Baseline Configuration and Image Building
Immutable Infrastructure Immutable images built from CIS Benchmarks or DISA STIGs provide consistent, hardened baselines across all systems. Images should be built through CI/CD pipelines with reproducible builds. Golden images should be updated regularly with security patches and configuration improvements. Image versioning enables rollback to previous versions if issues arise. Immutable infrastructure prevents configuration drift by replacing systems rather than modifying them. Configuration changes require new image builds rather than in-place modifications. Minimal Attack Surface Minimal package installation reduces attack surface by eliminating unnecessary software. Only required packages should be installed, with regular reviews to remove unused packages. Unused services should be disabled to prevent exploitation. Service enumeration should occur regularly to identify and disable unnecessary services. Kernel parameters through sysctl should enforce security settings including Address Space Layout Randomization (ASLR), which randomizes memory addresses to prevent exploitation. Filesystem Hardening Filesystem mount options including noexec, nodev, and nosuid prevent code execution and device file creation on specific filesystems. Temporary directories should be mounted with noexec to prevent malware execution. Full-disk encryption protects data at rest from physical theft. Encrypted filesystems should be standard for all systems handling sensitive data. Secure /tmp configuration prevents symlink attacks and unauthorized file access. Separate /tmp filesystems with restrictive mount options provide additional security.Access Control and Identity
Account Management Shared accounts should be eliminated, with individual accounts for all users. Individual accounts enable attribution and accountability. SSH access should use SSO integration with short-lived certificates rather than long-lived keys. Certificate-based authentication enables centralized access control and automatic expiration. Password authentication should be disabled for SSH, requiring key-based or certificate-based authentication. Multi-factor authentication should be required for administrative access. Privilege Management PAM (Pluggable Authentication Modules) restrictions enforce password policies, account lockout, and session limits. PAM configuration should follow security best practices. Sudo should be configured for specific commands rather than full shell access where possible. Command-specific sudo reduces privilege escalation risks. Session recording for privileged operations provides audit trails for security investigations. Recording should capture all administrative actions.Patch and Configuration Management
Automated Patching Automated patch windows with canary deployments enable rapid patching with minimal risk. Canaries receive patches first, with monitoring for issues before broader deployment. Rollback procedures should be tested regularly, enabling rapid recovery from problematic patches. Automated rollback based on health checks reduces manual intervention. Emergency patch playbooks document how to rapidly deploy critical security patches outside normal windows. Emergency procedures should be tested regularly. Configuration as Code Configuration management through Ansible, Chef, Puppet, or Salt enables version-controlled, auditable configuration. Configuration as code prevents configuration drift and enables rapid deployment. Drift detection identifies systems with configurations that differ from desired state. Automated remediation can automatically correct drift. Configuration changes should be tested in non-production environments before production deployment. Testing prevents configuration errors from affecting production. Vulnerability Management Vulnerability management should be tied to Service Level Objectives (SLOs) defining maximum remediation times based on severity. Critical vulnerabilities may require remediation within 24 hours. Exceptions to patching requirements should be time-bounded with compensating controls. Exceptions should be reviewed regularly and eliminated when possible. Vulnerability scanning should occur continuously, identifying new vulnerabilities as they are disclosed. Scan results should integrate with patch management workflows.Logging and Monitoring
Comprehensive Audit Logging Centralized logging with tamper-evident storage prevents attackers from covering tracks. Logs should be forwarded to centralized systems in real-time. Kernel auditing through auditd captures system calls and security-relevant events. Audit rules should cover file access, process execution, and network connections. Process accounting logs all process executions, enabling investigation of malicious activity. Command logging for administrative sessions captures all commands executed. Endpoint Detection and Response EDR agents provide endpoint telemetry including process execution, network connections, and file modifications. EDR should be deployed with minimal performance impact. EDR alerts should integrate with incident response workflows, enabling rapid investigation and response. Alert tuning reduces false positives while maintaining detection coverage.Network Hardening
Host-Based Firewalls Default deny host firewalls block all traffic except explicitly allowed connections. Firewall rules should follow least privilege, allowing only required traffic. Egress filtering through proxies enables monitoring and control of outbound connections. Proxy logs provide visibility into external communications. Administrative interfaces should be locked down to specific source IP addresses or networks. Management interfaces should never be exposed to the internet. Network Segmentation Management networks should be isolated from production networks, preventing lateral movement from compromised production systems to management infrastructure. Network segmentation limits blast radius from compromises by preventing attackers from accessing all systems. Segmentation should align with trust boundaries.Cloud and Virtualization Hardening
Account Isolation Separate cloud accounts or projects per environment prevent development environment compromises from affecting production. Account isolation provides strong security boundaries. Service Control Policies (SCPs) or organization policies enforce guardrails across accounts, preventing insecure configurations. Policies should be tested before enforcement. Control Plane Security Control plane isolation from workloads prevents workload compromises from affecting infrastructure management. Control plane access should be strictly limited. Snapshot and image encryption protects data at rest in backups and templates. Encryption keys should be managed through KMS or HSM. Cross-account backup vaults provide additional protection by separating backup encryption keys from production keys.Container Host Hardening
Kernel Attack Surface Reduction Container hosts should be hardened to limit kernel attack surface. Minimal host operating systems including Container-Optimized OS or Bottlerocket reduce attack surface. AppArmor or SELinux mandatory access control provides additional containment beyond standard Linux permissions. MAC policies should be enforced for all containers. Runtime Security Containers should run with minimal runtime privileges, avoiding privileged containers where possible. Capabilities should be dropped to minimum required set. Read-only root filesystems prevent container modification, limiting attacker capabilities. Writable volumes should be minimized. Seccomp profiles restrict system calls available to containers, preventing exploitation of kernel vulnerabilities.Compliance and Validation
Baseline Compliance Automated compliance scanning validates that systems meet baseline requirements. Compliance violations should trigger alerts and remediation workflows. CIS Benchmarks provide industry-standard hardening guidelines for operating systems, databases, and applications. DISA STIGs provide government hardening standards. Continuous Validation Hardening should be validated continuously rather than point-in-time assessments. Continuous validation detects configuration drift and unauthorized changes. Penetration testing validates that hardening controls are effective against real attacks. Testing should occur regularly with findings driving hardening improvements.Conclusion
Infrastructure hardening requires systematic attack surface reduction, automated configuration management, and continuous compliance validation. Security engineers design hardening programs that balance security with operational efficiency through automation and immutable infrastructure. Success requires treating hardening as continuous process rather than one-time effort, with regular updates to baselines and rapid patching of vulnerabilities. Organizations that invest in infrastructure hardening fundamentals reduce breach impact while demonstrating security controls to auditors and customers.References
- CIS Benchmarks for Operating Systems and Applications
- DISA Security Technical Implementation Guides (STIGs)
- NIST SP 800-53 Configuration Management and Access Control Families
- NIST SP 800-123 Guide to General Server Security
- Cloud Provider Security Best Practices