# NIST SP 800-53 Rev. 5 SC-39(2) — Separate Execution Domain Per Thread - Source: https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/sc-39-2-separate-execution-domain-per-thread - Section: [Compliance](https://support.icompaas.com/compliance) › [NIST SP 800-53 Rev. 5 Controls](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5) › SC — System and Communications Protection - Last updated: 2026-06-05 - Publisher: iCompaas, Inc. (https://www.icompaas.com) **NIST SP 800-53 Rev. 5**·Control `SC-39(2)`·high·Component: **System and Communications Protection** ## What this control requires > Maintain a separate execution domain for each thread in organization-defined multi-threaded processing. This ensures that each thread operates in its own address space, preventing unauthorized access or modification by other threads, thus enhancing security and stability in multi-threaded environments. This control supports the Thread Execution Isolation capability within the System and Communications Protection family. > > — NIST SP 800-53 Rev. 5, Control SC-39(2) ### In plain English Maintain a separate execution domain for each thread in organization-defined multi-threaded processing. 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-39(2)) and look for objective evidence on the latest two assessment cycles. ## How to implement #### 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. - **Access.** Document the trigger, the owner and the cadence. - **Security.** Document the trigger, the owner and the cadence. - **Domain.** Document the trigger, the owner and the cadence. - **Separate.** Document the trigger, the owner and the cadence. - **Scope:** management, organization, system, protection, environments, capability, policy, security. ## Evidence to collect - **Policy Document.** A signed and version-controlled policy / standard / procedure document. Signed policy or standard documents the safeguard. Focus: Separate Execution Domain Per Thread. ## 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](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3/3-14-3-security-alerts-advisories-and-directives) - [**HIPAA (45 CFR Part 164) 164.308(a)(5)(i)** — Security Awareness and Training](https://support.icompaas.com/compliance/hipaa/164-308-a-5-i-security-awareness-and-training) - [**BSI C5:2020 SP-01** — Documentation, communication and provision of policies and instructions](https://support.icompaas.com/compliance/bsi-c5-2020/sp-01-documentation-communication-and-provision-of-policies-and-instructions) - [**ISO/IEC 27001:2022 A.5.1** — Policies for information security](https://support.icompaas.com/compliance/iso-27001-2022/a-5-1-policies-for-information-security) ## Related controls in NIST SP 800-53 Rev. 5 - [**Control SC-15(4)** — Explicitly Indicate Current Participants](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/sc-15-4-explicitly-indicate-current-participants) - [**Control SC-7(20)** — Dynamic Isolation And Segregation](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/sc-7-20-dynamic-isolation-and-segregation) - [**Control SC-16(2)** — Anti-Spoofing Mechanisms](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/sc-16-2-anti-spoofing-mechanisms) - [**Control SC-23(3)** — Unique System-Generated Session Identifiers](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/sc-23-3-unique-system-generated-session-identifiers) - [**Control SC-3(5)** — Layered Structures](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/sc-3-5-layered-structures) - [**Control SC-46** — Cross Domain Policy Enforcement](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/sc-46-cross-domain-policy-enforcement) ## References - [NIST Computer Security Resource Center — NIST SP 800-53 Rev. 5](https://csrc.nist.gov/Projects/risk-management/sp800-53-controls) - Catalogue identifier: `Control SC-39(2)` Topics: governance riskpolicy management ## Related compliance guidance - [NIST SP 800-53 Rev. 5: a practical implementation guide for cloud teams](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5): Start with the full NIST SP 800-53 implementation guide — scope, roadmap, evidence and how the assessment runs. - [NIST SP 800-171 and CMMC: a practical guide to protecting CUI in the cloud](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3): If your obligation is protecting CUI in your own systems for a federal or defence contract, this derived subset — not the full catalogue — is the requirement. - [SOC 2 compliance: a practical implementation guide for cloud-native SaaS teams](https://support.icompaas.com/compliance/soc-2-trust-services-criteria): Most commercial SaaS already hold a SOC 2 Type 2, and FedRAMP 20x Class A is designed for providers that have one.