AC 20(1) Limits On Authorized Use

---
name: "AC-20(1)_limits-on-authorized-use"
description: "Permit authorized individuals to use an external system to access the system or to process, store, or transmit organization-controlled information onl"
category: "authorization"
version: "5.2.0"
author: "cyberstrike-official"
tags:
  - nist
  - sp800-53
  - rev5
  - ac-20-1
  - ac
  - enhancement
tech_stack:
  - aws
  - azure
  - gcp
  - linux
  - windows
cwe_ids:
  - CWE-284
chains_with:
  - CA-2
prerequisites:
  - AC-20
severity_boost:
  CA-2: "Chain with CA-2 for comprehensive security coverage"
---

# AC-20(1) Limits on Authorized Use

> **Enhancement of:** AC-20

## High-Level Description

**Family:** Access Control (AC)
**Framework:** NIST SP 800-53 Rev 5

Limiting authorized use recognizes circumstances where individuals using external systems may need to access organizational systems. Organizations need assurance that the external systems contain the necessary controls so as not to compromise, damage, or otherwise harm organizational systems. Verification that the required controls have been implemented can be achieved by external, independent assessments, attestations, or other means, depending on the confidence level required by organizations.

## What to Check

- [ ] Verify AC-20(1) Limits on Authorized Use is documented in SSP
- [ ] Validate all 2 control requirements are implemented
- [ ] Confirm control is operating effectively
- [ ] Review evidence of continuous monitoring for AC-20(1)
- [ ] Verify enhancement builds upon base control AC-20

## How to Test

### Step 1: Review Documentation

Examine the System Security Plan (SSP) and related artifacts for AC-20(1) implementation details. Verify the organization has documented how this control is satisfied.

### Step 2: Validate Implementation

```
# For cloud environments, use cloud-audit-mcp tools
# For on-premises, review system configurations directly

# Example: Check if account management policies exist
grep -r "account.management\|access.control" /etc/security/ 2>/dev/null
```

### Step 3: Test Operating Effectiveness

Verify the control is actively functioning, not just documented. Check logs, configurations, and operational evidence.

## Tools

| Tool            | Purpose                                | Usage                      |
| --------------- | -------------------------------------- | -------------------------- |
| cloud-audit-mcp | Check IAM policies and access controls | `cloud_audit_iam_policies` |
| hackbrowser | Test web application access controls   | `hackbrowser`        |

## Remediation Guide

### Control Statement

Permit authorized individuals to use an external system to access the system or to process, store, or transmit organization-controlled information only after:
Verification of the implementation of controls on the external system as specified in the organization’s security and privacy policies and security and privacy plans; or
Retention of approved system connection or processing agreements with the organizational entity hosting the external system.

### Implementation Guidance

Limiting authorized use recognizes circumstances where individuals using external systems may need to access organizational systems. Organizations need assurance that the external systems contain the necessary controls so as not to compromise, damage, or otherwise harm organizational systems. Verification that the required controls have been implemented can be achieved by external, independent assessments, attestations, or other means, depending on the confidence level required by organizations.

## Risk Assessment

| Finding                                           | Severity | Impact                    |
| ------------------------------------------------- | -------- | ------------------------- |
| AC-20(1) Limits on Authorized Use not implemented | High     | Access Control            |
| AC-20(1) partially implemented                    | Medium   | Incomplete Access Control |

## CWE Categories

| CWE ID  | Title                   |
| ------- | ----------------------- |
| CWE-284 | Improper Access Control |

## References

- [NIST SP 800-53 Rev 5 - AC-20(1)](https://csrc.nist.gov/projects/cprt/catalog#/cprt/framework/version/SP_800_53_5_1_1/home?element=ac-20.1)
- [NIST SP 800-53A Rev 5 (Assessment Procedures)](https://csrc.nist.gov/pubs/sp/800/53/a/r5/final)
- [NIST SP 800-53 Rev 5 Full Catalog](https://csrc.nist.gov/pubs/sp/800/53/r5/upd1/final)

## Checklist

- [ ] Control documented in SSP
- [ ] Implementation evidence collected
- [ ] Operating effectiveness validated
- [ ] Continuous monitoring in place
- [ ] Related controls (CA-2) reviewed