This document defines the security policies, procedures, and best practices for the Linux Core Security project.

1. Overview
2. Automated Patching Policy
3. Update Compatibility Policy
4. Continuous Security Improvement Policy
5. Core Protection Mechanisms
6. Incident Response
7. Compliance

This project implements defense-in-depth security for Linux systems through:

• Kernel hardening and memory protection
• Mandatory access control (AppArmor)
• Continuous monitoring and auditing
• Automated security patching
• File integrity monitoring

1. Least privilege - processes run with minimum required permissions
2. Defense in depth - multiple layers of security controls
3. Fail secure - system defaults to secure state on failure
4. Audit everything - comprehensive logging of security events
5. Automate security - reduce human error through automation

This policy applies to all security updates for the operating system, kernel, and installed packages.

Updates are classified into the following categories:

1. CRITICAL - Remote code execution, privilege escalation

   • Apply within 24 hours
   • Emergency patching procedure applies

2. HIGH - Authentication bypass, data exposure

   • Apply within 72 hours
   • Standard patching procedure applies

3. MEDIUM - Denial of service, information disclosure

   • Apply within 7 days
   • Standard patching procedure applies

4. LOW - Minor security issues

   • Apply within 30 days
   • Scheduled maintenance window

Automated patching runs daily at 03:00 UTC:

• Security updates: Applied automatically
• Kernel updates: Staged, requires approval for reboot
• Application updates: Applied during maintenance window

1. Pre-patch validation

   • Run compatibility check script
   • Create system snapshot
   • Verify backup status

2. Patch application

   • Download and verify packages
   • Apply updates in minimal steps
   • Log all changes

3. Post-patch verification

   • Verify critical services
   • Run security scan
   • Update documentation

If patching causes issues:

1. Identify affected packages from logs
2. Restore from pre-patch snapshot
3. Document issue and root cause
4. Report to security team
5. Create exception until fix available

The following packages require manual approval:

• Kernel updates (linux-image-*)
• Container runtime (docker, containerd)
• Critical infrastructure (systemd, openssh)

• Unattended upgrades: configs/unattended-upgrades/50unattended-upgrades
• Auto-patch script: scripts/auto-patch.sh
• Systemd timer: systemd/auto-patch.timer

Before applying any update, the system performs:

1. Dependency conflict check

   • Verify no package conflicts
   • Check version constraints
   • Validate repository signatures

2. Kernel compatibility check

   • Verify module compatibility
   • Check driver requirements
   • Validate boot configuration

3. Configuration file analysis

   • Identify files to be modified
   • Backup existing configurations
   • Plan merge strategy

4. Service impact assessment

   • Identify affected services
   • Plan restart sequence
   • Estimate downtime

Updates follow a staged deployment:

1. Development environment (immediate)
2. Staging environment (24 hours later)
3. Production environment (72 hours after staging)

Maintain compatibility with:

• Ubuntu 22.04 LTS and 24.04 LTS
• Debian 11 (Bullseye) and 12 (Bookworm)
• Kernel versions 5.15 LTS and 6.1 LTS or newer
• Docker 24.x and newer
• Containerd 1.6.x and newer

When a breaking change is detected:

1. Halt automatic updates
2. Notify security team
3. Assess impact and alternatives
4. Create migration plan
5. Schedule maintenance window
6. Execute with rollback ready

• Compatibility checker: scripts/compatibility-check.sh
• Pre-update snapshot: scripts/pre-update-snapshot.sh

1. Identification

   • Daily automated scans (Trivy, Lynis)
   • CVE monitoring and alerts
   • Threat intelligence feeds

2. Assessment

   • CVSS score evaluation
   • Exploitability analysis
   • Business impact assessment

3. Remediation

   • Patch if available
   • Apply compensating controls
   • Document exceptions

4. Verification

   • Confirm fix effectiveness
   • Update security baselines
   • Close vulnerability ticket

Track and report on:

• Mean time to patch (MTTP)
• Vulnerability count by severity
• Security incident count
• Compliance score
• Failed login attempts
• Suspicious activity detections

1. Collect security metrics and findings
2. Analyze trends and patterns
3. Identify improvement opportunities
4. Prioritize based on risk
5. Implement changes
6. Measure effectiveness
7. Document lessons learned

• Review security policies quarterly
• Update documentation continuously
• Share threat intelligence
• Conduct post-incident reviews

ASLR (Address Space Layout Randomization):

• Full randomization enabled: kernel.randomize_va_space = 2
• Randomizes stack, heap, libraries, and mmap regions
• Verified at boot and monitored continuously

Stack Protection:

• Stack canaries enabled in kernel
• NX bit enforced for non-executable stack
• PIE (Position Independent Executables) required

Configuration: configs/sysctl.d/99-security.conf

Kernel Self-Protection:

• kASLR enabled
• Kernel page-table isolation (KPTI)
• SMEP/SMAP when hardware supports

System Call Hardening:

• Seccomp filtering enabled
• Restricted ptrace access
• Disabled kexec for security

Dangerous Features Disabled:

• SysRq key disabled
• Core dumps restricted
• Kernel module loading restricted

Mandatory Access Control:

• AppArmor enforcing mode
• Custom profiles for all services
• Default deny policy

Process Isolation:

• Namespace separation
• CGroups resource limits
• Capability dropping

Filesystem Protection:

• Protected symlinks and hardlinks
• Protected FIFOs and regular files
• Secure mount options (noexec, nosuid, nodev)

Configuration: configs/apparmor.d/

Hardware Support:

• AMD SME/SEV when available
• Intel TME when available

Software Measures:

• Encrypted swap partition
• Memory wiping on process exit
• Secure memory allocation

Configuration: scripts/memory-protection.sh

Audit System:

• Comprehensive auditd rules
• Privileged command monitoring
• File access logging
• Network connection tracking

File Integrity:

• AIDE baseline monitoring
• Daily integrity checks
• Alert on unauthorized changes

Log Management:

• Centralized logging
• Log integrity protection
• Retention policy: 90 days

Configuration: configs/auditd/audit.rules, configs/aide/aide.conf

1. P1 - Critical

   • Active exploitation
   • Data breach
   • System compromise Response: Immediate

2. P2 - High

   • Attempted exploitation
   • Suspicious activity
   • Policy violation Response: Within 4 hours

3. P3 - Medium

   • Vulnerability detected
   • Configuration drift
   • Anomalous behavior Response: Within 24 hours

4. P4 - Low

   • Minor policy violation
   • Information request Response: Within 72 hours

1. Detection and triage

   • Identify scope and severity
   • Classify incident
   • Assign response team

2. Containment

   • Isolate affected systems
   • Preserve evidence
   • Block attack vectors

3. Eradication

   • Remove malware/backdoors
   • Patch vulnerabilities
   • Reset credentials

4. Recovery

   • Restore from clean backup
   • Verify system integrity
   • Resume operations

5. Post-incident

   • Root cause analysis
   • Update defenses
   • Document lessons learned

Security Team: security@example.com Emergency: On-call security rotation Escalation: Security leadership

This configuration supports compliance with:

• CIS Benchmarks for Ubuntu/Debian
• NIST Cybersecurity Framework
• SOC 2 Type II
• PCI DSS (where applicable)
• HIPAA (where applicable)

All security-relevant events are logged:

• Authentication events
• Authorization decisions
• Configuration changes
• Administrative actions
• Security alerts

Logs are:

• Tamper-protected
• Centrally collected
• Retained for 90 days minimum
• Available for forensic analysis

Maintain documentation for:

• Security configurations
• Change history
• Incident reports
• Exception requests
• Audit findings

To report a security vulnerability:

1. Email: security@example.com
2. Include:
   • Description of vulnerability
   • Steps to reproduce
   • Potential impact
   • Suggested fix (if any)

Do not:

• Publicly disclose before patch
• Access data beyond demonstration
• Perform destructive testing

Response timeline:

• Acknowledgment: 24 hours
• Initial assessment: 72 hours
• Fix timeline: Based on severity

Version: 1.0 Last Updated: 2024 Review Frequency: Quarterly Owner: Security Team