hardening centos

Configure user account. logout and relogin as user. su wherever required.
useradd
eg. useradd myodduser

passwd myodduser

Configure Default runlevel to runlevel 3
Use your favorite text editor to edit /etc/inittab
Find a line that is similar to the following:
id:3:initdefault:

Verify the no. after “id:” id-colon is 3. If it is not make it three.

To restrict virtual terminals to two:
Find out following stanza to enable only two virtual terminals available:

# Run gettys in standard runlevels
1:2345:respawn:/sbin/mingetty tty1
2:2345:respawn:/sbin/mingetty tty2
3:2345:respawn:/sbin/mingetty tty3
4:2345:respawn:/sbin/mingetty tty4
5:2345:respawn:/sbin/mingetty tty5
6:2345:respawn:/sbin/mingetty tty6

Make it to:

# Run gettys in standard runlevels
1:2345:respawn:/sbin/mingetty tty1
2:2345:respawn:/sbin/mingetty tty2
#3:2345:respawn:/sbin/mingetty tty3
#4:2345:respawn:/sbin/mingetty tty4
#5:2345:respawn:/sbin/mingetty tty5
#6:2345:respawn:/sbin/mingetty tty6

Save /etc/inittab and exit

Edit /etc/fstab . For the file systems /tmp, /var, and /home replace the "defaults" with "noexec,nodev,nosuid"

noexec : Binaries are not allowed to be executed. NEVER use this option for your root file system!
nosuid : Blocks the operation of suid, and sgid bits.
nodev : Prevent any user to mount the file system.


Disable unused services in order to save on resources and minimize potential security holes.
These Services that are to be stopped are mentioned here, check appendix A in case of custom requirements.


NetworkManager
NetworkManagerDispatacpid
apmd
autofs
avahi-daemon
avahi-dnsconfd
bluetooth
conman
cpuspeed
cups
dc_client
dc_server
dhcdbd
dund
firstboot
gpm
haldaemon
hidd
ibmasm
ip6tables
ipmi
irda
irqbalance
kdump
kudzu
mcstrans
mdmonitor
mdmpd
microcode_ctl
netfs
netplugd
nfs
nfslock
nscd
oddjobd
pand
pcscd
portmap
rdisc
restorecond
rpcgssd
rpcidmapd
rpcsvcgssd
saslauthd
setroubleshoot
smartd
smb
squid
tux
winbind
wpa_supplicant
xfs
ypbind
yum-updatesd



With following command format:

chkconfig –level 12345 off

To stop if any of the service is running:
service stop

check /etc/hosts
It must be in the format. (See the 127.0.0.1 line)
127.0.0.1 localhost.localdomain localhost
IP.AD.DR.ESS machine.domain.name machine



Edit /etc/host.conf
order bind,hosts
multi on
nospoof on


Edit /etc/sysctl.conf - tighten
1. net.ipv4.tcp_syncookies = 1 # Enable TCP SYN Cookie Protection
2. net.ipv4.conf.all.accept_source_route = 0 # Disables IP source routing
3. net.ipv4.conf.all.accept_redirects = 0 # Disable ICMP Redirect Acceptance
4. net.ipv4.conf.all.rp_filter = 1 # Enable IP spoofing protection, turn on source route verification
5. net.ipv4.icmp_echo_ignore_broadcasts = 1 # Enable ignoring broadcasts request
6. net.ipv4.icmp_ignore_bogus_error_responses = 1 # Enable bad error message Protection
7 net.ipv4.conf.all.log_martians = 1 # Log Spoofed Packets, Source Routed Packets, Redirect Packets

Edit /etc/hosts.deny
portmap: ALL

Edit /etc/hosts.allow
portmap: localhost
portmap: 127.0.0.1

SSH:
Disable RootLogin, force protocol 2, (explore restricting SSH to users/groups )
Protocol 2
HostbasedAuthentication no
PermitRootLogin no
PermitEmptyPasswords no
UsePrivilegeSeparation yes
AllowTcpForwarding no
X11Forwarding no
StrictModes yes
AllowUsers admin user1 user2 user3 (put actual users here in place of userN)



Stripping It Down

Following rpms are to be removed (You may add or remove some packages from this list in order to satisfy your environment.)


xkeyboard-config-0.8-7.fc6
dosfstools-2.11-6.2.el5
finger-0.17-32.2.1.1
dos2unix-3.1-27.1
esound-0.2.36-3
system-config-securitylevel-1.6.29.1-1.el5
NetworkManager-0.6.4-6.el5
OpenIPMI-2.0.6-5.el5.3
apmd-3.2.2-5
acpid-1.0.4-5
system-config-network-1.3.99-1.el5
gnome-python2-gtkhtml2-2.14.2-4.fc6
gnome-python2-bonobo-2.16.0-1.fc6
xorg-x11-drv-mouse-1.1.1-1.1
system-config-display-1.0.48-2.el5
xorg-x11-server-Xorg-1.1.1-48.13.0.1.el5
xorg-x11-server-Xvfb-1.1.1-48.13.0.1.el5
gnome-mime-data-2.4.2-3.1
centos-release-notes-5.0.0-2
xorg-x11-filesystem-7.1-2.fc6
xorg-x11-xauth-1.0.1-2.1
xorg-x11-xkb-utils-1.0.2-2.1
talk-0.17-29.2.2
cpuspeed-1.2.1-1.45.el5
hicolor-icon-theme-0.9-2.1
alsa-lib-1.0.12-3.el5
GConf2-2.14.0-9.el5
xorg-x11-utils-7.1-2.fc6
bluez-gnome-0.5-5.fc6
xorg-x11-xinit-1.0.2-13.el5
ypbind-1.19-7.el5
firstboot-tui-1.4.27.2-1.el5.centos.1
system-config-soundcard-2.0.6-1.el5
yp-tools-2.9-0.1
system-config-samba-1.2.39-1.el5
system-config-kdump-1.0.9-3.el5
tux-3.2.18-9.fc6
xorg-x11-fonts-base-7.1-2.1.el5
gnome-python2-canvas-2.16.0-1.fc6
gnome-mount-0.5-3.el5
xorg-x11-drv-vesa-1.2.1-5.2.el5
xorg-x11-drv-keyboard-1.1.0-2.1
xorg-x11-drv-evdev-1.0.0.5-2.el5
samba-common-3.0.23c-2.el5.2.0.2
xorg-x11-xfs-1.0.2-4
samba-client-3.0.23c-2.el5.2.0.2
xorg-x11-server-Xnest-1.1.1-48.13.0.1.el5
samba-3.0.23c-2.el5.2.0.2
gpm-1.20.1-74.1
xorg-x11-server-utils-7.1-4.fc6
redhat-menus-6.7.8-1.el5
metacity-2.16.0-8.el5
alsa-utils-1.0.12-3.fc6
OpenIPMI-libs-2.0.6-5.el5.3
portmap-4.0-65.2.2.1
nfs-utils-1.0.9-16.el5
system-config-nfs-1.3.23-1.el5
subversion-1.4.2-2.el5
gnome-python2-gconf-2.16.0-1.fc6
gnome-python2-extras-2.14.2-4.fc6
gnome-python2-gnomevfs-2.16.0-1.fc6
xorg-x11-drv-void-1.1.0-3.1









Security and management tool installations and fine tuning:

Security Tools Download, install and run:

a. chkrootkit - http://www.chkrootkit.org/download/
Download to /usr/local/src
Extract using "tar -zxf"
Compile & Install using "make sense"
Run chkrootkit

b. rkhunter - http://www.rootkit.nl/projects/rootkit_hunter.html
Download to /usr/local/src
Extract using "tar -zxf"
Install using ./install.sh
./installer.sh --layout /usr/local –install
rkhunter --update
Run "rkhunter -c --createlogfile"



Management Tool:. Download, install, configure: Webmin with SSL

Package Dependencies
Ensure openssl and openssl-devel are installed
rpm -q openssl
rpm -q openssl-devel
If they are not installed, install them using:
yum install openssl openssl-devel -y
(Mention ONLY those packages that need to be installed).

Download the Webmin RPM - http://www.webmin.com/
Download the RPM to /usr/local/src
Install using rpm -Uvh
Go to https://IP.AD.DR.ESS:10000 to configure. Login with user root, and password
1. Under Webmin -> Users -> Edit the root user. Rename root user to "admin"
2. Under Logging ensure all events by all users are logged
3. Change the port from 10000 to a suitable one above 50000 (and below 60000).
4. Under Authntication - set the idle time-out to 5 minutes.

d. Perl Libraries

Net::SSLeay - http://www.cpan.org/modules/by-module/Net/Net_SSLeay.pm-1.30.tar.gz
Download to /usr/local/src/
Extract with tar -xzf
Prepare with "perl Makefile.PL"
Compile & Install with "make install"
Test installation with "perl -e 'use Net::SSLeay'". You should be returned to the prompt. If you get errors, the installation did not succeed.



e. Portsentry -ftp://194.199.20.114/linux/freshrpms/fedora/linux/1/portsentry/portsentry-1.1-11.fr.i386.rpm
Download the RPM to /usr/local/src
Install using rpm -Uvh
Edit /etc/portsentry/portsentry.conf
Edit /etc/portsentry/portsentry.modes
Edit /etc/portsentry/portsentry.ignore
Start portsentry.

f. Checksuite - http://checksuite.sourceforge.net/
Download the RPM to /usr/local/src
Install using rpm -Uvh


g. Fine Tuning IPTABLES:
edit /etc/sysconfig/iptables

Insert rules for trusted ip addresses only which should access ssh port.

-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -s -j ACCEPT

These rules are to be added before following rule:
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited