The document is a comprehensive guide on Linux server security and hardening techniques, authored by Saeid Bostandoust, an experienced software engineer and member of various tech associations. It outlines 40 essential security practices including keeping software updated, minimizing vulnerabilities, using centralized authentication services, and implementing strict user account policies. Additionally, it provides instructions on utilizing security tools and configuring systems to ensure better overall security against potential threats.

1. # whoami
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‫نویس‬ ‫برنامه‬ ‫و‬ ‫افزار‬ ‫نرم‬ ‫مهندس‬
‫سال‬ ‫از‬ ‫گنو/لینوکس‬ ‫ادمین‬ ‫سیس‬۱۳۸۵
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‫افزار‬ ‫نرم‬ ‫و‬ ‫شبکه‬ ‫امنیت‬ ‫و‬ ‫ابری‬ ‫رایانش‬ ‫و‬ ‫زیرساخت‬ ‫حوزه‬ ‫در‬ ‫فعال‬
‫های‬ ‫تکنولوژی‬ ‫و‬ ‫گنو/لینوکس‬ ‫های‬ ‫دوره‬ ‫مدرس‬Red Hat
Saeid Bostandoust
ssbostan@linuxmail.org
bostandoust.ir

2. Bostandoust.IR
# whereis `!!`
@ssbostan
.@bostandoust ir

3. Bostandoust.IR
@shirazcloud
@shirazlug

4. Bostandoust.IR
Linux Security and Hardening

5. Bostandoust.IR
#1
Keep Linux Kernel and Software Up to Date
# yum update
# yum install yum-cron

6. Bostandoust.IR
#2
Minimize Software to Minimize Vulnerabilities
Remove Unwanted Software and Services

7. Bostandoust.IR
#3
One Network Service Per System or VM Instance
Containerized Services

8. Bostandoust.IR
#4
Don’t Use Graphical Environment on Servers
Real sysadmins do not needs any graphical environments!
# yum group remove "X Window System"
# yum group remove "GNOME Desktop"
# yum group remove "Server with GUI"

9. Bostandoust.IR
#5
Use A Centralized Authentication Service
FreeIPA, OpenLDAP

10. Bostandoust.IR
#6
Use Linux Security Extensions (SELinux)
# sestatus
# vi /etc/selinux/config

11. Bostandoust.IR
#7
Linux Kernel /etc/sysctl.conf Hardening

12. Bostandoust.IR
#8
Disable Memory Core Dumps
# echo * hard core 0 >> /etc/security/limits.conf
# echo fs.suid_dumpable = 0 >> /etc/sysctl.conf

13. Bostandoust.IR
#9
Disable USB Storage / Firewire / Thunderbolt
# echo install usb-storage /bin/true >> /etc/modprobe.d/usb-storage.conf
# echo blacklist usb-storage >> /etc/modprobe.d/usb-storage.conf
# echo blacklist firewire-core >> /etc/modprobe.d/firewire.conf
# echo blacklist thunderbolt >> /etc/modprobe.d/thunderbolt.conf

14. Bostandoust.IR
#10
Find and Disable Users with Empty Passwords
# awk -F: '($2 == "") {print}' /etc/shadow
# usermod -L USER
# chage -E 0 USER

15. Bostandoust.IR
#11
Make Sure No Non-Root Accounts Have UID Set To 0
# awk -F: '($3 == "0") {print}' /etc/passwd
# userdel -frZ USER

16. Bostandoust.IR
#12
User Accounts Strong Password Policy
pam_pwquality.so
https://access.redhat.com/solutions/2808101

17. Bostandoust.IR
#13
Restricting Users from Reusing Old Passwords
pam_pwhistory.so
Don’t use pam_unix (MD5)
/etc/security/opasswd

18. Bostandoust.IR
#14
Password Aging For Better Security
# vi /etc/login.defs
# chage -d 0 USER
# chage -E 0 USER
# chage -M 30 -m 3 -W 3 USER

19. Bostandoust.IR
#15
Locking User Accounts After Login Failures
# vi /etc/pam.d/system-auth
# vi /etc/pam.d/password-auth
auth required pam_tally2.so audit deny=3 unlock_time=60 even_deny_root
account required pam_tally2.so
auth requisite pam_faillock.so preauth audit deny=3 unlock_time=60 even_deny_root
auth [default=die] pam_faillock.so authfail audit deny=3 unlock_time=60 even_deny_root
auth sufficient pam_faillock.so authsucc audit deny=3 unlock_time=60 even_deny_root
account required pam_faillock.so
# pam_tally2 --user USER --reset
# faillock --user USER --reset

20. Bostandoust.IR
#16
Auto Logout Inactive Users After a Period of Time
# vi /etc/profile.d/autologout.sh
TMOUT = 120
readonly TMOUT
export TMOUT
# chmod +x /etc/profile.d/autologout.sh

21. Bostandoust.IR
#17
Restrict “cron” / “at” Usage To Authorized Users
# rm -f /etc/cron.deny
# echo USER >> /etc/cron.allow
# rm -f /etc/at.deny
# echo USER >> /etc/at.allow

22. Bostandoust.IR
#18
Separate Disk Partitions For Better Security
/ defaults
/boot auto,nodev,nosuid,nouser,ro
/dev/shm auto,nodev,nosuid,nouser,rw
/home auto,nodev,nouser,rw
/root auto,nodev,nouser,rw
/tmp auto,nodev,noexec,nosuid,nouser,rw
/var auto,nodev,noexec,nosuid,nouser,rw
/var/log auto,nodev,noexec,nosuid,nouser,rw
/var/log/audit auto,nodev,noexec,nosuid,nouser,rw
/var/tmp auto,nodev,noexec,nosuid,nouser,rw
/usr auto,nodev,nouser,rw

23. Bostandoust.IR
#19
Enable and Set Users Disk Quota
/dev/vdb1 /home ext4 defaults,quota,usrquota,grpquota 0 0
/dev/vdb1 /home ext4 defaults,usrjquota=aquota.user, 0 0
grpjquota=aquota.group,jqfmt=vfsv1
# quotacheck -cugv /home
# quotaon -ugv /home
# edquota -u USER
# edquota -t
# repquota -as
# quota
# touch /forcequotacheck

24. Bostandoust.IR
#20
Find and Remove No-owner Files
# find / -nouser -nogroup

25. Bostandoust.IR
#21
Disable Unwanted SUID and SGID Binaries
# find / -perm /4000
# find / -perm /2000

26. Bostandoust.IR
#22
World-Writable Files / Directories and Sticky Bit
# find / -perm -2 -type d -ls
# find / -perm -2 -type f -ls
# find / -perm -2 ! -type l -ls
# chmod +t DIR

27. Bostandoust.IR
#23
Install and Use Antivirus
# yum install clamd clamav clamav-update clamav-data
# setsebool -P antivirus_can_scan_system 1
# setsebool -P antivirus_use_jit 1
# sed -i -e "s/^Example/#Example/" /etc/clamd.d/scan.conf
# sed -i -e "s/^Example/#Example/" /etc/freshclam.conf
# freshclam -d -c 4
# systemctl enable --now clamd@scan

28. Bostandoust.IR
#24
Install and Use Intrusion Detection System
# yum install aide
# aide --init
# cp -p /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz
# aide --check
# aide --update

29. Bostandoust.IR
#25
Install and Use Rootkit Detection Tools
# yum install rkhunter
# rkhunter --update
# rkhunter --propupd
# rkhunter --check --sk

30. Bostandoust.IR
#26
Install and Use Security Auditing Tools
# yum install lynis
# lynis audit system
# cat /var/log/lynis.log
# cat /var/log/lynis-report.dat | grep suggestion

31. Bostandoust.IR
#27
Install and Use Remote Logging System
rsyslog
syslog-ng

32. Bostandoust.IR
#28
Linux Auditing System (auditd)
# systemctl enable --now auditd
/var/log/audit/
/etc/audit/

33. Bostandoust.IR
#29
Install and Use Log Management and Monitoring Software
Nagios, Graylog2, Logcheck, Logwatch, Logstash
ELK Stack, LOGalyze, Zabbix

34. Bostandoust.IR
#30
Encrypt Network Data Communication
● File Transfer (scp, sftp)
● Messages, Files (GnuPG)
● VPN (openvpn)
● Websites (Apache with mod_ssl)
● Encryption-less (stunnel)

35. Bostandoust.IR
#31
Avoid Using TFTP, Telnet, Rlogin / Rsh
# yum erase xinetd ypserv tftp-server telnet-server rsh-server

36. Bostandoust.IR
#32
Enable and Use Firewall on Linux Server
# firewall-cmd
firewalld, iptables, ip6tables, arptables, ebtables, nft

37. Bostandoust.IR
#33
Turn Off IPv6 only if you are NOT using it
# echo install ipv6 /bin/true >> /etc/modprobe.conf
GRUB_CMDLINE_LINUX=”ipv6.disable=1”
# echo net.ipv6.conf.all.disable_ipv6 = 1 >> /etc/sysctl.conf

38. Bostandoust.IR
#34
Secure Access to OpenSSH Server
# vi /etc/ssh/sshd_config
HostbasedAuthentication no
ChallengeResponseAuthentication no
PasswordAuthentication no
PubkeyAuthentication yes
PermitEmptyPasswords no
IgnoreRhosts yes
PermitRootLogin no
X11Forwarding no
AllowUsers USER1 USER2

39. Bostandoust.IR
#35
Find, Investigate and Block Unused Ports
# netstat -tulpn
# ss -tulpn

40. Bostandoust.IR
#36
Set Timezone and Install Network Time Protocol
# timedatectl set-timezone Asia/Tehran
# yum install chrony
# systemctl enable --now chronyd
# chronyc tracking
# chronyc sources

41. Bostandoust.IR
#37
Physical and Pre-boot Server Security
Set BIOS Password
Do not allow Boot from External Media

42. Bostandoust.IR
#38
Set GRUB Password to Prevent “Single-User Mode” Boot
# grub2-setpassword
# cat /boot/grub2/user.cfg

43. Bostandoust.IR
#39
Encrypt Disk Drives using LUKS2
# yum install cryptsetup
# cryptsetup luksFormat /dev/sdX
# cryptsetup luksOpen /dev/sdX NAME
# cryptsetup luksDump /dev/sdX
# cryptsetup luksClose NAME

44. Bostandoust.IR
#40
Disable Ctrl+Alt+Delete to Prevent Interactive Reboot
# systemctl mask ctrl-alt-del.target
# systemctl daemon-reload

45. Bostandoust.IR
Question?

46. Bostandoust.IR
.‫باشید‬ ‫پیروز‬ ‫و‬ ‫موفق‬
sudo -u#-1 poweroff