SA 8(2) Least Common Mechanism

---
name: "SA-8(2)_least-common-mechanism"
description: "Implement the security design principle of least common mechanism in [organization-defined]."
category: "configuration"
version: "5.2.0"
author: "cyberstrike-official"
tags:
  - nist
  - sp800-53
  - rev5
  - sa-8-2
  - sa
  - enhancement
tech_stack:
  - any
cwe_ids:
  - CWE-16
chains_with: []
prerequisites:
  - SA-8
severity_boost: {}
---

# SA-8(2) Least Common Mechanism

> **Enhancement of:** SA-8

## High-Level Description

**Family:** System and Services Acquisition (SA)
**Framework:** NIST SP 800-53 Rev 5

The principle of least common mechanism states that the amount of mechanism common to more than one user and depended on by all users is minimized [POPEK74](#79453f84-26a4-4995-8257-d32d37aefea3) . Mechanism minimization implies that different components of a system refrain from using the same mechanism to access a system resource. Every shared mechanism (especially a mechanism involving shared variables) represents a potential information path between users and is designed with care to ensure that it does not unintentionally compromise security [SALTZER75](#c9495d6e-ef64-4090-8509-e58c3b9009ff) . Implementing the principle of least common mechanism helps to reduce the adverse consequences of sharing the system state among different programs. A single program that corrupts a shared state (including shared variables) has the potential to corrupt other programs that are dependent on the state. The principle of least common mechanism also supports the principle of simplicity of design and addresses the issue of covert storage channels [LAMPSON73](#d1cdab13-4218-400d-91a9-c3818dfa5ec8).

## What to Check

- [ ] Verify SA-8(2) Least Common Mechanism is documented in SSP
- [ ] Confirm control is operating effectively
- [ ] Review evidence of continuous monitoring for SA-8(2)
- [ ] Verify enhancement builds upon base control SA-8

## How to Test

### Step 1: Review Documentation

Examine the System Security Plan (SSP) and related artifacts for SA-8(2) 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 |
| ------------- | --------------------------------- | ----- |
| Manual Review | Documentation and interview-based | N/A   |

## Remediation Guide

### Control Statement

Implement the security design principle of least common mechanism in [organization-defined].

### Implementation Guidance

The principle of least common mechanism states that the amount of mechanism common to more than one user and depended on by all users is minimized [POPEK74](#79453f84-26a4-4995-8257-d32d37aefea3) . Mechanism minimization implies that different components of a system refrain from using the same mechanism to access a system resource. Every shared mechanism (especially a mechanism involving shared variables) represents a potential information path between users and is designed with care to ensure that it does not unintentionally compromise security [SALTZER75](#c9495d6e-ef64-4090-8509-e58c3b9009ff) . Implementing the principle of least common mechanism helps to reduce the adverse consequences of sharing the system state among different programs. A single program that corrupts a shared state (including shared variables) has the potential to corrupt other programs that are dependent on the state. The principle of least common mechanism also supports the principle of simplicity of design and addresses the issue of covert storage channels [LAMPSON73](#d1cdab13-4218-400d-91a9-c3818dfa5ec8).

## Risk Assessment

| Finding                                        | Severity | Impact                                     |
| ---------------------------------------------- | -------- | ------------------------------------------ |
| SA-8(2) Least Common Mechanism not implemented | Medium   | System and Services Acquisition            |
| SA-8(2) partially implemented                  | Low      | Incomplete System and Services Acquisition |

## CWE Categories

| CWE ID | Title         |
| ------ | ------------- |
| CWE-16 | Configuration |

## References

- [NIST SP 800-53 Rev 5 - SA-8(2)](https://csrc.nist.gov/projects/cprt/catalog#/cprt/framework/version/SP_800_53_5_1_1/home?element=sa-8.2)
- [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 (none) reviewed