Network security controls

The PCI DSS 4.0 network security controls requirement means you must protect the cardholder data environment (CDE) by using segmented and actively managed network controls so only authorized traffic can reach CDE systems. Operationalize it by defining the CDE boundary, enforcing deny-by-default network rules, validating segmentation, and keeping audit-ready evidence of configurations and reviews ¹.

Key takeaways:

• Define and document the CDE boundary and all network paths into it; everything else depends on this ¹.
• Enforce segmentation with managed network controls (for example, firewalls and rule sets) and review those rules on a schedule you can prove ¹.
• Keep evidence that controls work in practice: configs, diagrams, review records, and segmentation validation results ¹.

“Network security controls” under PCI DSS 4.0 is a requirement you pass or fail on operational reality, not policy language. Assessors will look for a clearly defined cardholder data environment (CDE), explicit network boundaries, and managed controls that restrict connectivity into (and often within) the CDE. They will also test whether segmentation claims are real by examining rules, traffic paths, and proof that controls are maintained over time ¹.

For a Compliance Officer, CCO, or GRC lead, the fastest path is to translate the requirement into three workstreams you can drive: (1) scope and boundaries (what is the CDE and what is not), (2) control enforcement (what blocks/permits traffic and how it is managed), and (3) evidence (what artifacts prove design and ongoing operation). If you can’t show those three clearly, you’ll spend the assessment arguing about scope and intent instead of demonstrating control performance.

This page gives requirement-level implementation guidance you can hand to Network/Security Engineering, track in a GRC system, and defend during a PCI DSS 4.0 assessment ¹.

Regulatory text

Regulatory excerpt (PCI DSS 4.0): “Protect cardholder data environment through segmented and managed network controls.” ¹

What the operator must do

• Protect the CDE by controlling network connectivity so only authorized traffic can reach systems that store, process, or transmit cardholder data ¹.
• Use segmentation intentionally to separate the CDE from other networks, reducing exposure and (where appropriate) limiting PCI scope, but only if segmentation is demonstrably effective ¹.
• Manage network controls over time: configuration changes, rule approvals, and periodic reviews must be governed and evidenced, not left to ad hoc engineering practice ¹.

Plain-English interpretation (what this means in practice)

You need a network design where the CDE is a clearly bounded zone and access into it is tightly controlled. “Managed network controls” generally means you have devices and configurations (for example, firewalls, security groups, ACLs, and routing controls) that enforce what can talk to the CDE, from where, on which ports/protocols, and for what business reason. “Segmented” means the CDE isn’t casually reachable from corporate networks, third-party connections, or the public internet without explicit, documented, and reviewed access paths ¹.

A common operational translation:

• Deny by default into the CDE.
• Permit by exception with a documented business justification.
• Prove it with configs, diagrams, and validation results ¹.

Who it applies to

Entity types: Merchants and service providers that are in scope for PCI DSS 4.0 ¹.

Operational context where this shows up

• Any environment that contains the CDE: on-prem, cloud, hybrid, colocation, and hosted service provider networks ¹.
• Third-party connectivity that can touch the CDE (for example, managed service providers, payment processors’ support access, or upstream network providers). Treat these as “third party” connections that must be controlled and evidenced ¹.
• Modern patterns that often break segmentation: shared services (DNS, logging, patching), flat internal networks, broad “any/any” firewall rules, overly permissive cloud security groups, and “temporary” exceptions that never expire.

What you actually need to do (step-by-step)

Step 1: Define and freeze the CDE boundary (scope is a control)

1. Inventory CDE assets and dependencies. Identify systems that store/process/transmit cardholder data and the supporting components that connect to them ¹.
2. Draw the network boundary. Produce a current network diagram that shows:
   • CDE segments
   • inbound and outbound paths
   • trust boundaries (internet, corporate, third party links)
   • security enforcement points (firewalls, gateways, cloud security controls) ¹.
3. Document “in-scope by connectivity” components. If something can connect to the CDE, it becomes part of the assessment conversation. Make those connections explicit and justified ¹.

Operator tip: Most audit friction comes from undocumented paths (VPNs, peering, admin networks, shared tooling). Surface them early.

Step 2: Implement segmented, managed controls at every ingress/egress

1. Set a baseline network policy for CDE access. For each allowed flow, document: source, destination, port/protocol, direction, purpose, and owner ¹.
2. Enforce deny-by-default. Configure network controls so traffic into the CDE is blocked unless explicitly allowed. Avoid broad rules that effectively bypass segmentation ¹.
3. Control administrative access paths. Management access (jump hosts, bastions, admin VPNs) should be constrained, logged, and separated from general user networks ¹.
4. Constrain third-party connectivity. Treat every third-party route into the CDE as high scrutiny:
   • limit source IP ranges
   • restrict to required services/ports
   • require time-bound access where feasible
   • log and review access ¹.

Step 3: Put rule management under change control (and make it provable)

1. Establish rule standards. Require rule naming, ticket/approval references, business justification, owner, and expiry/recertification date fields in your firewall/security group process.
2. Run periodic rule reviews. The requirement expects that rules are reviewed “regularly” ¹. Pick a cadence you can sustain, then keep evidence of each review, outcomes, and remediation.
3. Track exceptions explicitly. Temporary openings are where segmentation fails. Require documented approvals and closures backed by evidence (ticket closure, rule removal, updated diagram where relevant).

Daydream fit (practical): Use Daydream to assign control ownership (network engineering for enforcement, security for validation, GRC for evidence), track rule review tasks, and store artifacts in a single evidence set aligned to the network security controls requirement ¹.

Step 4: Validate segmentation (don’t rely on “we think it’s isolated”)

1. Test connectivity paths. Demonstrate that non-CDE networks cannot reach CDE systems except through documented, controlled paths ¹.
2. Validate after material changes. Any significant network change can invalidate segmentation claims. Tie segmentation validation to network change management triggers ¹.
3. Record results in an assessor-friendly format. Capture test scope, method, date, tester, findings, and remediation actions.

Step 5: Operational monitoring you can defend

1. Log security control changes. Keep change events for firewalls, routers, cloud security controls, and remote access gateways ¹.
2. Monitor for policy drift. Implement alerting or scheduled checks for overly permissive rules and new paths into the CDE.
3. Reconcile diagrams and reality. Update diagrams when rules or topology changes. Stale diagrams are a recurring audit hangup.

Required evidence and artifacts to retain (audit-ready checklist)

Maintain an evidence packet that maps cleanly to “segmented and managed network controls” ¹:

Evidence artifact	What it proves	Owner
Current network diagram(s) with CDE boundary	Defined scope and segmentation design	Network/Security Architecture
Data flow diagram for cardholder data (if maintained)	How CHD traverses systems and networks	App/Platform + Security
Firewall/security group/ACL configurations (export/snapshots)	Controls exist and are configured as claimed	Network/SecOps
Rule review records (dated, signed/approved)	Controls are managed over time	Network + Security + GRC
Change tickets and approvals for rule changes	Governance and authorization	Change Management
Segmentation validation test plan + results	Segmentation is effective	Security Testing/Network
Third-party access documentation (allowed paths, approvals, logs)	External connectivity is controlled	Security + Vendor/TPRM
Exceptions register and closure evidence	Deviations are tracked and remediated	GRC

Common exam/audit questions and hangups (what assessors press on)

• “Show me the CDE boundary and every inbound path.” If you can’t enumerate paths, assessors assume unknown connectivity risk ¹.
• “Why is this rule here?” Rules without business justification and ownership often fail review expectations ¹.
• “Prove segmentation works.” Claims of isolation need validation results, not only architecture diagrams ¹.
• “How do you keep rules clean over time?” They will look for periodic reviews and change control integration ¹.
• “What about cloud?” Expect scrutiny on security groups, network ACLs, routing, peering, and identity-based access paths that effectively bypass network segmentation ¹.

Frequent implementation mistakes (and how to avoid them)

1. Mistake: Defining the CDE too narrowly to reduce scope.
   Avoidance: Start from real data flows and connectivity. If a system can reach the CDE, document the path and either segment it out or bring it into scope intentionally ¹.

2. Mistake: Overly permissive “temporary” rules that become permanent.
   Avoidance: Require expiry dates and a monthly exceptions review owned by Security/GRC, with engineering accountable for closure ¹.

3. Mistake: Diagrams that don’t match production.
   Avoidance: Treat diagrams as controlled documents updated through the same change process as network modifications ¹.

4. Mistake: Assuming a VPN equals segmentation.
   Avoidance: VPN is only a transport. Segmentation depends on what the VPN can reach after authentication and what network controls enforce ¹.

5. Mistake: No clear rule ownership.
   Avoidance: Assign an application or service owner for each allowed flow. Remove rules with no owner after review and stakeholder notice.

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this requirement, so this page does not cite enforcement outcomes.

Practically, weak network security controls increase the chance that a compromise in a non-CDE system can laterally move into CDE assets. In PCI assessments, the immediate risk is a failed or delayed assessment due to inability to prove effective segmentation and ongoing management of network controls ¹.

Practical 30/60/90-day execution plan

Days 0–30: Get to a defensible baseline

• Confirm the in-scope entity/entities and environments for PCI DSS ¹.
• Inventory CDE assets and map cardholder data connectivity at a high level ¹.
• Produce a current CDE network diagram with enforcement points ¹.
• Export current firewall/security group rule sets for CDE boundaries.
• Stand up an evidence folder structure in Daydream (or your GRC system) keyed to diagrams, configs, reviews, and validation results ¹.

Days 31–60: Fix the highest-risk gaps and formalize governance

• Implement deny-by-default at CDE boundaries where feasible; document justified exceptions ¹.
• Create a rule review procedure and ownership model; run the first review and capture decisions ¹.
• Establish third-party connectivity register for any paths into the CDE ¹.
• Tie network rule changes to change management approvals; require ticket references in rule metadata.

Days 61–90: Prove effectiveness and make it repeatable

• Run segmentation validation testing and document results and remediation ¹.
• Reconcile diagrams to production after changes; publish controlled versions.
• Operationalize recurring reviews (rules, exceptions, third-party access paths) with tracked tasks and evidence capture in Daydream ¹.
• Prepare an assessor-ready narrative: “Here is our CDE boundary, here are allowed flows, here is how we approve and review them, and here is the segmentation validation proof” ¹.

Frequently Asked Questions

Does using cloud security groups count as “managed network controls”?

Yes, if they enforce the CDE boundary and you manage them through approvals, periodic reviews, and evidence of changes. Assessors will still expect you to prove segmentation effectiveness and governance over time ¹.

Can segmentation reduce PCI scope automatically?

Segmentation can reduce which systems are in scope only if it is effective and demonstrable. If connectivity exists (even unintentionally), those connected systems can become in-scope in practice ¹.

What evidence is most likely to be requested during a PCI assessment?

Expect current network diagrams showing the CDE boundary, exports of relevant rule sets, proof of rule reviews, and segmentation validation results. Keep change tickets and approvals ready for sampled rule changes ¹.

How do we handle third-party access into the CDE?

Document each third-party connection path, restrict it to required sources and services, and keep approvals and access logs. Treat third-party paths as high-risk and review them on the same cadence as other CDE boundary rules ¹.

Our network team says rules are “reviewed in the tool.” Is that enough?

Only if you can produce dated records that show what was reviewed, who approved it, what changed, and why. A verbal process or an informal note usually fails under sampling ¹.

What’s the fastest way to get audit-ready if we’re behind?

Start by defining the CDE boundary and collecting current configs and diagrams, then run a structured rule review focused on inbound access to the CDE. Use Daydream to assign owners, schedule reviews, and centralize evidence so you can answer assessor requests without scrambling ¹.

Related compliance topics

• 2025 SEC Marketing Rule Examination Focus Areas
• Access and identity controls
• Access Control (AC)
• Access control and identity discipline
• Access control management

Footnotes

1. PCI DSS v4.0