DNS sits at the foundation of every internet-connected service your business operates. Every website visit, email delivery, and cloud application connection starts with a DNS lookup. Despite this critical role, DNS security receives a fraction of the attention that organisations devote to firewalls, endpoint protection, and access management.
Attackers understand this blind spot. DNS hijacking, cache poisoning, and subdomain takeover attacks redirect traffic silently, sending your customers to phishing sites, intercepting email, or impersonating your services without triggering traditional security alerts. The damage happens before anyone notices something is wrong.
How DNS Attacks Work
Subdomain takeover is alarmingly simple to execute. When an organisation creates a DNS CNAME record pointing to a cloud service like Azure, AWS, or a CDN provider, then later decommissions that cloud resource without removing the DNS record, anyone can claim the orphaned subdomain. An attacker registers the same cloud resource name and suddenly controls a subdomain under your domain, complete with your SSL certificate trust and domain reputation.
DNS tunnelling uses the protocol itself as a covert communication channel. Malware on a compromised system encodes stolen data within DNS queries, sending it to attacker-controlled nameservers. Because DNS traffic is rarely inspected at the same depth as HTTP or SMTP, the exfiltration bypasses content inspection tools and data loss prevention systems entirely.
William Fieldhouse, Director of Aardwolf Security Ltd, comments: “DNS is the one protocol that every organisation depends on and almost nobody monitors properly. We find dangling DNS records in nearly every external assessment. Each one represents a potential subdomain takeover that would let an attacker host convincing phishing content under your legitimate domain. The fix takes minutes. Finding them requires systematic testing.”
Protecting Your DNS Infrastructure
Implement DNSSEC to prevent cache poisoning attacks. Deploy DNS monitoring that alerts on record changes, particularly for MX records that control email routing and A/CNAME records for customer-facing services. Review DNS records quarterly and remove any entries that point to decommissioned resources.
Include DNS assessment within your external network penetration testing scope. Testers should enumerate subdomains, check for takeover opportunities, and verify that DNSSEC is properly configured. These checks take minimal time but uncover risks that could facilitate convincing impersonation attacks against your customers and partners.
Run vulnerability scanning services that include DNS-specific checks alongside traditional port and service scanning. Orphaned subdomains, zone transfer vulnerabilities, and misconfigured SPF records all create exploitable weaknesses that automated scanners can identify on a continuous basis.
Zone transfer vulnerabilities, whilst less common than they once were, still appear in assessments. A misconfigured DNS server that permits zone transfers to any requestor hands attackers a complete map of your domain infrastructure, including internal hostnames and IP addresses that inform subsequent attack planning.
Consider implementing DNS response rate limiting to mitigate reflection and amplification attacks that abuse your own DNS infrastructure. An open recursive resolver on your network can be weaponised against third parties, creating legal and reputational exposure alongside the direct security risk.
DNS security deserves the same attention as any other critical infrastructure component. The protocol underpins everything your business does online. Securing it properly prevents attack categories that most organisations have not even considered.
