This is a text-only version of the following page on https://raymii.org: --- Title : Configserver Firewall and Security (CSF and LFD) Author : Remy van Elst Date : 12-10-2014 URL : https://raymii.org/s/articles/Configserver_Firewall_and_Security_CSF_LFD.html Format : Markdown/HTML --- This page covers my notes about csf and lfd. csf is an easy SPI iptables firewall suite. lfd is the login failure daemon, which scans log files for failed authentication and blocks the IP's doing that. This page covers installation, populair command line options and popular config file options.

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### CSF Installation On CentOS systems, first install some required Perl packages: yum -y install perl-libwww-perl.noarch perl-Time-HiRes Download CSF: wget http://www.configserver.com/free/csf.tgz Extract it: tar -xf csf.tgz Start the installation: cd csf ./install.sh If you have a server with Directadmin: cd csf ./install.directadmin.sh Set some sane defaults: perl -pi -w -e "s/TESTING = \"1\"/TESTING = \"0\"/" /etc/csf/csf.conf perl -pi -w -e "s/SMTP_BLOCK = \"0\"/SMTP_BLOCK = \"1\"/" /etc/csf/csf.conf perl -pi -w -e "s/LF_DSHIELD = \"0\"/LF_DSHIELD = \"86400\"/" /etc/csf/csf.conf perl -pi -w -e "s/LF_SPAMHAUS = \"0\"/LF_SPAMHAUS = \"86400\"/" /etc/csf/csf.conf perl -pi -w -e "s/LF_DIRWATCH = \"300\"/LF_DIRWATCH = \"120\"/" /etc/csf/csf.conf perl -pi -w -e "s/LF_DIRWATCH_DISABLE = \"0\"/LF_DIRWATCH_DISABLE = \"1\"/" /etc/csf/csf.conf perl -pi -w -e "s/PT_SKIP_HTTP = \"0\"/PT_SKIP_HTTP = \"1\"/" /etc/csf/csf.conf perl -pi -w -e "s/PT_USERPROC = \"10\"/PT_USERPROC = \"15\"/" /etc/csf/csf.conf perl -pi -w -e "s/CC_DENY = \"\"/CC_DENY = \"CN,KR,HK,IN,ID,MY,NG,PK,RU,SA,TW,SY,AE\"/" /etc/csf/csf.conf perl -pi -w -e "s/IGNORE_ALLOW = \"0\"/IGNORE_ALLOW = \"1\"/" /etc/csf/csf.conf Restart CSF: csf -r Done. Do note that the IP you installed from has been added to the allow list. ### csf principle The idea with csf, as with most iptables firewall configurations, is to block everything and then allow through only those connections that you want. This is done in iptables by DROPPING all connections in and out of the server on all protocols. Then allow traffic in and out from existing connections. Then open ports up in and outgoing for both TCP and UDP individually. ### csf command line tips #### Block an IP from the server csf -d 192.168.1.2 csf -d 192.168.0/24 #### Remove an IP from the blocklist csf -dr 192.168.1.2 #### Allow an IP csf -a 172.16.20.1 Do note that when you allow an IP, it will still be blocked by lfd if it starts brute forcing. See below, "Don't block IP addresses from the allow list with lfd" to see how to disable it. #### Search for an IP: csf -g 192.168.1.2 #### View Ports listening for external connections and the executables running behind them csf -p #### Disable csf and lfd csf -x #### Enable csf and lfd csf -e #### Restart csf csf -r #### Mail yourself a general security check of the server csf -m user@example.com #### Advanced filters These can be placed in either csf.allow or csf.deny. Allow connections over port 443 to a range of IP addresses: tcp|out|d=443|d=12.34.56.78/27 # csf.allow Allow SSH from one IP: tcp|in|d=22|s=23.45.67.88 # csf.allow Block traffic to port 80 from a specific range: tcp|out|d=80|d=12.34.56.78/24 #csf.deny The syntax for the advanced rules: tcp/udp|in/out|s/d=port|s/d=ip|u=uid tcp/udp : EITHER tcp OR udp OR icmp protocol in/out : EITHER incoming OR outgoing connections s/d=port : EITHER source OR destination port number (or ICMP type) (use a _ for a port range, e.g. 2000_3000) s/d=ip : EITHER source OR destination IP address u/g=UID : EITHER UID or GID of source packet, implies outgoing connections, s/d=IP value is ignored ### csf.conf highlights The `/etc/csf/csf/csf.conf` file is huge and I recommend you read through it. Below I'll highlight some parts of the config I use more often. #### Don't block IP addresses from the allow list with lfd By default `lfd` will also block IP addresses listed in the `csf.allow` file. Change the following to make `lfd` ignore IP addresses on that list. IGNORE_ALLOW = "1" Do note that if one of those IP's starts brute forcing the server, they will not be blocked. #### Open/Allow ports To allow incoming connections to a specific port, edit the following part of the config: # Allow incoming TCP ports TCP_IN = "20,21,22,25,53,80,110,143,443,465,587,993,995,2222" # Allow incoming UDP ports UDP_IN = "20,21,53" To allow outgoing ports: # Allow outgoing TCP ports TCP_OUT = "20,21,22,25,53,80,110,113,443,2222" # Allow outgoing UDP ports # To allow outgoing traceroute add 33434:33523 to this list UDP_OUT = "20,21,53,113,123" #### Allow incoming / outgoing ping / ICMP To allow ICMP/ping, in/out, change the following: # Allow incoming PING ICMP_IN = "1" # Allow outgoing PING ICMP_OUT = "1" To block it, change it to "0" #### Block certain country's To block all traffic coming from certain country's: CC_DENY = "CN,KR,HK,IN,ID,MY,NG,PK,RU,SA,TW,SY,AE" Use the 2 letter ISO code there. #### Disable tracking of long running processes PT_LIMIT = "0" If that is set to 1 you will receive a lot of mails when process resource usage spikes or they run longer than a minute. #### Enable a Web Management UI To enable the CSF web management UI, without having a controlpanel (like cpanel/directadmin): UI = "0" UI_PORT = "6666" UI_USER = "username" UI_PASS = "password" #### Send an email when a user logs in via ssh LF_SSH_EMAIL_ALERT = "1" The emails are sent to `root` by default. Change the below line to change that: LF_ALERT_TO = "user@example.org" [1]: https://www.digitalocean.com/?refcode=7435ae6b8212 --- License: All the text on this website is free as in freedom unless stated otherwise. This means you can use it in any way you want, you can copy it, change it the way you like and republish it, as long as you release the (modified) content under the same license to give others the same freedoms you've got and place my name and a link to this site with the article as source. This site uses Google Analytics for statistics and Google Adwords for advertisements. You are tracked and Google knows everything about you. Use an adblocker like ublock-origin if you don't want it. 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