DNS Security

HICP Practice 5.6 requires you to secure DNS by (1) blocking known-bad and risky domain lookups (DNS filtering), (2) validating DNS response integrity where feasible (DNSSEC), and (3) monitoring for DNS-based threats and data exfiltration (including DNS tunneling). Operationalize it by centralizing DNS resolution, enforcing policy at the resolver, and retaining logs plus investigation records. ¹

Key takeaways:

• Put DNS control in one place: managed resolvers + mandatory forwarding from endpoints and networks.
• Treat DNS logs as a primary detection source for malware callbacks and exfiltration attempts.
• DNSSEC is not “turn it on once”; you need a scope decision, validation controls, and break-glass procedures. ¹

DNS is a control plane for almost every security outcome you care about: phishing prevention, malware command-and-control disruption, and visibility into suspicious outbound behavior. HICP Practice 5.6 makes DNS a defined security requirement: implement DNS filtering, DNSSEC, and monitoring for DNS-based threats and data exfiltration. ¹

For a CCO or GRC lead, the fastest path is to translate “DNS security” into three auditable capabilities: (1) a documented DNS policy enforced by a controlled resolver path, (2) technical configuration evidence that the organization blocks malicious and inappropriate destinations at DNS time, and (3) detective controls that identify DNS tunneling and other anomalous query patterns, with response playbooks and tickets to prove you acted.

This page is written to help you operationalize the requirement without getting stuck in network-architecture debates. You’ll get a step-by-step implementation path, a concrete evidence list for audits, common examiner questions, and a practical execution plan that aligns Security, IT, and compliance workstreams to the same deliverables. ¹

Regulatory text

HICP Practice 5.6 (DNS Security): “Implement DNS security measures including DNS filtering, DNSSEC, and monitoring for DNS-based threats and data exfiltration.” ¹

Operator interpretation (what you must be able to show):

1. DNS filtering exists and is enforced: you block resolution of domains associated with malware, phishing, and other policy-prohibited categories, and you can show where the policy lives and how it’s applied. ¹
2. DNSSEC is addressed, not ignored: you have a defined approach to DNSSEC (validation at resolvers where feasible; documented exceptions where not), plus operational procedures for failures/misconfigurations. ¹
3. DNS monitoring detects threats and exfiltration: you collect DNS telemetry, alert on suspicious patterns (including tunneling/exfiltration), and demonstrate incident handling through tickets and post-incident notes. ¹

Plain-English requirement (what “good” looks like)

You control how users, servers, and workloads turn names into IP addresses. That control blocks known bad destinations before connections occur, validates DNS answers to reduce tampering risk, and gives your detection team visibility into abnormal outbound behavior that can indicate compromise or data theft. ¹

Who it applies to

Entity types

• Healthcare organizations (providers, payers, labs, etc.) operating enterprise networks, clinical networks, remote workforce, and hybrid/cloud environments. ¹
• Health IT vendors that host, integrate, or support systems used to create, receive, maintain, or transmit healthcare data, or that provide networked products/services into healthcare environments. ¹

Operational contexts where auditors focus

• End-user endpoints (managed devices, VDI, remote access)
• Server and identity infrastructure (AD/DNS, domain controllers, critical apps)
• Cloud workloads (IaaS/PaaS, container platforms) and SaaS egress
• Guest/IoT/medical device networks that may bypass standard endpoint controls
• Third-party connections (MSPs, billing partners, EDI interfaces) where DNS paths can be ambiguous

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

1) Decide and document your DNS security control model

Create a one-page “DNS Security Standard” that answers:

• Authoritative vs. recursive: which systems provide recursive resolution for corporate assets.
• Central resolvers: the approved resolvers (on-prem, cloud, or provider-managed).
• Allowed DNS transports: whether you permit DoH/DoT from endpoints or force all DNS to approved resolvers.
• Logging: what you log, where it’s stored, and who can access it.
• Exceptions: who can approve bypasses (and how they expire).
  This is the policy anchor for HICP 5.6 evidence. ¹

2) Centralize DNS resolution (so filtering and monitoring are real)

You cannot enforce DNS filtering or do reliable monitoring if endpoints can pick any resolver.

• Network controls: restrict outbound DNS (port 53/udp and 53/tcp) to approved resolvers; redirect or block everything else.
• Endpoint posture: manage DNS settings via MDM/GPO; prevent local resolver overrides where feasible.
• Remote users: ensure VPN or secure access tooling routes DNS to your approved resolvers, or use an endpoint DNS agent that enforces policy off-network.
• Cloud: define DNS egress paths for workloads (VPC/VNet resolvers, forwarders) and align them to the same filtering and logging approach. ¹

Exam hangup: If you allow direct-to-internet DoH, auditors will ask how you still “implement DNS filtering” centrally. Have a clear answer (block unmanaged DoH endpoints; allow only your sanctioned DoH to your resolver; or enforce filtering on the endpoint). ¹

3) Implement DNS filtering with a clear policy

Operational steps:

1. Pick policy categories that match your risk posture (malware, phishing, newly registered domains, parked domains, typo-squatting, command-and-control, dynamic DNS). Keep the list short and defensible.
2. Define block action (NXDOMAIN, sinkhole, redirect to block page) and align it to SOC workflows and user support needs.
3. Add allowlisting workflow with required fields: business justification, requestor, system owner, expiry date, validation step (confirm domain ownership), and approval.
4. Validate coverage across corporate, cloud, and remote contexts by testing representative clients and networks.
5. Operationalize reporting: review blocked-domain trends and top clients generating blocks; feed into threat hunting. ¹

4) Implement DNSSEC validation where feasible (and document the rest)

DNSSEC has two practical pieces: signing by zone owners (often external) and validation by your resolvers.

• Enable DNSSEC validation on your recursive resolvers if your platform supports it.
• Test failure modes: mis-signed zones happen. Define a break-glass process that requires ticketing, time-bounded exception, and post-event review.
• Document scope limits: some environments (legacy appliances, certain managed networks) may not support validation. Your job is to show an intentional risk decision, compensating controls, and a roadmap. ¹

5) Monitor DNS for threats and data exfiltration (detection + response)

To satisfy the “monitoring for DNS-based threats and data exfiltration” clause, you need both telemetry and action.

• Collect logs from recursive resolvers and filtering tools: query name, response code, client identifier (IP/device/user), timestamp, upstream resolver, policy action.
• Detection rules / alerts (examples you can implement and tune):
  • High NXDOMAIN rates by a single client (often DGA or misconfig)
  • Queries with very long subdomains or high-entropy labels (tunneling indicator)
  • Unusual query volume to a single domain, especially at steady intervals
  • Spikes in TXT record queries or large responses
  • New domains contacted by sensitive systems (domain controllers, EHR servers)
• Incident playbooks:
  • “Suspected DNS tunneling” triage steps (identify host, isolate, capture process tree, block domain, review egress logs)
  • “Malware callback blocked by DNS filter” response (endpoint scan, IOC sweep, user notification, containment)
• Integrate with SIEM/SOAR so DNS alerts generate tickets and measurable response actions. Retain the tickets; they are audit gold. ¹

6) Cover third parties and special networks explicitly

Common gaps show up in:

• Medical devices/IoT on segmented networks that use hardcoded DNS
• MSP-managed subnets that point to MSP resolvers
• SaaS apps that bypass your DNS controls via embedded resolvers or proxies
  Write requirements into third-party onboarding and network standards: “All organization-managed networks must use approved recursive resolvers and send DNS logs to central monitoring.” ¹

Required evidence and artifacts to retain (audit-ready)

Keep evidence mapped to the three HICP verbs: filtering, DNSSEC, monitoring. ¹

Governance

• DNS Security Standard / policy (owner, scope, exception process)
• Network diagrams showing resolver architecture and enforcement points
• Exception register for DNS bypass / allowlists (with approvals and expirations)

Technical configuration

• Resolver configuration exports/screenshots showing:
  • Forwarding settings and approved upstreams
  • DNSSEC validation settings (enabled/disabled) with rationale
  • Filtering categories/policies enabled and enforcement mode
• Firewall/proxy rules showing DNS egress restrictions (including handling of unauthorized DoH/DoT if applicable)
• Endpoint configuration evidence (MDM/GPO profiles, agent deployment reports)

Monitoring and response

• Sample DNS logs (sanitized) demonstrating collection fields
• SIEM alert rules or detection logic for tunneling/exfil indicators
• Incident tickets showing investigation, containment, and lessons learned
• Periodic review records (trend reports, tuning decisions)

How Daydream fits naturally Daydream helps GRC teams turn “DNS security requirement” into a control narrative with linked evidence: policy, resolver configs, log samples, and incident tickets in one place. The practical win is faster audits because the “DNS filtering / DNSSEC / monitoring” story stays consistent across IT, Security, and compliance.

Common exam/audit questions and hangups

• “Where is DNS filtering enforced?” Name the resolvers, enforcement points, and how remote users are covered. ¹
• “Can endpoints bypass DNS controls?” Be ready to discuss DoH/DoT posture and egress restrictions.
• “Show me DNSSEC.” Auditors will accept a scoped approach if you show configuration evidence or a documented exception with compensating controls. ¹
• “How do you detect DNS tunneling or exfiltration?” Show alert logic, examples of investigations, and outcomes. ¹
• “What about clinical/biomed networks and third parties?” Produce diagrams, segmentation decisions, and written requirements for those environments.

Frequent implementation mistakes (and how to avoid them)

1. Filtering without enforcement: A DNS filter subscription exists, but endpoints can still query public resolvers. Fix with egress controls and managed DNS settings.
2. DNS logs collected but not used: You store logs but have no detection content or tickets. Fix by implementing a small set of high-signal alerts and requiring documented triage.
3. DNSSEC treated as a checkbox: Validation is enabled but break-glass is undocumented, so operations disable it ad hoc during outages. Fix with a time-bounded exception workflow.
4. No allowance for legacy and medical devices: Hardcoded DNS breaks filtering rollouts. Fix with network-level interception where safe, or segment + monitor with compensating controls and a replacement plan. ¹

Enforcement context and risk implications

No public enforcement cases were provided in the supplied sources for this requirement. Practically, DNS is a high-frequency control surface: a weak DNS posture increases exposure to phishing, malware callbacks, and covert channels for outbound data movement. HICP 5.6 gives you a clear audit hook: if you cannot show filtering, DNSSEC decisions, and monitoring evidence, you will struggle to demonstrate “implemented DNS security measures.” ¹

Practical 30/60/90-day execution plan

First 30 days (stabilize and define)

• Assign control ownership (Network/Security) and compliance owner (GRC).
• Publish DNS Security Standard: resolver architecture, filtering policy baseline, logging requirements, exception process. ¹
• Inventory current resolvers, forwarders, and DNS logging coverage across on-prem, cloud, and remote access.

Next 60 days (enforce and instrument)

• Centralize recursive resolution for managed endpoints and key networks.
• Turn on DNS filtering categories aligned to your policy; create allowlist workflow with expirations.
• Enable DNSSEC validation where supported; document scoped exceptions and compensating controls. ¹
• Start shipping DNS logs to SIEM with consistent client identifiers.

Next 90 days (detect, respond, and prove it)

• Deploy DNS-based threat and tunneling detection rules; tune based on false positives.
• Run at least one tabletop for “suspected DNS tunneling/data exfiltration” and capture outputs as evidence.
• Produce an audit pack: policy, diagrams, config exports, sample logs, alert screenshots, and completed incident tickets mapped to HICP 5.6 language. ¹

Frequently Asked Questions

Do we have to implement all three: DNS filtering, DNSSEC, and monitoring?

HICP Practice 5.6 explicitly names all three measures. If DNSSEC validation is not feasible in parts of your environment, document the scope limitation, the decision owner, and compensating controls, then track a roadmap. ¹

Does a secure web gateway replace DNS filtering?

A web gateway helps, but it does not satisfy “DNS filtering” if DNS queries can still resolve malicious domains outside the gateway path. Auditors will expect DNS-layer enforcement or an equivalent control that blocks resolution and is provably applied. ¹

How do we handle devices that use hardcoded DNS servers?

Treat it as a known exception class: segment those devices, control DNS at the network boundary where possible, and monitor their DNS behavior closely. Record the exception and tie it to a remediation plan (firmware update, replacement, or redesign). ¹

What DNS logs are “enough” for auditors?

Collect query/response data that lets you attribute activity to a system or user and show the policy action taken (allowed, blocked, sinkholed). Keep example investigations that prove you reviewed alerts and acted. ¹

We allow DoH in browsers; is that automatically noncompliant?

Not automatically, but it creates a control gap if DoH bypasses your filtering and monitoring. Decide whether to restrict DoH to sanctioned resolvers, enforce filtering at the endpoint, or block unmanaged DoH endpoints, then document and test the approach. ¹

How should a Health IT vendor scope this if we host in cloud?

Start with your recursive resolver path inside your cloud networks, ensure DNS filtering and logging cover production workloads, and extend policy to corporate endpoints and CI/CD systems. Be explicit about shared responsibility boundaries and what you control. ¹

Footnotes

1. HICP 2023 - 405(d) Health Industry Cybersecurity Practices