Dangling CNAMEs: The Critical DNS Misconfiguration Most Organizations Still Miss

In cybersecurity, the most damaging attacks are not always the most sophisticated. Sometimes, they begin with something as mundane as a forgotten DNS record.

That reality came into sharp focus when researchers uncovered a large-scale campaign involving hijacked university subdomains across institutions including UC Berkeley, Columbia University, and Washington University in St. Louis. Attackers exploited abandoned CNAME records to take control of trusted .edu subdomains and use them to host pornography, scams, fake applications, and malware delivery infrastructure.

The attack did not rely on zero-days, ransomware, or advanced intrusion techniques. It exploited a critical DNS misconfiguration that continues to exist across enterprises worldwide: dangling CNAMEs.

And while universities became the headline, the underlying issue affects every organization operating in the cloud.

The Misconfiguration That Refuses to Go Away

A dangling CNAME occurs when a DNS record continues pointing to a cloud resource that no longer exists.

For example, an organization may create a subdomain for a temporary application hosted on AWS, Azure, GitHub Pages, or another cloud platform. Once the project ends, the underlying resource is decommissioned — but the DNS record remains active.

That abandoned record creates an opening.

An attacker who identifies the orphaned reference can claim the cloud resource name and effectively inherit control of the organization’s trusted subdomain. From that point onward, legitimate traffic is routed directly to attacker-controlled infrastructure.

In the recent .edu campaign, threat actors leveraged this technique at scale. Hijacked university subdomains began serving explicit content, fake CAPTCHA pages, malicious downloads, and tech-support scams. Because the domains belonged to highly trusted educational institutions, many of the malicious pages ranked prominently in search engine results.

Why This Has Become a Cloud-Era Security Problem

Dangling CNAMEs are not new. What has changed is the scale and complexity of modern cloud infrastructure. Organizations now create and retire cloud assets constantly:

• Development environments
• Temporary marketing sites
• Regional applications
• Vendor integrations
• Sandbox deployments
• Migration workloads
• Short-lived testing infrastructure

Infrastructure lifecycles have become increasingly dynamic. DNS management practices, however, often remain manual, fragmented, and disconnected from cloud operations. This creates a persistent visibility gap.

The teams provisioning cloud resources are rarely the same teams maintaining DNS records. Developers may terminate services without notifying network administrators. Third-party platforms may be removed while associated DNS entries remain untouched for months or years. The result is DNS sprawl — an expanding inventory of records that no longer accurately reflects the organization’s active infrastructure.

Attackers understand this well. Groups like Hazy Hawk reportedly automate the discovery of orphaned DNS entries tied to abandoned cloud services. Their operations demonstrate how profitable this attack path has become. Trusted subdomains can be weaponized for phishing, malware delivery, SEO manipulation, scam distribution, and traffic monetization with relatively little effort.

Why Traditional Security Controls Often Miss It

Many organizations assume their existing security stack already covers this problem. In reality, dangling CNAME detection frequently falls outside the visibility scope of traditional tools.

Endpoint security solutions cannot detect abandoned DNS references. Vulnerability scanners often focus on exposed services rather than inactive infrastructure relationships. Cloud security posture management platforms may monitor workloads but not continuously validate external DNS dependencies.

Even enterprise DNS platforms typically emphasize availability, performance, and protection against attacks like DDoS or cache poisoning — not orphaned record discovery. This creates an uncomfortable reality: organizations may invest heavily in advanced detection capabilities while leaving behind basic DNS exposures that attackers can exploit in plain sight. The issue is not a lack of security technology. It is the absence of continuous DNS posture visibility.

The Risk Is Reputational

The technical mechanics of a dangling CNAME takeover are relatively straightforward. The business consequences are not. When attackers hijack a trusted subdomain, they inherit more than routing control. They inherit reputation.

That reputation affects:

• Search engine trust
• Customer confidence
• Email deliverability
• Brand credibility
• Third-party integrations
• Regulatory scrutiny

This is precisely why attackers target government agencies, healthcare organizations, universities, and large enterprises. The domain itself becomes an asset.

For organizations in regulated industries, the implications can escalate quickly. A compromised subdomain distributing malware or harvesting credentials may trigger incident response obligations, compliance reviews, or reputational fallout disproportionate to the technical simplicity of the attack.

DNS Hygiene Is No Longer Enough

For years, dangling DNS records were treated as periodic cleanup tasks. That mindset no longer reflects the reality of modern infrastructure.

DNS environments are changing continuously. Cloud assets appear and disappear daily. External dependencies evolve rapidly. Manual audits performed quarterly or annually cannot keep pace with the speed of infrastructure change.

Organizations need continuous DNS posture management rather than reactive DNS maintenance.

This includes:

• Discovering orphaned DNS records
• Monitoring deprovisioned resources
• Detecting takeover-prone configurations
• Identifying stale third-party integrations
• Continuously validating DNS integrity across environments

Most importantly, DNS security must become integrated into infrastructure lifecycle management rather than treated as a separate administrative process. If infrastructure can be provisioned automatically, DNS validation must also be automated.

Why DNSPM Is Becoming Essential

The university hijacking campaign exposed a broader industry reality: DNS remains one of the least monitored components of the external attack surface. Organizations spend enormous effort securing endpoints, identities, and applications while DNS often operates quietly in the background — until something goes wrong.

This is where DNS Posture Management (DNSPM) becomes critical.

Rather than focusing solely on DNS availability or performance, DNSPM continuously evaluates DNS configurations for security risks, orphaned assets, exposure gaps, and takeover opportunities.

For organizations operating across multi-cloud environments, third-party platforms, and decentralized infrastructure teams, that visibility becomes increasingly important.

CheckRed’s DNSPM solution helps organizations uncover hidden DNS risks before attackers do. By continuously identifying dangling CNAMEs, abandoned DNS relationships, and takeover-prone configurations, organizations can reduce one of the most underestimated attack surfaces in modern infrastructure.