Organisations should tailor a baseline by recording approved exceptions, additions, and reductions for a specific system or environment. Each change should have a risk-based reason, an owner, and review dates. Avoid weakening the baseline without evidence, and make sure tailored settings remain consistent with policy, mission needs, and audit expectations.
What baseline tailoring actually changes
baseline tailoring is not a free-form rewrite of a standard baseline. It is a controlled change process that records why a control is being adjusted for a particular system, environment, or mission need. The point is to preserve the strength of the baseline while making the documented exception, addition, or reduction traceable and reviewable.
A good tailored baseline stays anchored to the original security intent. If the original control was chosen to reduce a specific exposure, the tailoring should explain how that exposure is still handled, whether by a compensating control, a different implementation, or a formally accepted gap.
How to approve exceptions, additions, and reductions
Tailoring works best when each change is treated as a decision, not an edit. Record the exact control being changed, the rationale, the approving owner, and the review date so the organisation can tell the difference between an approved deviation and an accidental drift from policy.
Use the smallest change necessary to meet the documented need. Additions should address a real requirement, reductions should be limited to what the system genuinely cannot support, and exceptions should be time bound wherever possible. For baseline selection and tailoring concepts in a control-catalogue context, the NIST SP 800-53 Guide is the most direct internal reference.
Baseline tailoring should also line up with hardening expectations for the platform in use. If the tailored baseline weakens a general configuration requirement, compare it against a known secure configuration standard such as CIS Benchmarks so the change is explicit and defensible rather than informal.
What good tailoring looks like in practice
Effective tailoring is visible in documentation and in operations. The tailored baseline should still be understandable to assessors, operators, and auditors, and it should remain consistent with the organisation’s policy, system categorisation, and mission requirements. If a setting changes, the reason for the change should be easy to trace back to a business or security requirement.
Well-run teams also treat review dates as real control points. A tailored baseline that has not been revisited after a system change, major incident, or environment expansion can silently become outdated, especially when new dependencies, integrations, or user groups are added later.
That discipline is strongest when tailoring is tied to the broader control catalogue and assessment process, not managed as a one-off exception list. The control set in NIST SP 800-53 Rev 5 Security and Privacy Controls is designed to support that kind of documented adjustment and review.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
NIST SP 800-53 Rev 5 and CIS Controls v8 set the technical controls, while ISO/IEC 27001:2022 defines the regulatory obligations.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-53 Rev 5 | CM-2 — Baseline Configuration | Tailoring directly changes system baselines and documented variants. |
| CM-3 — Configuration Change Control | Tailoring is a controlled change that needs approval, rationale, and review. | |
| CA-7 — Continuous Monitoring | Tailored settings need recurring review to ensure exceptions stay valid over time. | |
| Recommendation — Document approved deviations from the baseline and keep them version-controlled. Require formal approval for every baseline change and record the business justification. Monitor tailored controls on a schedule and reassess exceptions after environment changes. | ||
| ISO/IEC 27001:2022 | A.8.9 — Configuration management | Tailoring is configuration control applied to security settings and baselines. |
| Recommendation — Maintain approved configuration baselines and track deviations as controlled changes. | ||
| CIS Controls v8 | CIS-4 — Secure Configuration of Enterprise Assets and Software | Baseline tailoring is the core practice of managing secure configurations by exception. |
| Recommendation — Use hardened baselines and document every approved deviation from them. | ||
Practitioner Guidance
What to verify: Before approving a tailored baseline, verify that each change has a named owner, an explicit risk reason, and a scheduled review date. If the rationale cannot be stated in operational terms, the tailoring is probably too vague to defend.
Decision rule: If the change reduces the baseline requirement, ask what compensating control or acceptance statement preserves the original security outcome. If no credible substitute exists, treat the change as an unproven weakening rather than a valid tailoring decision.
Practitioner takeaway: The safest tailoring decisions are the ones that remain auditable months later, because the real test is not whether the change was convenient, but whether the organisation can still justify it when the environment, owner, or auditor changes.