Baseline AD against CIS Benchmarks

What “baseline AD against CIS” really means

CIS publishes benchmarks primarily by product/platform (for example, Windows Server). In an AD environment, those settings usually get enforced with domain-based Group Policy—especially for domain controllers (DCs) and member servers.

• Domain Controllers: Treat as a distinct security role with stricter settings and special operational constraints.
• Member Servers: Baseline depends on workload (file server, app server, SQL, etc.), but start with a common “member server baseline.”
• Workstations: Baseline separately (don’t reuse server/DC baselines).
• Exceptions: Allowed, but must be documented, approved, and continuously re-validated.

CIS Benchmarks are available for non-commercial use in PDF form, and CIS also provides assessment tooling (CIS-CAT Pro) to measure conformance programmatically. :contentReference[oaicite:0]{index=0}

Step 1: Pick the right CIS scope and “level”

Start by selecting the benchmark that matches each operating system and role (for example, your Windows Server version on DCs). CIS recommendations are commonly split into levels (often “Level 1” for broad compatibility, “Level 2” for tighter security with more potential impact).

Baseline selection checklist

• Inventory: OS versions for DCs, member servers, and clients.
• Role separation: DC baseline is not the same as member server baseline.
• Compatibility target: Begin with Level 1 for your first pass, then add Level 2 where justified.
• Regulatory overlay: If you must meet additional requirements (e.g., a regulator), track those as “add-ons,” not replacements.

Note: Windows CIS Benchmarks are written with AD domain-joined management in mind (i.e., via Group Policy). :contentReference[oaicite:1]{index=1}

Step 2: Convert CIS recommendations into GPO-friendly building blocks

In AD, “baseline” should translate into a small number of clearly-scoped GPOs that are easy to understand, test, and roll back. Avoid the trap of one mega-GPO that nobody can safely touch.

Recommended baseline GPO layout

• Domain Account Policies (linked at the domain root): password policy, lockout policy, Kerberos policy.
• DC Baseline (linked to the Domain Controllers OU): security options, audit policy, user rights assignments, services, firewall, etc.
• Member Server Baseline (linked to server OUs): shared server hardening items.
• Workstation Baseline (linked to workstation OUs): client hardening items.
• Role “delta” GPOs (per workload): special settings needed only for certain servers.

If you want a refresher on how GPOs work and how to manage them cleanly, start here: Active Directory Group Policy and Managing GPOs with Group Policy Management Console (GPMC).

Step 3: Establish the “golden” configuration source of truth

Your baseline must be portable and reviewable. That usually means storing GPO backups (and any scripts/templates) in version control, along with documentation and exception records.

Practical source-of-truth model

1. GPO Backups: Export baseline GPOs routinely (and on every approved change).
2. Policy diffing: Track what changed, when, and why.
3. Exception ledger: Each exception includes: CIS reference (or category), business reason, approval, compensating control, expiry/review date.

Tip: Microsoft’s Security Compliance Toolkit (SCT) can help you download, analyze, compare, and manage Microsoft-recommended security baselines and GPO backups—useful as a second reference point alongside CIS. :contentReference[oaicite:2]{index=2}

Step 4: Implement safely using “staging OUs” and ringed rollouts

Never drop a CIS-aligned baseline onto all DCs or all servers in one move. Use a staged approach:

Rollout rings (recommended)

• Ring 0 (Lab): A domain you can break.
• Ring 1 (Pilot): A small set of representative systems (including at least one DC if possible).
• Ring 2 (Broad): A controlled wave by OU/site.
• Ring 3 (Enforcement): Full coverage + drift detection alerts.

What to test before broad rollout

• Authentication flows (Kerberos/NTLM where required, SSO, legacy apps)
• Administrative workflows (remote admin, MMCs, WinRM, management agents)
• File/print, RDP, and service-to-service comms
• Event logging volume and SIEM ingestion capacity

Step 5: Measure compliance (don’t guess)

A baseline only matters if you can prove it’s applied and detect drift. CIS-CAT Pro Assessor is designed to turn CIS Benchmark recommendations into actionable assessments by scanning systems and reporting compliance. :contentReference[oaicite:3]{index=3}

Measurement model

1. Initial scan: Establish the gap between current state and target baseline.
2. Remediation pass: Fix high-impact, low-risk items first.
3. Re-scan: Confirm your changes actually moved the needle.
4. Continuous drift checks: Schedule repeat scans, especially for DCs and Tier-0 assets.

If you’re building a detection-and-response culture, make sure your auditing and logs are aligned too: PowerShell auditing: an IT admin’s security guide.

Step 6: Focus first on the CIS areas that matter most to AD security

CIS Benchmarks contain many items. In AD environments, these categories usually deliver the fastest security payoff:

1) Account and authentication policies

• Password policy (length, complexity, rotation strategy)
• Account lockout policy
• Kerberos policy tuning (careful: changes can break legacy systems)

Practical walkthrough: Configure domain password policy – Here’s how.

2) Privilege governance (groups, rights, and delegation)

• Minimize membership in Tier-0 groups
• Audit and reduce nested group sprawl
• Lock down “user rights assignment” (log on locally, debug programs, etc.)

Practical walkthrough: Auditing Nested Group Memberships: An Expert Guide.

3) Logging and audit policy that supports investigations

• Advanced Audit Policy categories aligned to your detection goals
• Central collection from DCs and Tier-0 servers
• Retention based on incident response and compliance needs

4) Hardening “high-leverage” security options

• SMB hardening (signing where required), stronger channel protections where supported
• UAC behavior for admin elevation on servers and admin workstations
• Reduce legacy protocols and weak crypto where business allows

5) Operational security controls

• Secure remote administration patterns (tiering, jump hosts, least privilege)
• Controlled local admin management (LAPS / modern alternatives)
• Patch cadence and change control tied to baseline drift checks

Step 7: Handle exceptions like an auditor (and an attacker) would

Exceptions are normal. Unmanaged exceptions are how baselines die.

Exception record template

• Benchmark reference: which recommendation/category you’re not meeting
• System scope: which OU/hosts/app owners
• Business reason: why the deviation is required
• Compensating control: monitoring, segmentation, MFA, restricted admin paths, etc.
• Expiry/review date: force periodic reassessment
• Approval: name/role/ticket link

Step 8: Keep the baseline alive (drift control)

The most secure baseline is useless if it only exists on paper. “Drift” happens when: admins change GPOs under pressure, new servers appear outside the right OUs, or upgrades introduce new defaults.

Baseline maintenance loop

1. Monthly: DC/member server compliance scans + report
2. Weekly: change review of baseline-linked GPOs
3. Per change: re-scan after patch cycles, DC upgrades, schema changes, or major app rollouts
4. Per incident: use findings to tighten baseline and improve monitoring

Quick-start plan (if you need a practical sequence)

1. Inventory DC OS versions and choose the matching CIS benchmark scope (start with Level 1).
2. Create a DC Baseline GPO and link it only to a pilot DC OU (staging).
3. Set domain account policies (password/lockout/Kerberos) deliberately and validate auth flows.
4. Run compliance scans (CIS-CAT where available) and produce a gap report.
5. Remediate in waves: high-impact/low-risk first; document exceptions; re-scan.
6. Roll out to broader OUs/sites; turn on drift checks and change governance.