liauw-media/system-architect

System Architect

Principles for security auditing and system hardening. Platform-specific commands in docs/security-audit/.

When to Use

• Setting up a new server
• Security audit before deployment
• After major configuration changes
• Periodic security checkups
• Investigating a breach

Core Principles

1. Defense in Depth

No single security measure is sufficient. Layer multiple controls.

Network → Firewall → Service → Application → Data
   ↓          ↓         ↓           ↓          ↓
 Block    Filter    Harden      Validate   Encrypt

2. Least Privilege

Grant minimum access required. Remove what's not needed.

3. Fail Secure

When things break, they should fail closed, not open.

4. Audit Everything

If you can't see it, you can't secure it. Log all access.

Priority Levels

All findings must be rated by severity:

| Level | Meaning | Action | |-------|---------|--------| | CRITICAL | Active exploitation possible | Fix NOW | | HIGH | Significant risk | Fix within 24h | | MEDIUM | Best practice violation | Fix within 1 week | | LOW | Minor improvement | Fix when convenient |

Audit Phases

Phase 1: Network Exposure

What can attackers reach?

• List all listening ports
• Check for services bound to 0.0.0.0
• Verify firewall is enabled and configured
• Identify unnecessary exposed services

Phase 2: Authentication

How do users and services authenticate?

• SSH: Key-based only, no root login
• Passwords: Strong policy, no empty passwords
• Services: No default credentials
• 2FA: Enabled where possible

Phase 3: Authorization

What can authenticated users do?

• Principle of least privilege
• No unnecessary sudo access
• Service accounts restricted
• File permissions reviewed

Phase 4: Data Protection

How is sensitive data protected?

• Encryption at rest
• Encryption in transit (TLS)
• Secrets management (not in code)
• Backup encryption

Phase 5: Monitoring

Can you detect attacks?

• Logging enabled
• Log aggregation
• Alerting configured
• Intrusion detection

Quick Audit Checklist

Network

• [ ] Firewall enabled
• [ ] Only necessary ports exposed
• [ ] Services bound to localhost where possible
• [ ] SSL/TLS properly configured

Authentication

• [ ] SSH key-based auth only
• [ ] Root login disabled
• [ ] Strong password policy
• [ ] fail2ban or similar installed

Services

• [ ] Running as non-root users
• [ ] Unnecessary services disabled
• [ ] Configurations hardened
• [ ] Auto-updates enabled

Docker (if applicable)

• [ ] Containers not privileged
• [ ] Ports bound to localhost
• [ ] No secrets in environment
• [ ] Images from trusted sources

Security Scanning

Public Tools (No Setup Required)

| Tool | Purpose | Usage | |------|---------|-------| | composer audit | PHP vulnerabilities | composer audit | | npm audit | Node vulnerabilities | npm audit | | pip-audit | Python vulnerabilities | pip-audit -r requirements.txt | | Trivy | Multi-language scanner | docker run aquasec/trivy fs . | | Gitleaks | Secrets in code | docker run zricethezav/gitleaks detect |

CI Integration

Add to your pipeline:

GitLab CI:

security:
  image: aquasec/trivy:latest
  script: trivy fs --exit-code 0 --severity HIGH,CRITICAL .
  allow_failure: true

GitHub Actions:

- name: Security scan
  run: |
    docker run aquasec/trivy:latest fs --severity HIGH,CRITICAL .
  continue-on-error: true

Output Format

================================================================================
SECURITY AUDIT REPORT
Date: YYYY-MM-DD
Host: hostname
================================================================================

CRITICAL (0)
------------
None found.

HIGH (2)
--------
[HIGH] Issue description
       Location: where
       Fix: how to fix

MEDIUM (1)
----------
[MEDIUM] Issue description
         Fix: how to fix

================================================================================
SUMMARY: 0 Critical | 2 High | 1 Medium | 0 Low
================================================================================

Documentation Integration

After completing an audit:

# Log summary
docchange "Security audit completed - X critical, Y high, Z medium issues"

# Log fixes
docchange "FIXED: Disabled SSH root login"

Reference Commands

Platform-specific audit commands:

| Platform | Location | |----------|----------| | Linux | docs/security-audit/linux.md | | Windows | docs/security-audit/windows.md | | Docker | docs/security-audit/docker.md |

Common Fixes

| Issue | Fix | |-------|-----| | SSH root login | PermitRootLogin no in sshd_config | | SSH password auth | PasswordAuthentication no in sshd_config | | No firewall | Enable ufw/firewalld/Windows Firewall | | Database exposed | Bind to 127.0.0.1 | | No fail2ban | Install and enable fail2ban | | Docker privileged | Remove --privileged flag | | Ports on 0.0.0.0 | Bind to 127.0.0.1:port:port |

Integration

Works with:

• server-documentation skill for logging
• defense-in-depth skill for layered security
• ci-templates skill for security scanning in CI