NIST SP 800-53 Rev. 5 AT-2(4) — Suspicious Communications And Anomalous System Behavior

What this control requires

Provides literacy training to recognize suspicious communications and anomalous system behavior, using defined indicators of malicious code, to enhance early detection and response. This control supports the Security Awareness Training System capability within the Awareness and Training family.

In plain English

Provides literacy training to recognize suspicious communications and anomalous system behavior, using defined indicators of malicious code, to enhance early detection and response. In practice, this means you can prove you security system-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.

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 Awareness and Training, the assessor will trace your implementation back to the catalogue reference (Control AT-2(4)) and look for objective evidence on the latest two assessment cycles.

How to implement

Secure Development

Pipeline. Require code review, SAST (Semgrep / Snyk Code), SCA (Dependabot / Renovate), secret-scanning and IaC scanning in the merge pipeline.

Branch protection. Protected branches enforce reviews, signed commits and passing CI before merge; document the protection rules as the control evidence.

Code Review Testing

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

Operational checklist

• Security. Document the trigger, the owner and the cadence.
• Detection. Document the trigger, the owner and the cadence.
• Review. Document the trigger, the owner and the cadence.
• Literacy. Document the trigger, the owner and the cadence.
• Suspicious. Document the trigger, the owner and the cadence.
• Scope: system, application, review, capability, behavior, malicious code, response, security.

Evidence to collect

• Code Repo Scan. Source-control evidence — branch protection, required reviewers, CI status, SCA / SAST reports.

Source control pipelines (GitHub, GitLab) enforce SDLC guardrails. Focus: Suspicious Communications And Anomalous System Behavior.

Common pitfalls

• CI security checks set to warn-only; the merge button is faster than the security feedback.

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 3.14.2 — Malicious Code Protection
• CIS Controls v8 16.12 — Implement Code-Level Security Checks
• ISO/IEC 27001:2022 A.8.28 — Secure coding

Related controls in NIST SP 800-53 Rev. 5

• Control AT-2(3) — Social Engineering And Mining
• Control CP-3(1) — Simulated Events
• Control MA-3 — Maintenance Tools
• Control SC-7(9) — Restrict Threatening Outgoing Communications Traffic
• Control SC-35 — External Malicious Code Identification
• Control SC-3(3) — Minimize Nonsecurity Functionality

References

• NIST Computer Security Resource Center — NIST SP 800-53 Rev. 5
• Catalogue identifier: Control AT-2(4)

Topics: application securityawareness trainingsecure developmentcode review testingdevsecopssecurity training