Few Securing a LInux server tips

#Reference:http://www.cisecurity.org/bench_linux.html

#Note:This tutorial is based on Fedora Core 4.Should be valid for a newer version of Fedora too.The reader is advised to read the CIS Benchmark pdf after completing all activities mentioned in this document.

# Setup an informative command prompt
export PS1="-\$?-(\u@\h) \w > "


# Hostname Setup
Reference:http://www.cpqlinux.com/hostname.html

# Please ensure that the correct hostname is setup in the following files.The hostname should ideally match the PTR record of the system IP
/etc/hosts
/etc/sysconfig/network
# Use echo to set the hostname in the file below eg.
echo yourhostname > /proc/sys/kernel/hostname
/proc/sys/kernel/hostname
# Virtual IP Setup
cd /etc/sysconfig/network-scripts

#Check for existing network adapters with the command:

ls ifcfg-*

#In most instances, you will see the files ifcfg-eth0 and ifcfg-lo. If you see other files with any other names and are unfamiliar with configuring TCP/IP, you may want to consult with your system administrator before proceeding.

cp -a ifcfg-eth0 ifcfg-eth0:0
cp -a ifcfg-eth0 ifcfg-eth0:1
# Ensure the following lines are configured as

vi icfg-eth0:0
DEVICE=eth0:0
IPADDR=
VLAN=yes

vi icfg-eth0:1
DEVICE=eth0:1
IPADDR=
VLAN=yes

#Disable IPV6

cp -a /etc/modprobe.conf /etc/modprobe_backup.conf
echo "alias net-pf-10 off" >> /etc/modprobe.conf
echo "alias ipv6 off" >> /etc/modprobe.conf

/etc/init.d/ip6tables stop
/sbin/chkconfig --level 35 ip6tables off

# Restart the network to effect changes

/sbin/service network restart

# Edit /etc/hosts and add a line for your new addresses and name such as:
127.0.0.1 localhost.localdomain localhost
x.x.x.x newhost1.yourdomain.com
x.x.x.x newhost2.yourdomain.com


# Disabling selinux

vi /etc/sysconfig/selinux
#check for the line SELINUX
SELINUX=disabled

# Date and Time Configuration

Ref:http://www.linuxsa.org.au/tips/time.html

ln -sf /usr/share/zoneinfo/Asia/Calcutta /etc/localtime

date monthdayhourminyear

yum install ntp

#Configure a cron job to update time every night at 12 AM
00 00 * * * /usr/sbin/ntpdate 0.pool.ntp.org 1.pool.ntp.org

# Configure Automatic Updates using yum.Fedora Core 6 or above will have yum-updatesd instead of yum

/sbin/chkconfig yum on
/sbin/service yum start

# If you wish to disable autoupdation of some package, eg.firefox and cacti ,do the following
cp -a /etc/yum.conf /etc/yum.conf.orig
vi /etc/yum.conf
# Add the following line
exclude=firefox cacti

# For Fedora Core 6 or above do this
# Reference: http://www.die.net/doc/linux/man/man5/yum-updatesd.conf.5.html
cp -a /etc/updatedb.conf /etc/updatedb.conf.orig
vi /etc/yum/yum-updatesd.conf

#########
# Configure the entries as shown below
# automatically install updates
do_update = yes
# automatically download updates
do_download = yes
# automatically download deps of updates
do_download_deps = yes
#########

/sbin/chkconfig yum-updatesd on
/sbin/service yum-updatesd start

crontab -e

00 0 * * * yum -y update

# Configuring updatedb
cp -a /etc/updatedb.conf /etc/updatedb.conf.orig

vi /etc/updatedb.conf
#Configure the following values to yes
#DAILY_UPDATE=no
DAILY_UPDATE=yes

# Configuring Log Compression
cp -a /etc/logrotate.conf /etc/logrotate.conf.orig
vi /etc/logrotate.conf

# uncomment this if you want your log files compressed
compress

# Unalias cp and mv

unalias mv cp

# Firewall ,Reactive IDS and SSH bruteforce prevention setup

Please install and configure shorewall ,psad and fail2ban by referring their separate howtos

# Apache Installation

# Check if Apache is already installed

rpm -qa httpd
service httpd status

# If httpd is not installed proceed with the apache installation as follows

yum install httpd
yum install httpd-devel


# Apache Hardening

Edit httpd.conf file as follows.

cd /etc/httpd/conf/

cp -a httpd.conf httpd.conf.orig

vi /etc/httpd/conf/httpd.conf

# Edit the following entry as follows

#ServerTokens OS
ServerTokens Prod

#ServerSignature On
ServerSignature Off


#Ref:http://www.slac.stanford.edu/comp/unix/apache-security.html
#http://publib.boulder.ibm.com/httpserv/ihsdiag/http_trace.html

# Disabling Indexing
# Ref: http://www.ducea.com/2006/06/26/apache-tips-tricks-disable-directory-indexes/
# In Main Server Configurations

Options -Indexes

# To disable Trace and Track Methods:

For apache version 1.3.34 (or later 1.3.x versions), or apache 2.0.55 (or later), in section 1, add the line
TraceEnable off

For older versions of apache, see below.

#Add Before Secton 3 and in each virtual host configuration section/file
# Block access: SLAC addition
RewriteEngine On
RewriteCond %{REQUEST_METHOD} ^(TRACE|TRACK)
RewriteRule .* - [F]
# End block access rule

# Disabling welcome page
cp -a /etc/httpd/conf.d/welcome.conf /etc/httpd/conf.d/welcome.conf.orig
vi /etc/httpd/conf.d/welcome.conf
# Comment all the lines in the file

# Disabling configuration by .htaccess

AllowOverride None

# Restart Apache
/etc/rc.d/init.d/httpd start

# MySQL Installation
# Check if MySQL is already installed

rpm -qa mysql
service mysqld status

# If Mysqld Daemon is not installed proceed with the MySQL installation as follows

yum install mysql-server
yum install mysql
yum install mysql-devel

#Start MySQL for the first time

mysql_install_db
/etc/rc.d/init.d/mysqld start
#Note:In case you have issues starting Mysql server for the first time and you see error messggaes saying that tmp files could not be created,please run bastille configuration again and answer N to "Q: Would you like to install TMPDIR/TMP scripts?" question reboot the system.Post reboot you can start Mysqld

/sbin/chkconfig mysqld on

#Mysql Hardening:

mysql
# Removing anonymous login:

DELETE FROM mysql.user WHERE User = '';
FLUSH PRIVILEGES;
quit
#Setting Mysql Root password:

/usr/bin/mysqladmin -u root password 'yourpassword'
/usr/bin/mysqladmin -u root -h password 'yourpassword'

# Delete test database

mysql
drop database test;

# Configure Mysql to not listen for external connections

cp -a /etc/my.cnf /etc/my.cnf.orig

vi /etc/my.cnf

[mysqld]
skip-networking

#Perl Installation

#check if perl is installed or not

rpm -qa perl

# If Perl is not installed proceed with the Perl installation as follows

yum install perl

# Cpan configuration

# Before running cpan ensure that gcc is installed else some modules will throw errors during compilation

rpm -qa gcc

# Install gcc if not found

yum install gcc

# Run and configure cpan

cpan

# A first time set of configuration questions will be asked

# Update cpan by running

cpan
install Bundle::CPAN
reload cpan

# Bastille Hardening


#Bastille Installation

cd /tmp

wget http://nchc.dl.sourceforge.net/sourceforge/bastille-linux/Bastille-3.2.1-0.1.noarch.rpm


# Ref: http://www.bastille-linux.org/running_bastille_on.htm#top

rpm -ivh Bastille-3.2.1-0.1.noarch.rpm

# Install Curses from cpan
# Please check wheather ncurses-devel is installed

rpm -qa ncurses-devel

# If ncurses is not installed install it as follows

yum install ncurses-devel

# Install Curses module as follows

cpan

install Curses

# Run bastille text mode hardening as follows

/usr/sbin/bastille -c

# Respond to all questions

# Check your score

/usr/sbin/bastille --report


# ICMP Hardening


# Check and Download sysctl RPM
yum install sysctl

# Enter the following in /etc/sysctl.conf file
net.ipv4.icmp_echo_ignore_all = 1

net.ipv4.icmp_echo_ignore_broadcasts = 1

net.ipv4.icmp_ignore_bogus_error_responses = 1

net.ipv4.conf.all.accept_source_route = 0

net.ipv4.conf.all.accept_redirects = 0

net.ipv4.tcp_max_syn_backlog = 4096

net.ipv4.tcp_syncookies=1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.default.secure_redirects = 0
net.ipv4.tcp_max_orphans = 256
net.ipv4.conf.all.log_martians = 1

# Diable Forwarding and Gateway functionality
net.ipv4.ip_forward = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0


#Check for the syntax in the file /etc/sysctl.conf
/sbin/sysctl -p

OR
/sbin/iptables -A INPUT -j REJECT -p icmp --icmp-type 13
/sbin/iptables -A OUTPUT -j REJECT -p icmp --icmp-type 14

# Detailed audit trail setup

Ref: http://www.cyberciti.biz/tips/howto-log-user-activity-using-process-accounting.html

yum install psacct
chkconfig psacct on
/etc/init.d/psacct start

# Rootkit Hunter

Reference:http://www.rootkit.nl/

Installation:

# Download rkhunter from http://www.rootkit.nl/projects/rootkit_hunter.html
cd /tmp
wget http://nchc.dl.sourceforge.net/sourceforge/rkhunter/rkhunter-1.3.2.tar.gz
tar zxvf rkhunter-1.3.2.tar.gz
cd rkhunter-1.3.2
sh installer.sh --layout default --install

# Running Rkhunter
/usr/local/bin/rkhunter --update
/usr/local/bin/rkhunter -c --createlogfile --quiet
The report will be generated at /var/log/rkhunter.log

#Configure rkhunter for automatic update
crontab -e
00 0 * * * /usr/local/bin/rkhunter --update -q

# SSHD Hardening
cp -a /etc/ssh/sshd_config /etc/ssh/sshd_config.orig

vi /etc/ssh/sshd_config

#change port no from 22 to 222
Port 222

PermitRootLogin no

Banner /etc/issue

#This banner is generated when you ran Bastille previously.

#Prevent X11 forwarding
X11Forwarding no

#Don't read the user's ~/.rhosts and ~/.shosts files uncomment IgnoreRhosts yes
IgnoreRhosts yes

# The following switch is not found in Fedora 4.Please check the switch to ensure that it exists #before making this entry

RhostsAuthentication no

RhostsRSAAuthentication no

HostbasedAuthentication no

PermitEmptyPasswords no

#Note:Before restarting ssh please create a non-root account.

Restart sshd
/etc/rc.d/init.d/sshd restart
# Nessus Setup

# Read the Nessus How to file for installing and running Nessus

# CIS benchmark security exercise

# Download the CIS benchmark locally from http://www.cisecurity.org/bench_linux.html and copy the do-backup.sh file in /root and run the same to backup all important directories and files

cd /root
chmod 755 do-backup.sh
./do-backup.sh

# Uninstalling xinetd
rpm -qa xinetd
rpm -e xinetd-versionnumber

# Incase you still want to use some services in xinetd ,please run the following comands to stop these unnnecessary services.

cd /etc/xinetd.d
for FILE in chargen chargen-udp cups-lpd cups daytime \ daytime-udp echo echo-udp eklogin ekrb5-telnet finger \ gssftp imap imaps ipop2 ipop3 krb5-telnet klogin kshell \ ktalk ntalk pop3s rexec rlogin rsh rsync servers services \ sgi_fam talk telnet tftp time time-udp vsftpd wu-ftpd do

chkconfig ${FILE} off done

# Disable GUI
sed -e 's/id:5:initdefault:/id:3:initdefault:/' \
< /etc/inittab-preCIS > /etc/inittab
chown root:root /etc/inittab
chmod 0600 /etc/inittab
diff /etc/inittab-preCIS /etc/inittab

# Disable Unneccessary services
# Please review all services listed in the following script before running.

vi disable_unwanted_services

########
for FILE in apmd avahi-daemon canna cups-config-daemon FreeWnn gpm hidd hpoj hplip innd irda isdn kdcrotate lvs mars-nwe messagebus oki4daemon privoxy rstatd rusersd rwalld rwhod wine; do
/sbin/service $FILE stop
/sbin/chkconfig $FILE off
done

for FILE in nfs nfslock autofs ypbind ypserv yppasswdd portmap smb netfs lpd tux snmpd named postgresql webmin kudzu squid cups ip6tables pcmcia bluetooth mDNSResponder; do
/sbin/service $FILE stop
/sbin/chkconfig $FILE off
done
########

chmod 755 disable_unwanted_services
./disable_unwanted_services

# Assign Proper permissions to log files

chmod o-rwx boot.log* cron* dmesg ksyms* httpd/* maillog* messages* news/* pgsql rpmpkgs* samba/* sa/* scrollkeeper.log secure* spooler* squid/* vbox/* wtmp

chmod o-rx boot.log* cron* maillog* messages* pgsql secure* spooler* squid/* sa/*

chmod g-w boot.log* cron* dmesg httpd/* ksyms* maillog* messages* pgsql rpmpkgs* samba/* sa/* scrollkeeper.log secure* spooler*

chmod g-rx boot.log* cron* maillog* messages* pgsql secure* spooler*

chmod o-w gdm/ httpd/ news/ samba/ squid/ sa/ vbox/

chmod o-rx httpd/ samba/ squid/ sa/

chmod g-w gdm/ httpd/ news/ samba/ squid/ sa/ vbox/

chmod g-rx httpd/ samba/ sa/

chmod u-x kernel syslog loginlog

# Verify passwd, shadow, and group File Permissions

cd /etc
chown root:root passwd shadow group
chmod 644 passwd group
chmod 400 shadow

# Allowing only root access to Cron and At

cd /etc/
rm -f cron.deny at.deny
echo root > cron.allow
echo root > at.allow
chown root:root cron.allow at.allow
chmod 400 cron.allow at.allow

# Restrict Permissions On crontab Files

chown root:root /etc/crontab
chmod 400 /etc/crontab
chown -R root:root /var/spool/cron
chmod -R go-rwx /var/spool/cron
cd /etc
ls | grep cron | grep -v preCIS | xargs chown -R root:root
ls | grep cron | grep -v preCIS | xargs chmod -R go-rwx

# Block all system accounts from loging on to the server

cd /root
vi lock_system_accounts

####
cd /etc
for NAME in `cut -d: -f1 /etc/passwd`; do
MyUID=`id -u $NAME`
if [ $MyUID -lt 500 -a $NAME != 'root' ]; then
/usr/sbin/usermod -L -s /dev/null $NAME
fi
done
###

chmod 755 lock_system_accounts

./lock_system_accounts

rm -rf lock_system_accounts

# Check for empty password accounts
awk -F: '($2 == "") { print $1 }' /etc/shadow

# Set Account Expiration Parameters On Active Accounts

cd /etc
awk '($1 ~ /^PASS_MAX_DAYS/) { $2="90" }
($1 ~ /^PASS_MIN_DAYS/) { $2="7" }
($1 ~ /^PASS_WARN_AGE/) { $2="28" }
($1 ~ /^PASS_MIN_LEN/) { $2="6" }
{ print } ' login.defs-preCIS > login.defs
diff login.defs-preCIS login.defs
chown root:root login.defs
chmod 640 login.defs
diff login.defs-preCIS login.defs

useradd -D -f 7
diff /etc/default/useradd-preCIS /etc/default/useradd
for NAME in `cut -d: -f1 /etc/passwd`; do
uid=`id -u $NAME`
if [ $uid -ge 500 -a $uid != 65534 ]; then
chage -m 7 -M 90 -W 28 -I 7 $NAME
fi
done
diff shadow-preCIS shadow

# Verify No Legacy '+' Entries Exist In passwd, shadow, And group Files

grep ^+: /etc/passwd /etc/shadow /etc/group

# No '.' or Group/World-Writable Directory In Root's $PATH

#To find ‘.’ in $PATH:
echo $PATH | egrep '(^|:)(\.|:|$)'
#To find group- or world-writable directories in $PATH:
find `echo $PATH | tr ':' ' '` -type d \( -perm -002 -o -perm -020 \) -ls

#These commands should produce no output.

#User Home Directories Should Be Mode 750 or More Restrictive

vi user_directories_permission

###############
for DIR in `awk -F: '($3 >= 500) { print $6 }' /etc/passwd`; do
chmod g-w $DIR
chmod o-rwx $DIR
done
##############

chmod 755 user_directories_permission
./user_directories_permission

#No User Dot-Files Should Be World-Writable

vi user_dot_files_non_worldwritable

#############

for DIR in `awk -F: '($3 >= 500) { print $6 }' /etc/passwd`; do
for FILE in $DIR/.[A-Za-z0-9]*; do
if [ ! -h "$FILE" -a -f "$FILE" ]; then
chmod go-w "$FILE"
fi
done
done
#########

chmod 755 user_dot_files_non_worldwritable
./user_dot_files_non_worlwritable

#Remove User .netrc Files

find / -name .netrc

# If any .netrc file is found then run the following script to remove

vi remove_netrc

###############
for DIR in `cut -f6 -d: /etc/passwd`; do
if [ -e $DIR/.netrc ]; then
echo "Removing $DIR/.netrc"
rm -f $DIR/.netrc fi
done
###############

chmod 755 remove_netrc
./remove_netrc

#Set Default umask For Users

vi set_default_umask

#########
cd /etc
for FILE in profile csh.login csh.cshrc bashrc; do
if ! egrep -q 'umask.*77' $FILE ; then
echo "umask 077" >> $FILE
fi
chown root:root $FILE
chmod 444 $FILE
diff ${FILE}-preCIS $FILE
done

cd /root
for FILE in .bash_profile .bashrc .cshrc .tcshrc; do
if ! egrep -q 'umask.*77' $FILE ; then
echo "umask 077" >> $FILE # See description
fi
chown root:root $FILE
diff ${FILE}-preCIS $FILE
done
###########

chmod 755 set_default_umask
./set_default_umask


# Disable Core Dumps

cp -a /etc/security/limits.conf /etc/security/limits.conf.orig

vi /etc/security/limits.conf

#Add the following two lines.In future you can enable core dumps for invidual users if required.

* soft core 0
* hard core 0

####

# Limit Access To The Root Account From su
# Warning:Please add your account to the wheel group before proceeding with this activity else you # will not be able to su.
# eg. /usr/sbin/usermod -G wheel

# In case you want to create a new account and add it to the wheel group, then run this command
/usr/sbin/useradd -G wheel

# Limit Access To The Root Account From su

cd /etc/pam.d/
cp -a su su_backup_18_dec_2006

vi su

##Uncommenting this line allows only the users in the wheel group to become root by using the su command and entering the root password.All other users get the message Incorrect Password

auth required /lib/security/$ISA/pam_wheel.so use_uid

# Banners

# Note:/etc/issue banner should have already been created by BastilleIf you havent run Bastille please create an appropriate banner file /etc/issue as follows



***************************************************************************
NOTICE TO USERS


This computer system is the private property of , whether
individual, corporate or government. It is for authorized use only.
Users (authorized or unauthorized) have no explicit or implicit
expectation of privacy.

Any or all uses of this system and all files on this system may be
intercepted, monitored, recorded, copied, audited, inspected, and
disclosed to your employer, to authorized site, government, and law
enforcement personnel, as well as authorized officials of government
agencies, both domestic and foreign.

By using this system, the user consents to such interception, monitoring,
recording, copying, auditing, inspection, and disclosure at the
discretion of such personnel or officials. Unauthorized or improper use
of this system may result in civil and criminal penalties and
administrative or disciplinary action, as appropriate. By continuing to use
this system you indicate your awareness of and consent to these terms
and conditions of use. LOG OFF IMMEDIATELY if you do not agree to the
conditions stated in this warning.

****************************************************************************
cp -a issue.net issue_backup_todays_date.net

cp -a issue issue.net

# Contents of /etc/motd are displayed after a user logins in so its not neccessary to create a #banner in that file

chown root:root /etc/motd /etc/issue /etc/issue.net
chmod 644 /etc/motd /etc/issue /etc/issue.net

# Removing unnecessary applications
# Please refer http://www.mjmwired.net/resources/mjm-services-fc6.html for the list of services and their uses and recommendations on which to disable
cd /etc/init.d
ls

# Verify the softwares that are listed here.Remove all unnecesaasy packages as show below.

# For eg. if you see bluetooth and you want to identify what package it represnts, do the following
rpm -qf bluetooth
bluez-utils-2.15-7
yum remove bluez-utils-2.15-7

# Do this for all other softwares like portmap,apmd,cups,isdn,irda,etc.

# RHEL comes with virtualisation enabled.Due to this you may see an additional network adapter ( virbr0 ) when you run /sbin/ifconfig -a
# This can be removed by following these steps
#Source :http://www.cyberciti.biz/faq/rhel-fedora-centos-linux-remove-network-interface-virbr0/
yum groupremove "Virtualization"

# Type y when it lists the following pakcages to be removed
libvirt
libvirt-python
rhn-virtualization-host

This will also remove the virbr0 network adapter

#Firewall Configuration

/bin/netstat -ltunp

# The above command will show you list of processes running on specific ports.Please ensure that unnecassary services are disabled and uninstalled as shown in the above point.
# Open required ports in iptables using Shorewall (Please refer the separate Howto)
/usr/sbin/lokkit

# Remove All Compilers and Assemblers

#The following command will help you identify the packages installed on your system
rpm -qa | egrep "^gcc|java|bin86|dev86|nasm"

#Identify the package and remove the ones you dont need

#Verify That No Unauthorized UID 0 Accounts Exists

getent passwd | awk -F: '$3 == "0" { print $1 }'

#should return only the word "root", unless additional uid 0 accounts have been specifically authorized. Having #multiple uid 0 accounts are acceptable if the accounts are authorized, but not recommended for

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