Approach (brief)
I’d follow a least-privilege, defense-in-depth checklist: minimize services, lock down configs, harden accounts and files, enforce logging/monitoring, and apply automated drift controls.
Configuration & access controls
- SSH: disable root login (PermitRootLogin no), use key-based auth, disable password auth (PasswordAuthentication no), restrict algorithms, enable AllowUsers/AllowGroups, change default port only as obfuscation, enable Fail2Ban/sshguard.
- Configure sudo to require password, limit NOPASSWD, use role accounts and RBAC where possible.
Service minimization
- Remove/stop/disable unnecessary packages and daemons (e.g., cups, avahi, ftp, telnet).
- Use systemd masking for high-risk services.
File permissions & accounts
- Enforce umask, secure /etc/ssh/authorized_keys, restrict /etc/sudoers (visudo), ensure /tmp, /var/tmp mounted with noexec,nosuid,nodev where feasible.
- Remove default accounts, lock inactive users, enforce strong password policy and PAM controls.
Patching & configuration management
- Enable automated security updates or scheduled patching, use CIS benchmarks, manage via Ansible/Chef for consistency.
Logging, monitoring, and auditing
- Centralize logs (rsyslog/Fluentd -> SIEM), enable auditd with rules for privileged actions, monitor auth logs, file integrity (AIDE/OSSEC), alerting for anomalies, retain logs securely.
Network & kernel hardening
- Configure firewall (ufw/iptables/nft) with deny-by-default, limit inbound services, rate-limit SSH, disable IPv6 if unused, enable SELinux/AppArmor, kernel tunables (sysctl) to harden networking.
How these reduce attack surface
- Fewer services = fewer exploitable code paths. Strict SSH and account controls reduce credential/remote compromise risk. File perms and mounts limit lateral privilege escalation. Centralized logging and FIM increase detection and response speed, turning unknown compromises into observable events. Configuration management and benchmarks ensure repeatable, auditable hardening so drift and misconfigurations are minimized.
