Dangling DNS attacks rarely make headlines, probably because they usually don’t include zero-day exploits or sophisticated malware. Instead, attackers are simply taking advantage of forgotten infrastructure, abandoned services, and DNS records no one remembered to clean up.
For attackers, this makes dangling DNS records an easy win. For organizations, it’s a blind spot that can quietly undermine your brand’s reputation, trust, and security.
Understanding dangling DNS
To understand why dangling DNS records are so risky, it’s helpful to start with how DNS is supposed to work — and what happens when it doesn’t.
Think of DNS records as signposts that direct traffic to the services and systems your organization owns and operates. When those signposts point somewhere that no longer exists (or no longer belongs to you), the door is left wide open for a DNS attack.
Here’s what you need to know about the risks of dangling DNS and how to protect yourself against dangling DNS attacks.
What’s a dangling DNS record?
A dangling DNS record is a DNS entry that points to a resource that either no longer exists or is no longer controlled by the organization that owns the domain. The DNS record is still live, but the destination it references is gone.
That mismatch creates an opportunity for someone else to step in and claim it. And that someone else is often an attacker looking for an opportunity to impersonate your brand, hijack a trusted subdomain, or launch a phishing campaign, all without needing to compromise your system directly.
The meaning of dangling DNS
Dangling DNS records aren’t created with bad intent. They’re the result of normal business operations: cloud migrations, vendor changes, expired trials, or services that were quickly spun up and later forgotten.
From a DNS perspective, everything may look valid. But from a security perspective, those leftover records represent unclaimed territory that attackers can exploit with minimal effort.
The threat of dangling DNS attacks
Dangling DNS attacks are especially dangerous because they don’t always look like attacks. There’s no breach alert, no malware signature, no system outage to draw attention.
Instead, attackers take advantage of the trust your domain already has. This makes malicious activity harder for you to detect and more convincing for users, customers, and even email filters.
Subdomain takeover: a real dangling DNS attack risk
Dangling DNS records are a leading cause of subdomain takeover.
In subdomain takeover, an attacker claims control of a subdomain belonging to a legitimate organization. That subdomain can then be used to host malicious content, push phishing campaigns, or impersonate trusted services.
Types of dangling DNS records
Not all dangling DNS records are the same. Some pose a higher risk of attack because they leave the door open wider for attackers.
Dangling A records
A dangling A record points a domain or subdomain to an IP address that’s no longer assigned to your organization. If that IP address is later reused by a cloud provider or hosting service, an attacker may be able to claim it and host content that appears to come from your domain.
Often, that content will be used to aid phishing, distribute malware, or host fake login portals — all in an attempt to scam unsuspecting users or customers who think they’re interacting with your trusted brand.
Dangling CNAME records
Dangling CNAME records often leave you most vulnerable. They point your subdomain to a third-party service that no longer exists or is no longer under your control.
If that service allows custom domain claims, an attacker can register the abandoned destination and immediately take over your subdomain — often without triggering alerts. If you’re not proactively managing and monitoring your DNS records, attackers can use this method to run scams for quite some time before you notice.
Dangling NS records
Dangling NS records delegate control of your subdomain to name servers that no longer exist or are no longer managed by your organization. This effectively hands DNS resolution for your subdomain to the attacker, allowing them to create new records, redirect traffic, or intercept mail, all while operating under your domain’s name.
Identifying dangling DNS entries
Finding dangling DNS entries isn’t the most fun you’ll have this week, but it’s far easier than dealing with the fallout of an attack.
Manual detection methods
If you’re manually searching for dangling DNS entries, start with an inventory of your DNS records.
Look for entries pointing to:
- Cloud services that are no longer in use
- Third-party platforms that have been shut down
- IP addresses that no longer belong to your organization
You can also attempt to resolve each DNS entry and check whether the specified destination responds as expected. If the destination doesn’t respond, that tells you the record may be dangling.
Note that manual reviews work best for smaller companies. As DNS sprawl increases, manual detection methods will become harder for you to manage and can compromise security over time. Automated solutions like Valimail can help you monitor effectively as you grow.
Automated solutions for detection
If you’re working on behalf of a large organization, automated solutions can help you scan DNS records at scale and flag entries that point to unclaimed or unreachable resources. Some tools focus specifically on subdomain takeover risks, while others include dangling DNS detection as part of broader DNS hygiene and security monitoring.
Remember that automation doesn’t eliminate the need for human review, but it does make it much easier for you to spot dangling DNS records before potential attackers do.
Preventing dangling DNS issues
The good news here is that dangling DNS attacks are preventable. A few smart, consistent habits go a long way in safeguarding your company.
Best practices for DNS management
One of the best ways to protect your organization: Ensure that every DNS record exists for a reason and stays under your control.
Here are some guidelines to follow:
- Document why each DNS record exists and who owns it
- Avoid creating DNS entries “just in case”
- Limit who can add or modify DNS records
- Remove DNS records when decommissioning services
Regular auditing and monitoring
DNS records should be reviewed regularly, not just when something breaks.
Schedule regular audits to catch stale records, forgotten subdomains, and misconfigurations. And pair these audits with regular monitoring — manual or automated — to add another layer of security and help you catch unexpected DNS changes.
Protect your DNS with Valimail
Dangling DNS records don’t exist in isolation. They’re part of a broader domain security ecosystem that includes email authentication, domain reputation, and brand protection.
Valimail can help you maintain visibility and control over how your domains are used, especially in email. By strengthening authentication and monitoring activity, we help you prevent misconfigurations, reduce risk, and ensure only authorized sources are sending on your behalf.
Talk with our team to get a clearer picture of your DNS records and risk of attack.
Frequently asked questions about dangling DNS
Why is dangling DNS dangerous?
Attackers can use dangling DNS records to hijack subdomains, run phishing campaigns, or serve malicious content — and they can do all of this while essentially “posing” as your trusted brand.
Can dangling DNS lead to email security problems?
Yes. If attackers gain control of your subdomain, they can send email appearing to come from your domain while undermining authentication protocols like SPF, DKIM, and DMARC.
How common are dangling DNS vulnerabilities?
Dangling DNS is surprisingly common, especially in fast-growing companies or organizations that use multiple cloud services or third-party platforms where records are created quickly and not closely managed or cleaned up.
How can I prevent dangling DNS attacks?
Clear ownership of DNS records, regular audits, ongoing monitoring, and removing entries for decommissioned services can drastically reduce your risk of dangling DNS attacks. Valimail can help.
