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ntlm_hardening

🔐 NTLM Hardening & Kerberos Transition

Objectives:

  • Perform a comprehensive discovery of all systems and applications using NTLM authentication.

  • Identify systems capable of supporting Kerberos and prioritize candidates for transition.

  • Create a phased implementation plan to eliminate NTLM reliance.

  • Harden Active Directory and enforce Kerberos as the preferred authentication protocol.

  • Reduce lateral movement risks and meet modern authentication security standards.

  1. Discovery & NTLM Usage Inventory
    • Enabled NTLM audit policies via Group Policy:
      • Audit NTLM authentication in this domain
      • Audit NTLM authentication to remote servers
    • Parsed Domain Controller event logs for:
      • Event IDs 4624, 4776, and 8004
      • NTLMv1 usage warnings and fallback authentication attempts
    • Used PowerShell scripts to correlate:
      • Source hosts and user accounts using NTLM
      • Applications, services, and legacy devices triggering NTLM authentication
    • Collected and categorized data into exportable NTLM usage reports for review and remediation planning

  2. Classification & Kerberos Readiness Planning
    • Reviewed each system and application for Kerberos support
    • Tagged and exported systems into readiness tiers:
      • Fully Kerberos-capable
      • Requires configuration updates
      • NTLM-only with legacy dependencies
    • Identified:
      • Systems missing proper SPN (Service Principal Name) configurations
      • Non-domain-joined assets requiring isolation or special handling
      • Validated readiness plans with application owners and infrastructure teams

  3. Test Deployment & Controlled Rollout
    • Created an isolated test environment reflecting production dependencies
    • Applied GPOs to enforce:
      • Kerberos-only authentication on test clients and servers
      • AES-based encryption while disabling fallback RC4
    • Validated authentication behavior across:
      • Windows and Linux (RHEL) systems
      • Shared drives, application tiers, and service accounts
    • Logged and tracked Kerberos ticket usage and authentication failures
    • Deployed exception handling for systems still undergoing transition

  4. Full Deployment & Enforced Controls
    • Rolled out hardened GPOs in stages to production environments:
      • Restrict NTLM: Deny for domain accounts to remote servers
      • Restrict NTLM: Deny for non-domain accounts
    • Enforced Kerberos hardening policies:
      • AES256-SHA1 encryption requirement
      • Enabled FAST (Flexible Authentication Secure Tunneling)
    • Replaced or reconfigured systems with NTLM-only dependencies
    • Validated proper SPN registrations and rotated service account credentials

  5. Hypercare & Post-Cutover Monitoring
    • Continuously monitored domain controllers for authentication failures
    • Reviewed NTLM audit logs to identify new or missed fallback usage
    • Alerted on any unexpected authentication patterns
    • Maintained rollback playbooks and exception GPOs for high-impact services
    • Documented Kerberos transition paths, SPN configurations, and protocol enforcement for auditing and operational continuity

Result:

This effort successfully eliminated NTLM usage within the environment and ensured:

  • Stronger authentication posture using Kerberos ticketing
  • Reduced risk of credential-based attacks (e.g., pass-the-hash)
  • Better visibility into authentication behaviors and failures
  • Compliance with internal security standards and industry best practices
  • Readiness for future initiatives including smart card auth, MFA, and Zero Trust integration