DENY = RU,CN
Login Failure Blocking and Alerts
Under Login Failure Blocking and Alerts you can block users attempting to brute force your services like SSH, FTP, SMTP and others. The PERM setting set to 1 makes the ban permanent.
For the Login Failure daemon to permanently block failed IPs set LF_TRIGGER_PERM to 1 so it blocks that IP for all login failures which you enable in the LF_ settings that follow.
LF_TRIGGER_PERM = 1
If you are concerned about locking yourself or other friendly users out then set the LF TRIGGER to a value like 60 so that the IP is unlocked after 1 minute
LF_TRIGGER_PERM = 60
Set this option to only block users on the port they are attacking. This prevents innocent users whose machines are compromised from getting access to your services.
LF_SELECT = 1
The rest of the options are set to block the users on the specific port after a number of failed connections. You can decrease the limit for SSH from 5 to 3 like this
LF_SSHD = 3
Same goes for FTP and SMTP
LF_FTPD = 3 LF_SMTPAUTH = 3
Block Webmin failed attempts
LF_WEBMIN = 3
You can also block users requesting 404 or 403 pages from Apache – beware this can cause false positives from bots you want to crawl your site.
LF_APACHE_404 = 200 LF_APACHE_403 = 200
Under Distributed Attacks you can prevent botnets from making multiple failed attempts from different IP addresses, here the minimum amount of unique IP addresses allowed to login with the same credentials is 2
LF_DISTATTACK = 1 LF_DISTATTACK_UNIQ = 2
You should do the same with FTP, be careful with the unique IP setting if multiple users share the same account – here it is set to 3 IPs to share the same account. Make them permanent too.
LF_DISFTP = 1 LF_DISTFTP_UNIQ = 3 LF_DISTFTP_PERM = 1
Repeate the same for SMTP, again if multiple users share the same account take care with the UNIQ setting – again 3 IPs share this account.
LF_DISTSMTP = 1 LF_DISTSMTP_UNIQ = 3 LF_DISTSMTP_PERM = 1
Process Tracking
Under Process Tracking you can check rogue processes. It is usually easier to disable it by setting PT_LIMIT to disable process tracking as the amount of emails can be quite annoying. However, if you do want to use it then leave PT_LIMIT’s default value and add processes to ignore as shown for /opt/csf/pignore.
PT_LIMIT = 0
To disable any SSH attacks disconnect users who leave sessions open
PT_SSHDHUNG = 1
Note: from this point onwards no configuration is done in Webmin and is done in your SSH session.
Alternatively you can add the services to exclude from process tracking in /opt/csf/csf.pignore to stop the excessive and annoying Process Tracking Emails, this is done in SSH
nano /opt/csf/pignore
Add the services you wish to ignore there
exe:/usr/bin/dbus-daemon exe:/usr/sbin/mysqld exe:/usr/bin/nginx exe:/usr/lib/postfix/smtp exe:/usr/lib/dovecot/auth
Additional ConfigServer Firewall Setup
Use CSF Blocklists from dshield and spamhaus
sudo nano /etc/csf/csf.blocklists
Uncomment these lines by removing the hashtag # symbol, Spamhaus and Dshield block lists in CSF should not result in any false positives.
DSHIELD|86400|0|http://www.dshield.org/block.txt SPAMDROP|86400|0|http://www.spamhaus.org/drop/drop.lasso
Restart CSF
csf -r
Allowing the CloudFlare IPs should not be necessary! I use Flexible and strict SSL with CloudFlare and have not needed to do this but they do recommend it. If for some reason you need to allow the CloudFlare IPs on CSF go back in Webmin and click Firewall Allow IPs and paste this list and click Change
You can also consider adding this list to /etc/csf/csf.ignore
199.27.128.0/21; 199.27.128.0/21 173.245.48.0/20 103.21.244.0/22 103.22.200.0/22 103.31.4.0/22 141.101.64.0/18 108.162.192.0/18 190.93.240.0/20 188.114.96.0/20 197.234.240.0/22 198.41.128.0/17 162.158.0.0/15 104.16.0.0/12 172.64.0.0/13
If you set the CloudFlare allow IPs, click Return
Secure SSH for CSF
Open the SSH configuration
sudo nano /etc/ssh/sshd_config
Change the port and add UseDNS no so log files for SSH failed logins show the IP and not the domain name.
You must remember to add the port you choose here in TCP_IN for IPv4
# What ports, IPs and protocols we listen for Port 69UseDNS no
Restart SSH daemon
sudo service ssh restart
Secure MySQL
There is security risk
sudo nano /etc/mysql/my.cnf
Under [mysqld] add this
[mysqld] # # * Basic Settings # local-infile = 0 user = mysql
Restart MySQL
sudo service mysql restart
Monitor Critical System Files for Changes
ConfigServer lfd lets you monitor critical system files for changes by checking md5 sums periodically and will alert you of changes. This provides a basic Intrustion Detection System alternative to Snort, Tripwire and others.
Add the files you want to monitor here
sudo nano /etc/csf/csf.dirwatch
I have used root authorized keys and some other important files which would indicate a security breach.
CSF lfd ignores files owned by root by default but if you specify them here they will be monitored by ldf
/root/.ssh/authorized_keys /etc/ssh/sshd_config /etc/shadow
In the ConfigServer Webmin module find this setting under Directory Watching & Integrity and set it to 600 (every 10 minutes)
LF_DIRWATCH_FILE=600
Restart the CSF service in Webmin or SSH
lfd will check files ever 10 minutes for changes and send you an email alert
Time: Sat Dec 5 23:20:13 2015 +0000 File: /root/.ssh/authorized_keys has changed Output: -rw------- 1 root root 404 2015-12-05 23:19:32.727340313 +0000 /root/.ssh/authorized_keys
These CSF settings should keep you pretty safe from attacks and intrusions, my VPS is actually using less resources since activating this ConfigServer Firewall configuration