Linux Server Hardening - Secure Your Servers Against Modern Threats
Professional Linux server hardening that goes beyond default configurations. I audit and secure SSH, firewalls, kernel parameters, mandatory access controls, and service exposure following CIS benchmarks.
Linux server hardening transforms a default installation into a secure, attack-resistant system. Out-of-the-box Linux configurations prioritize compatibility over security, leaving SSH with password authentication, unnecessary services running, and permissive firewall rules. My Linux server hardening service audits your entire configuration against CIS benchmarks and industry best practices, then implements the hardening measures that reduce your attack surface without breaking your applications.
Default Linux Configurations Are Insecure
SSH Is Your Biggest Attack Surface
Default SSH configurations allow password authentication, root login, and listen on port 22. Automated brute-force bots hammer these defaults millions of times per day. Without SSH hardening, it's only a matter of time.
Unnecessary Services Running
Default Linux installations enable services you don't need: Avahi, CUPS, NFS, rpcbind, and others. Each running service is an attack surface. If it's not needed, it should not be running.
Weak Access Controls
Default sudoers configurations, shared service accounts, and missing SELinux/AppArmor policies make privilege escalation trivial for an attacker who gains initial access.
What My Linux Server Hardening Covers
SSH Lockdown
Key-only authentication, disabled root login, IP whitelisting, port change, connection rate limiting, and fail2ban configuration. I close the most targeted attack vector first.
Firewall Architecture
Proper iptables/nftables rules with default-deny policies, rate limiting, and logging. Only explicitly required ports are open, with source IP restrictions where applicable.
Kernel Hardening
sysctl tuning for network stack protection (SYN cookies, ICMP restrictions, IP spoofing prevention), ASLR enforcement, and core dump restrictions.
Mandatory Access Controls
SELinux or AppArmor configuration to confine services and limit the blast radius of a compromise. Even if an attacker gains access to a service, MAC policies block lateral movement.
CIS Benchmark Alignment
Every hardening measure is mapped to CIS Benchmark controls for Ubuntu, Debian, RHEL, or CentOS. You get documentation that satisfies compliance auditors.
Audit Logging and Monitoring
Auditd configuration for file access, privilege escalation, and login events. Logrotation setup and guidance on centralized log shipping for SIEM integration.
The Linux Server Hardening Process
Baseline Assessment
I audit the current server configuration: OS version, running services, open ports, user accounts, sudo configuration, and installed packages.
CIS Benchmark Gap Analysis
Automated and manual CIS benchmark scoring identifies every deviation from security baselines with severity ratings.
Hardening Implementation
I implement all hardening measures: SSH lockdown, firewall rules, service disabling, kernel tuning, filesystem permissions, and MAC policies.
Application Compatibility Testing
After hardening, I verify all your applications and services still function correctly. Hardening should not break production workloads.
Documentation and Handover
Complete documentation of every change made, configuration files, and a maintenance runbook for ongoing security.
Hardening Deliverables
SSH Hardening
sshd_config lockdown, key-only auth, fail2ban configuration, and connection rate limiting.
Firewall Rules
iptables/nftables ruleset with default-deny policy, documented exceptions, and rate limiting.
Kernel Security Tuning
sysctl.conf hardening for network stack, memory protection, and filesystem security.
MAC Policy Configuration
SELinux or AppArmor profiles for all running services with enforcement mode enabled.
CIS Compliance Report
Before/after CIS benchmark scores with every control documented.
Maintenance Runbook
Ongoing maintenance procedures: patching strategy, log review, and configuration drift detection.
Frequently Asked Questions About Linux Server Hardening
Will server hardening break my applications?
No. I test all changes against your running applications before finalizing. Hardening is applied incrementally, with each change verified for compatibility. If a hardening measure conflicts with a legitimate application requirement, I document the exception and implement compensating controls instead.
Which Linux distributions do you support?
I support Ubuntu Server, Debian, RHEL, CentOS Stream, Rocky Linux, AlmaLinux, and Amazon Linux. CIS Benchmarks are available for all these distributions, and I adapt hardening procedures to each distribution’s package management and service management systems.
Do you harden cloud servers (AWS, Azure, GCP)?
Yes. Cloud instances need OS-level hardening in addition to cloud security groups and IAM policies. I harden the Linux OS inside the instance and review cloud-level security settings to ensure both layers work together.
How long does Linux server hardening take?
A single server typically takes 2-3 business days including assessment, hardening, testing, and documentation. Multiple servers with identical configurations can be done faster using automation. Complex environments with many services require additional time for compatibility testing.
Should I use SELinux or AppArmor?
SELinux is more powerful and is the default on RHEL-based distributions. AppArmor is easier to configure and is the default on Ubuntu/Debian. I recommend using whichever your distribution ships with and configure it properly rather than switching, unless you have specific compliance requirements.
Harden Your Linux Servers Before the Next Attack
Default Linux configurations are designed for ease of setup, not security. Every day your servers run unhardened, they're vulnerable to automated attacks, brute force, and privilege escalation. Let me lock them down properly.
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