How To Perform A Deep Dive Into DNS Security And Filtering

DNS is often treated as background plumbing, yet it influences almost every connection made by a business. A compromised resolver, weakly protected authoritative server, or poorly governed filtering rule can expose staff, customers, cloud workloads, and sensitive systems to phishing, malware, command-and-control traffic, and data theft.

For Australian organisations, DNS security also sits within a wider governance picture. A business using NBN connectivity, Microsoft 365, public cloud, remote workforces, and customer-facing applications needs visibility across offices in Sydney, Melbourne, Brisbane, Perth, and regional locations. A structured review can reveal gaps that ordinary firewall checks miss.

Map The Entire DNS Environment

Start by identifying every authoritative DNS zone, recursive resolver, forwarding path, registrar account, and third-party DNS provider. Include forgotten subdomains, development environments, content delivery networks, SaaS platforms, and cloud resources created by separate teams. Asset discovery should compare DNS records with certificate logs, cloud inventories, vulnerability scanners, and domain registration data.

Document who can create, modify, and delete records. Pay close attention to delegated subdomains and external providers, since a single unmanaged zone can become a route into a trusted brand. Australian government and regulated organisations should also connect this inventory to Essential Eight maturity planning and internal risk registers.

Examine Resolver And Authoritative Server Security

Separate recursive and authoritative functions wherever practical. Recursive resolvers should accept queries only from approved networks, while authoritative servers should expose only the services required to answer public requests. Restrict zone transfers, disable open recursion, patch DNS software, and protect management interfaces with multifactor authentication and privileged access controls.

Review configuration for DNSSEC, secure dynamic updates, split-horizon DNS, and appropriate time-to-live values. DNSSEC can help validate record authenticity, although it requires disciplined key management and rollover procedures. Test failures and expired signatures before relying on them in production, particularly when DNS supports critical healthcare, financial, or e-commerce services.

Analyse Query Behaviour And Attack Signals

A deep assessment examines query volume, response codes, requested domains, record types, client identity, and time-based patterns. Look for unusually long subdomain labels, high volumes of TXT requests, repeated NXDOMAIN responses, fast-flux behaviour, and algorithmically generated domains. These indicators can point to malware, DNS tunnelling, domain generation algorithms, or misconfigured applications.

Compare activity against known threat intelligence and internal baselines. A mining site in Western Australia may have a very different normal traffic pattern from a Melbourne online retailer, so generic thresholds can create unnecessary alerts. Monitoring should distinguish business-driven spikes from suspicious behaviour and retain enough context for investigation.

Design Filtering Around Risk And Roles

DNS filtering works best when policies reflect users, devices, applications, and locations. Block known malware, phishing, botnet, newly registered, and high-risk domains, while applying stricter controls to unmanaged devices and sensitive server networks. Create controlled exceptions with owners, expiry dates, and business justification rather than allowing permanent allow-list entries.

Filtering should also cover roaming laptops, mobile devices, guest networks, and cloud workloads. Consider secure DNS forwarding, DNS over HTTPS governance, and endpoint controls so staff cannot easily bypass organisational policy. For Australian workplaces, policies should support flexible and hybrid arrangements without disrupting legitimate access to local suppliers, government portals, or essential industry services.

Connect DNS To Detection And Response

Send resolver, authoritative, firewall, endpoint, and identity data into a SIEM where analysts can correlate DNS events with authentication and network activity. A sudden query to a suspicious domain followed by a privileged login or unusual outbound transfer deserves a higher priority than either event alone. Retention periods should support investigations, compliance needs, and practical storage budgets.

Good log management practices make DNS evidence useful during incident response. Define alert ownership, escalation paths, and playbooks for sinkholing domains, isolating endpoints, blocking indicators, and preserving evidence. Test those procedures through tabletop exercises rather than assuming an alert will automatically produce a fast response.

Test Filtering Without Creating Blind Spots

Use controlled simulations to test whether malicious domains, lookalike sites, tunnelling attempts, and newly registered domains are detected or blocked. Validate logging, alert routing, user notifications, and exception workflows at the same time. Penetration testing can assess whether attackers can bypass DNS controls through alternative resolvers, encrypted tunnels, hard-coded IP addresses, or compromised cloud services.

Measure false positives as carefully as blocked threats. Overly aggressive filtering can encourage staff to seek workarounds, while weak policies create a false sense of safety. Review performance during peak periods and outages, including failover to secondary resolvers and the behaviour of remote users when corporate DNS is unavailable.

Prioritise Sustainable DNS Controls

A DNS programme should have clear ownership between security, infrastructure, network, cloud, and application teams. Establish change approval, regular access reviews, configuration backups, domain expiry checks, and scheduled rule reviews. Track metrics such as blocked malicious queries, investigation time, policy exceptions, DNSSEC status, and resolver availability.

The following actions provide a practical starting point:

• Inventory all zones, resolvers, delegated domains, and third-party DNS services.
• Disable open recursion and restrict zone transfers to approved systems.
• Enforce multifactor authentication for registrars, DNS platforms, and administrators.
• Centralise DNS telemetry in a SIEM with useful retention and alert context.
• Apply role-based filtering to staff, guests, servers, mobile devices, and cloud workloads.
• Test bypass methods, failover behaviour, and incident response playbooks.
• Review policies against the Privacy Act, contractual duties, and sector obligations.

DNS security should be reviewed after mergers, cloud migrations, office changes, major application releases, and new remote access deployments. In Australia, requirements can vary sharply between an APRA-regulated financial institution, a state government department, a healthcare provider, and a growing Brisbane e-commerce business.

A security partner can combine DNS review with vulnerability assessment, penetration testing, cloud and mobile security checks, SIEM monitoring, and threat intelligence. Infoziant Security can help establish a tailored assessment, including a free VAPT report or trial-based engagement, so your organisation can identify DNS weaknesses before they become an incident.