Any serious systems can’t ignore server security, especially in public Cloud. No doubt there’re tons of tips and tutorials available on the Internet. Let’s focus on fundamental and general best practices first.
A List Of Security Improvements I Enforce After OS Provisioning.
Original Article: http://dennyzhang.com/linux_security
Here we use Ubuntu 16.04 for instance.
1. Keep Kernel Up-To-Date.
Certainly no blind update for prod envs. But for newly installed servers, it’s usually harmless and can guarantee a higher level of security.
One common suggestion is disabling unused services. But I choose to trust my distros provider. Generally speaking, I believe they might make right choices to have what installed and enabled by default.
apt-get -y update
2. Reset Root password.
We need that to access web console of VMs. This happens when ssh doesn’t work. e.g. problematic iptables rules block you, OS runs into kernel panic, or machine reboot mysteriously stucks.
root_pwd="DevOpsDennyChangeMe1" echo "root:$root_pwd" | chpasswd
3. Hardening SSHD.
Only allow ssh by keyfile, thus hackers can’t easily break-in by guessing your password. Use another ssh listening port other than 22, which can avoid annoying ssh login attempts.
# Disable ssh by password sed -i 's/^#PasswordAuthentication yes/PasswordAuthentication no/g' /etc/ssh/sshd_config sed -i 's/PasswordAuthentication yes/PasswordAuthentication no/g' /etc/ssh/sshd_config grep PasswordAuthentication /etc/ssh/sshd_config # Use another ssh port sshd_port="2702" sed -i "s/^Port 22/Port $sshd_port/g" /etc/ssh/sshd_config grep "^Port " /etc/ssh/sshd_config # Restart sshd to take effect service ssh restart
4. Restrict Malicious Access By Firewall.
This might be the most important security improvement you shall do.
# Have a clean start with iptables iptables -F; iptables -X echo 'y' | ufw reset echo 'y' | ufw enable ufw default deny incoming ufw default deny forward # Allow traffic of safe ports ufw allow 22,80,443/tcp # Allow traffic from certain port ufw allow 2702/tcp # Allow traffic from trusted ip ufw allow from 52.74.151.55
5. Add Timestamp To Command History.
It allows us to review what commands has been issued, and when.
echo export HISTTIMEFORMAT="%h %d %H:%M:%S " >> /root/.bashrc
6. Generate SSH Key Pair.
Never never share the same ssh key pair across servers!
exec ssh-agent bash # General new key pair ssh-keygen # Load key pair ssh-add
7. Pay Close Attention to var/log.
Use logwatch to automate the check and analysis. It’s a userful parsing perl script that analyzes and generates daily reports on your system’s log activity. Major log files:
- /var/log/kern.log
- /var/log/syslog
- /var/log/ufw.log
- /var/log/auth.log
- /var/log/dpkg.log
- /var/log/aptitude
- /var/log/boot.log
- /var/log/cron.log
- /var/log/mailog
apt-get install -y logwatch # Full check. Takes several minutes logwatch --range ALL # Only check log of Today logwatch --range Today # Check log for last week logwatch --range "between -7 days and -1 days"
8. Run 3rd Security Check Tools.
Not everyone can or will be a security expert. Better try reliable and versatile tools. lynis is quite handy and straight-forward. Just a single bash file.
apt-get install -y lynis # Run lynis to check security issues lynis -c
9. Proper Backup Unrecoverable Data.
Always has plan B. As the last resort, make it’s feasible to do a quick system restore in new servers.
Special thanks to this reddit discussion.
More Reading: Detect Suspicious Linux Processes
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