SC-7(5)_deny-by-default-allow-by-exception

SC-7(5) Deny by Default — Allow by Exception

Enhancement of: SC-7

High-Level Description

Family: System and Communications Protection (SC) Framework: NIST SP 800-53 Rev 5

Denying by default and allowing by exception applies to inbound and outbound network communications traffic. A deny-all, permit-by-exception network communications traffic policy ensures that only those system connections that are essential and approved are allowed. Deny by default, allow by exception also applies to a system that is connected to an external system.

What to Check

• Verify SC-7(5) Deny by Default — Allow by Exception is documented in SSP
• Confirm control is operating effectively
• Review evidence of continuous monitoring for SC-7(5)
• Verify enhancement builds upon base control SC-7

How to Test

Step 1: Review Documentation

Examine the System Security Plan (SSP) and related artifacts for SC-7(5) 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

Remediation Guide

Control Statement

Deny network communications traffic by default and allow network communications traffic by exception [organization-defined].

Implementation Guidance

Denying by default and allowing by exception applies to inbound and outbound network communications traffic. A deny-all, permit-by-exception network communications traffic policy ensures that only those system connections that are essential and approved are allowed. Deny by default, allow by exception also applies to a system that is connected to an external system.

Risk Assessment

CWE Categories

References

• NIST SP 800-53 Rev 5 - SC-7(5)
• NIST SP 800-53A Rev 5 (Assessment Procedures)
• NIST SP 800-53 Rev 5 Full Catalog

Checklist

• Control documented in SSP
• Implementation evidence collected
• Operating effectiveness validated
• Continuous monitoring in place
• Related controls (none) reviewed