RHEL Security Hardening - Lock Down Your Linux Like You Actually Care About Security

RHEL ships with decent security defaults, but "decent" doesn't cut it when you're handling real data. Most admins install RHEL, run systemctl disable selinux, and call it a day. Then they wonder why their company made the news for the wrong reasons.

SELinux: Learn It or Lose It

SELinux documentation isn't bedtime reading, but it's the difference between a secure system and a fancy honeypot. The security hardening guide walks through proper configuration without the academic fluff.

I've seen production environments where SELinux caught privilege escalation attempts that would have owned the entire infrastructure. The CIS Benchmarks provide specific hardening criteria that actually work in real environments, not just compliance checkboxes.

The key is understanding that SELinux denials aren't errors - they're your system working correctly. ausearch -m AVC shows you what's being blocked. sealert -a /var/log/audit/audit.log explains why. The troubleshooting basics cover 90% of the issues you'll hit.

Firewall Configuration That Actually Makes Sense

Firewalld replaces iptables with something that doesn't require a CS degree to configure. The firewall documentation shows you how to set up zones without locking yourself out of SSH.

Start with firewall-cmd --get-default-zone to see what you're working with. The default public zone allows SSH and nothing else, which is fine for most servers. Add services with firewall-cmd --permanent --add-service=https and reload with firewall-cmd --reload.

The security compliance guide provides specific firewall rules that meet compliance requirements. For production environments, SCAP security profiles automate most of the configuration.

User and Access Management

Default sudo access is a security nightmare. The principle of least privilege isn't just a concept - it's what keeps your infrastructure intact. User management best practices cover role-based access that actually works.

Set up proper SSH key authentication and disable password logins. PasswordAuthentication no in /etc/ssh/sshd_config eliminates brute force attacks. The SSH hardening guide covers key-based auth and proper configuration.

For environments with compliance requirements, identity management with FreeIPA integrates with RHEL for centralized authentication. It's complex to set up but worth it for multi-system environments.

Kernel Parameter Tuning for Security

The kernel exposes thousands of tunable parameters through /proc/sys and sysctl. Most defaults are fine for general use but not for security-focused environments. The kernel administration guide covers the basics, but real hardening requires specific settings.

Key parameters for security hardening include network stack protection (net.ipv4.conf.all.send_redirects = 0), memory protections (kernel.dmesg_restrict = 1), and process restrictions (kernel.yama.ptrace_scope = 1). The Linux hardening guide provides comprehensive sysctl security configurations.

Create /etc/sysctl.d/99-security.conf with hardened parameters. Use sysctl -p /etc/sysctl.d/99-security.conf to apply without rebooting. The kernel security parameters guide explains each setting's security impact.

Audit System Configuration

Linux audit framework tracks security-relevant system events. Default configurations are minimal - production systems need comprehensive audit policies. The audit system documentation covers setup and configuration.

Install audit rules that track file access, privilege escalation, and network connections. Use auditctl -l to see active rules. Audit log analysis with ausearch identifies security events and policy violations. The security audit configuration provides CIS-compliant audit rules.

Warning: comprehensive auditing generates significant log volume. Size /var/log/audit appropriately and configure log rotation. Audit failures can bring systems down if not properly managed.

Network Security Hardening

Beyond firewalld, network stack hardening prevents various attack vectors. TCP SYN flood protection (net.ipv4.tcp_syncookies = 1), ICMP redirect rejection (net.ipv4.conf.all.accept_redirects = 0), and source routing prevention (net.ipv4.conf.all.accept_source_route = 0) are essential.

The network security guide covers protocol-specific hardening. For environments requiring DDoS protection, kernel parameters can limit connection rates and buffer sizes.

IPv6 introduces additional attack vectors. Unless specifically needed, disable with net.ipv6.conf.all.disable_ipv6 = 1. If IPv6 is required, apply equivalent hardening parameters for IPv6 stack.

Filesystem and Mount Point Security

Mount options significantly impact security. Use noexec on /tmp, /var/tmp, and /dev/shm to prevent execution from temporary directories. nosuid prevents SUID bit execution, nodev blocks device file creation.

Example /etc/fstab entries:

tmpfs /tmp tmpfs defaults,noexec,nosuid,nodev 0 0
tmpfs /var/tmp tmpfs defaults,noexec,nosuid,nodev 0 0
tmpfs /dev/shm tmpfs defaults,noexec,nosuid,nodev 0 0

The filesystem security guide explains mount option security implications. Separate partitions for /var, /var/log, and /tmp prevent disk space attacks from affecting core system functions.

Container and Virtualization Security

Container security on RHEL requires multiple layers of protection. Use rootless Podman for better isolation, SELinux container types (container_t) for mandatory access control, and read-only container filesystems where possible.

The container security documentation covers comprehensive container hardening. Use Red Hat's Universal Base Images instead of upstream containers for security and support guarantees.

For KVM virtualization, enable IOMMU (intel_iommu=on for Intel, amd_iommu=on for AMD) and use VirtIO devices for better performance and security. The virtualization security guide explains secure hypervisor configuration.

Automated Security Monitoring

Red Hat Insights provides automated security monitoring and vulnerability detection. It integrates with existing RHEL installations and provides actionable remediation guidance. The Insights security features explain vulnerability assessment capabilities.

For centralized logging, configure rsyslog to forward security events to a central log server. Use log analysis tools like ELK stack or Splunk for security event correlation. The logging and monitoring guide covers security-focused log management.

Implement file integrity monitoring for critical system files. AIDE (Advanced Intrusion Detection Environment) ships with RHEL and provides baseline comparison and change detection. Configure AIDE to monitor system binaries, configuration files, and sensitive data locations.