This is a text-only version of the following page on https://raymii.org:
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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
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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 [email protected]


#### 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 = "[email protected]"


  [1]: https://www.digitalocean.com/?refcode=7435ae6b8212

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