Dangling DNS Attack Allows Hackers to Take Over Organization’s Subdomain

Hackers are exploiting what’s known as “Dangling DNS” records to take over corporate subdomains, posing significant threats to organizations’ security frameworks.

This attack vector has been increasingly noted by security teams, highlighting the need for constant vigilance in DNS configuration management.

A New Threat Landscape

Subdomain takeovers occur when a misconfigured or unused subdomain’s DNS entry, particularly canonical name (CNAME) records, points to an expired or non-existent service.

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This scenario, termed “Dangling DNS,” not only involves CNAME records but also other DNS record types like NS, MX, A, and AAAA.

When organizations discontinue a service or fail to update DNS entries post-service termination, attackers can register the abandoned subdomain with the service provider, gaining control over it.

For instance, if a company’s help desk subdomain was previously hosted on a SaaS platform like Zendesk and the service was terminated without updating the DNS, an attacker could initiate a free trial with the same provider under the company’s subdomain, thus taking control.

Cloud service misconfigurations present another avenue for these attacks.

If an organization deletes a cloud resource like an AWS S3 bucket used for hosting a static website without removing or updating the corresponding DNS entries, attackers can register a new bucket with the same subdomain name, redirecting and potentially maliciously modifying traffic.

A recent research investigation from October 2024 to January 2025 by security researchers found approximately 150 S3 buckets, previously owned by major corporations and government agencies, that were deleted but still referenced by outdated DNS records.

Over 8 million requests were made to these non-existent buckets, seeking various critical resources like container images and SSLVPN server configurations.

The Supply Chain Risk

The implications extend beyond mere website defacement or credential theft, which are traditional outcomes of subdomain takeovers.

With organizations using subdomains to distribute software updates, cloud service templates, and other critical assets, an attacker could inject malicious code into these supply chains, leading to potential remote code execution (RCE), resource hijacking, or even persistent backdoors.

SentinelOne, a cybersecurity firm, has identified over 1,250 instances of subdomain takeover risks due to deprovisioned cloud resources in the past year.

They advocate for robust security practices across the entire software development lifecycle, emphasizing that runtime security is critical, especially when involving third-party services.

This emerging threat underscores the importance of meticulous DNS management.

Organizations must ensure their subdomains are either actively used or securely decommissioned, removing all associated DNS records to prevent exploitation. 4

As the cyber landscape evolves, maintaining proactive security measures through vigilant monitoring and timely updates to cloud and DNS configurations is paramount to safeguarding against these sophisticated attacks.

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