All data transmitted over a network is open to monitoring.
Encrypt transmitted data whenever possible with password or using keys / certificates.
GnuPG allows to encrypt and sign your data and communication, features a versatile key management system as well as access modules for all kind of public key directories.
SSH / RSYNC / SFTP for file transfer
SSL whenever it's possible
2. Avoid Using FTP, Telnet, and Rlogin / Rsh Services
Commands and transferred files can be captured by anyone on the same network using a packet sniffer.
Use instead OpenSSH , SFTP, or FTPS (FTP over SSL)
3. Minimize Software to Minimize Vulnerability
yum list installed
yum list packageName
or
dpkg --list
dpkg --info packageName
4. One Network Service Per System, VM or Container
Run each exposed service isolated via VM, Docker, LXC..
5. Keep Linux Kernel and Software Up to Date
6. Use Linux Security Extensions
7. SELinux
8. Linux User Accounts and Strong Password Policy
9. Set Up Password Aging for Better Security
10. Restrict Use of Previous Passwords
11. Lock User Accounts After Login Failures
12. Verify No Accounts Have Empty Passwords
13. Ensure No Non-Root Accounts Have UID Set to 0
14. Disable Root Login
15. Physical Server Security
16. Disable Unwanted Linux Services
17. Find Listening Network Ports
18. Delete X Window Systems (X11)
19. Configure Iptables and TCPWrappers Based Firewall
20. Harden Linux Kernel with /etc/sysctl.conf
21. Separate Disk Partitions for Linux System
22. Implement Disk Quotas
23. Disable IPv6 if Not Using It
24. Disable Unwanted SUID and SGID Binaries
25. Check for World-Writable Files
26. Remove Noowner Files
27. Use Centralized Authentication Service
28. Implement Kerberos for Authentication
29. Configure Logging and Auditing
30. Monitor Suspicious Logs with Logwatch / Logcheck
31. Use System Accounting with auditd
32. Secure OpenSSH Server
33. Install and Use Intrusion Detection Systems (IDS)
