NIST SP 800-53 Rev. 5 SC-31(1) — Test Covert Channels For Exploitability

What this control requires

Test a subset of identified covert channels to assess which channels are exploitable. This testing helps determine the actual risk posed by covert channels and whether they can be used for unauthorized information flow across security domains. It is essential to evaluate covert channels in systems that handle sensitive or export-controlled information. This control supports the Covert Channel Exploitability Testing System capability within the System and Communications Protection family.

In plain English

Test a subset of identified covert channels to assess which channels are exploitable. In practice, this means you can prove you policy management-level controls on a defined cadence.

Why it matters

SP 800-53 is the catalogue every U.S. federal authorisation (FedRAMP, FISMA, CMMC) and most regulated industries point at. A missing control surfaces as a Plan of Action & Milestones (POA&M) item that an Authorizing Official must approve before the Authority To Operate is granted or renewed.

This control is rated high. Auditors expect a named owner, a remediation SLA, and a tooling artefact that evidences continuous operation.

What an auditor looks for

A 3PAO (FedRAMP) or Independent Assessor (NIST RMF) tests against NIST SP 800-53A assessment procedures. For each control they expect a documented implementation that addresses every assessment objective (Examine, Interview, Test) and an implementation summary in the System Security Plan.

Within System and Communications Protection, the assessor will trace your implementation back to the catalogue reference (Control SC-31(1)) and look for objective evidence on the latest two assessment cycles.

How to implement

Code Review Testing

Pipeline. Require at least one human reviewer plus passing CI (lint, type, unit, security scan) before merge — protected branches enforce this.

Policy Management

Docs. Keep each policy in version-controlled Markdown alongside the code that implements it; ship a signed PDF snapshot at each annual review and link the SHA into the SoA.

Operational checklist

• Policy. Document the trigger, the owner and the cadence.
• Information. Document the trigger, the owner and the cadence.
• Security. Document the trigger, the owner and the cadence.
• Review. Document the trigger, the owner and the cadence.
• Protection. Document the trigger, the owner and the cadence.
• Scope: management, information, domains, system, protection, review, capability, systems.

Evidence to collect

• Policy Document. A signed and version-controlled policy / standard / procedure document.

Signed policy or standard documents the safeguard. Focus: Test Covert Channels For Exploitability.

Common pitfalls

• Policies that no engineer has read; the version in Confluence drifts from the version that's actually being enforced.

How it maps to other frameworks

Computed from shared tags, control component and key-operation subjects — handy when you are reconciling controls across an audit.

• NIST SP 800-171 Rev. 3 3.14.3 — Security Alerts, Advisories, and Directives
• HIPAA (45 CFR Part 164) 164.308(a)(1)(ii)(D) — Security Management Process -Information System Activity Review
• ISO/IEC 27001:2022 A.5.1 — Policies for information security
• BSI C5:2020 SP-01 — Documentation, communication and provision of policies and instructions

Related controls in NIST SP 800-53 Rev. 5

• Control SC-46 — Cross Domain Policy Enforcement
• Control CP-4(5) — Self-Challenge
• Control SC-7(20) — Dynamic Isolation And Segregation
• Control SC-39 — Process Isolation
• Control PE-19 — Information Leakage
• Control SC-16(1) — Integrity Verification

References

• NIST Computer Security Resource Center — NIST SP 800-53 Rev. 5
• Catalogue identifier: Control SC-31(1)

Topics: governance riskcode review testingpolicy management