# NIST SP 800-53 Rev. 5 AC-25 — Reference Monitor - Source: https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/ac-25-reference-monitor - 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) › AC — Access Control - Last updated: 2026-06-05 - Publisher: iCompaas, Inc. (https://www.icompaas.com) **NIST SP 800-53 Rev. 5**·Control `AC-25`·critical·Component: **Access Control** ## What this control requires > Implements a tamperproof, always-invoked, and verifiable reference monitor for access control policies, ensuring secure subject-object interactions. This control supports the Reference Validation Mechanism capability within the Access Control family. > > — NIST SP 800-53 Rev. 5, Control AC-25 ### In plain English Implements a tamperproof, always-invoked, and verifiable reference monitor for access control policies, ensuring secure subject-object interactions. In practice, this means you can prove you access 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 **critical** in the source catalogue. Treat gaps here as production incidents in the risk register, not housekeeping. ## 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 **Access Control**, the assessor will trace your implementation back to the catalogue reference (Control AC-25) and look for objective evidence on the latest two assessment cycles. ## How to implement #### Logging Monitoring **AWS.** Org-trail CloudTrail to a central log archive account, GuardDuty in every region, and Security Hub for cross-source correlation. **Azure.** Pipe every diagnostic setting into a central Log Analytics workspace; onboard Microsoft Sentinel for SIEM/SOAR. **GCP.** Aggregate audit logs in a dedicated logging project with sink to BigQuery; enable Security Command Center Premium and route findings to Chronicle SIEM. ### Operational checklist - **Access.** Document the trigger, the owner and the cadence. - **Object.** Document the trigger, the owner and the cadence. - **Validation.** Document the trigger, the owner and the cadence. - **Review.** Document the trigger, the owner and the cadence. - **Access Control.** Document the trigger, the owner and the cadence. - **Scope:** management, access control, identity, monitor, review, capability, secure, interactions. ## Evidence to collect - **Identity Scan.** IAM / IdP exports — Entra ID, Okta, IAM Identity Center, Workspace directory — showing accounts, roles, MFA state and last sign-in. Identity analytics (Okta, SailPoint, Access Analyzer) demonstrates least-privilege. Focus: Reference Monitor. ## Common pitfalls - Per-account logging that nobody stitches together at the org level — incidents that cross accounts go undetected for days. ## 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. - [**CIS Controls v8 6.7** — Centralize Access Control](https://support.icompaas.com/compliance/cis-controls-v8/6-7-centralize-access-control) - [**NIST SP 800-171 Rev. 3 3.1.4** — Separation of Duties](https://support.icompaas.com/compliance/nist-sp-800-171-rev-3/3-1-4-separation-of-duties) - [**BSI C5:2020 PS-04** — Physical site access control](https://support.icompaas.com/compliance/bsi-c5-2020/ps-04-physical-site-access-control) - [**ISO/IEC 27001:2022 A.8.2** — Privileged access rights](https://support.icompaas.com/compliance/iso-27001-2022/a-8-2-privileged-access-rights) - [**SOC 2 (2017 TSC) CC6.1** — Logical Access Controls](https://support.icompaas.com/compliance/soc-2-trust-services-criteria/cc6-1-logical-access-controls) ## Related controls in NIST SP 800-53 Rev. 5 - [**Control AC-2(4)** — Automated Audit Actions](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/ac-2-4-automated-audit-actions) - [**Control AC-6(6)** — Privileged Access By Non-Organizational Users](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/ac-6-6-privileged-access-by-non-organizational-users) - [**Control AC-10** — Concurrent Session Control](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/ac-10-concurrent-session-control) - [**Control AC-18(1)** — Authentication And Encryption](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/ac-18-1-authentication-and-encryption) - [**Control AC-5** — Separation Of Duties](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/ac-5-separation-of-duties) - [**Control AC-24(1)** — Transmit Access Authorization Information](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/ac-24-1-transmit-access-authorization-information) ## 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 AC-25` Topics: identity accessidentity managementaccess reviewprivileged accesslogging monitoring ## 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.