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

DevOps & Security

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

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/NIST/SP800-53_rev5/SC_system-and-communications-protection/SC-7(5)_deny-by-default-allow-by-exception/SKILL.md

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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

Tool	Purpose	Usage
cloud-audit-mcp	Check encryption and network controls	`cloud_audit_encryption`
nmap	Network scanning	`nmap -sV --script ssl-enum-ciphers`

Remediation Guide

Control Statement

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

Implementation Guidance

Risk Assessment

Finding	Severity	Impact
SC-7(5) Deny by Default — Allow by Exception not implemented	High	System and Communications Protection
SC-7(5) partially implemented	Medium	Incomplete System and Communications Protection

CWE Categories

CWE ID	Title
CWE-311	Missing Encryption of Sensitive Data

References

Checklist

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