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 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"
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