Subdomain Takeover and Orphaned DNS Records: Hidden Risks for Your Domain, Brand and SEO

Subdomain takeover and orphaned (also called dangling) DNS records look like edge‑case security topics, but they are quietly present in almost every medium and large domain portfolio we review at dchost.com. A forgotten “oldapp.yourbrand.com” record pointing to a retired SaaS, a staging subdomain left after a campaign, a CDN CNAME that no longer has an active configuration – all of these can be turned into an attack surface. The problem is not just technical: a successful takeover can damage your brand, inject malware under your name, and undo years of SEO work in a few days.

In this article we will walk through what subdomain takeover actually is, how orphaned DNS records are created in real life, and why search engines and users treat them as your responsibility. We will also cover practical detection and prevention techniques you can apply on any DNS stack, and how to recover if you discover that a subdomain has already been abused. The goal is not to scare you, but to give you a clear checklist you can implement across your domains, hosting, VPS and DNS infrastructure.

What Is Subdomain Takeover?

Subdomain takeover happens when a subdomain of your domain (for example: “blog.example.com” or “files.example.com”) points via DNS to an external service that is no longer under your control – but is still reusable by anyone else. An attacker (or even just an opportunistic spammer) can claim that resource and start serving their own content under your subdomain, using the trust of your main domain as a shield.

Typically, the pattern looks like this:

• You create a DNS record like app.example.com CNAME some-service.com for a SaaS, CDN, object storage bucket or PaaS.
• Later, you delete the app, storage bucket, project, or hosting configuration at that provider.
• The DNS record remains in place, still pointing to that external hostname.
• The external platform now shows that the resource name (e.g. “app”) is available to register.
• An attacker registers that resource and instantly controls app.example.com for as long as your DNS record stays.

From the browser, nothing looks obviously wrong: the URL is on your domain, the SSL certificate can be valid, and the content is fully controlled by the attacker. This is why subdomain takeover is so dangerous for both security and brand trust.

What Are Orphaned / Dangling DNS Records?

Orphaned DNS records (also known as dangling DNS) are DNS entries that no longer have a valid, intended target. The record continues to exist in your zone, but the server, bucket, service or IP it points to is unused, unassigned, or owned by someone else.

Common examples include:

• CNAMEs to SaaS platforms or object storage that were deleted.
• A or AAAA records pointing to IP addresses that are no longer assigned to your server.
• MX records for a mail provider you no longer use.
• TXT and CNAME records created for one‑off validations (SSL, email, search consoles) that are never cleaned up.

Not all orphaned DNS records are immediately exploitable, but many of them are. Where there is a platform that lets others register the same hostname, you have a potential subdomain takeover risk. Where there is a re‑assigned IP, you have a risk of traffic, cookies or API calls being sent to a random system that is not under your control.

If you want a deeper, platform‑specific implementation view, we have a separate hands‑on guide to preventing subdomain takeover and dangling DNS on Cloudflare and cPanel. In this article, we will stay at the strategy and process level.

How Do Orphaned DNS Records Appear in Real Projects?

In theory, every project has clean documentation and a tidy DNS zone. In reality, hosting stacks change, teams rotate, and temporary experiments become forgotten leftovers. Here are some of the most common paths we see in audits at dchost.com.

1. Short‑Lived Marketing and Campaign Subdomains

Marketing and growth teams love to move fast. They launch landing pages on “spring-sale.example.com” or “try.example.com” using external landing page builders or marketing automation platforms. After the campaign ends, the subscription is cancelled, but the DNS record often survives.

Months later, the external platform shows that subdomain name as available within their system. An attacker can claim it and instantly serve phishing pages, fake login forms or malware under your old campaign URL – and users will still recognise it as your brand.

2. Staging and Test Environments

Engineering teams create staging or test environments on subdomains like “staging.example.com”, “test-api.example.com” or “dev-store.example.com”. These often live on separate VPS instances or experimental PaaS projects.

When the project is cleaned up, the server or SaaS project is deleted, but DNS is not always part of the decommission checklist. As we explain in our article on noindex, password and IP restriction strategies for staging environments, test subdomains already carry higher risk. When they are both exposed and orphaned, they become attractive takeover targets.

3. Provider, IP or Hosting Changes

When you migrate from one server or hosting plan to another, you usually change A and AAAA records. If old records remain in the zone and those IPs get re‑assigned later, someone else now receives traffic for those hostnames.

While this is not always a “classic” subdomain takeover scenario, it can still be abused: a hostile recipient of that IP range can present a valid HTTPS site, capture cookies, or host phishing pages under your subdomain. Following a structured domain and DNS migration checklist when changing hosting provider helps avoid those leftovers.

4. SaaS and Third‑Party Integrations

Modern sites rely heavily on SaaS tools: helpdesks, documentation portals, community forums, email marketing, status pages and more. Most of these services allow custom domains or subdomains like “support.example.com” or “status.example.com”.

When you cancel or move away from a vendor, it is common to disable the integration inside their platform, but forget to:

• Delete the DNS CNAME that points to their hostname.
• Remove TXT records used for domain verification.
• Adjust HTTP redirects to a new location.

This leaves a dangling connection between your DNS and a third‑party system that may be re‑used by other customers – or attackers.

Security, Brand and SEO Impact of Subdomain Takeover

From a technical perspective, a subdomain takeover is “just” content served from a place you do not control. From a business perspective, it is much more: users see your domain, search engines index that content as yours, and attackers use this trust to bypass many instinctive safety filters.

1. Security Impact

• Phishing and credential theft: Attackers often deploy login pages that look like your real site and steal usernames, passwords, card details or internal credentials. Because the URL is under your domain, users and even staff are more likely to enter sensitive data.
• Malware distribution: Takeovered subdomains are frequently used to host malicious JavaScript, drive‑by downloads or fake software updates. If your main site references assets from that subdomain (old JS/CSS URLs, iframes, images), the attack can chain into your active site.
• Session and cookie abuse: Depending on cookie scope settings (e.g. Domain=.example.com), a hostile subdomain might access or set cookies that affect authentication or user tracking on your main site. Proper cookie scoping and modern SameSite attributes are essential here, as we discuss in our guide on configuring secure cookies with SameSite, Secure and HttpOnly flags.
• Abuse of internal APIs: Some organisations whitelist *.example.com in CORS, CSRF or firewall rules. A hostile subdomain may be able to call internal APIs or abuse lax origin checks.

2. Brand and Legal Impact

To the outside world, a subdomain is part of your brand – there is no practical distinction between “www.example.com” and “download.example.com” for most users. If one of them hosts:

• Scams or fake giveaways,
• Adult content,
• Pirated software, or
• Political or misleading material,

your brand becomes attached to that activity. Even if you are blameless technically, regulators, partners and customers will expect you to own and fix the problem. In serious cases, this can trigger legal questions around negligence in managing your domain and DNS.

3. SEO and Reputation Impact

Search engines treat subdomains of a site as part of the same overall entity. Abuse of one subdomain can negatively impact the perceived quality and safety of the entire domain.

Potential SEO consequences include:

• Manual actions or penalties: If a taken‑over subdomain hosts spam, malware or thin content, it can trigger manual actions that affect your main domain’s rankings.
• Loss of trust signals: Being listed on malware or phishing blacklists (including browser warning lists) for any subdomain reduces user trust and click‑through rates across your entire domain.
• Index pollution: Attackers might generate thousands of low‑quality pages under your subdomain, diluting your brand’s index and affecting crawl budget.
• Broken link equity: Old backlinks pointing to legitimate content on that subdomain get re‑used for spam or affiliate schemes, damaging the way search engines interpret your link profile.

We see this problem often when companies buy expired or aged domains without proper checks. Our guide on buying expired or used domains with SEO and security checks covers this angle in more depth.

How to Detect Vulnerable Subdomains and Orphaned DNS Records

Prevention starts with visibility. You cannot protect or clean up what you do not know exists. In practice, detection is a mix of inventory, automated scanning, and process.

1. Build a Complete DNS and Subdomain Inventory

First, you need a reliable, current list of all subdomains and DNS records under your domains. That means:

• Exporting zone files or record lists from your DNS provider or registrar.
• Including all record types: A, AAAA, CNAME, MX, TXT, SRV, CAA and NS for delegated sub‑zones.
• Documenting which business owner, team or system “owns” each subdomain.

If you manage dozens of domains (agencies, resellers, holding groups), a recurring DNS audit is essential. Our hosting and DNS audit checklist for agencies shows how to integrate this step when onboarding or reviewing client infrastructure, but the same idea applies to internal portfolios.

2. Identify High‑Risk Record Patterns

Once you have an inventory, focus on record patterns that commonly produce subdomain takeover risks:

• CNAMEs to well‑known SaaS, PaaS, CDN, storage and site‑builder platforms.
• A/AAAA records pointing to IP ranges that no longer belong to your servers or providers.
• Subdomains used for marketing campaigns, experiments, staging and temporary projects.
• MX/TXT records for email providers you have stopped using.

Mark these records for verification with the responsible owner (marketing, dev team, product, etc.).

3. Automate Basic Checks

Some checks can be scripted or integrated into your monitoring tools:

• HTTP checks: For every A/AAAA/CNAME record that should serve web content, periodically make HTTP/HTTPS requests and look for tell‑tale messages like “No such app”, “This site is not configured”, or default error pages from third‑party platforms.
• DNS resolution status: Ensure that CNAME targets resolve and do not return NXDOMAIN. A CNAME pointing to a non‑existent hostname is a classic dangling DNS pattern.
• IP ownership: Use WHOIS or RIPE/APNIC/ARIN lookups to confirm that IP addresses still belong to your expected provider or network.

These checks are not a full replacement for specialised security tools, but they capture a large percentage of real‑world problems with very little effort.

4. Integrate DNS and Hosting Changes into Your Processes

Technical detection only works if your processes support it. Key points to integrate into your internal runbooks:

• Change management: Any project decommission (SaaS subscription cancellation, VPS removal, app shutdown) must include a DNS review step.
• Ownership tagging: Every new subdomain should have an internal owner (team, system, or person) documented in your inventory.
• Periodic review: At least once or twice a year, run a domain and DNS review to catch long‑forgotten records.

Our article on the most common DNS mistakes and 10 records to check is a useful companion checklist for this step.

Prevention Strategies: DNS Hygiene and Hosting Architecture

After you know where you stand, the next step is preventing new dangling records from appearing and reducing the blast radius if something slips through.

1. Treat DNS as Part of Your Application Lifecycle

DNS is often managed separately from development and deployment workflows, but it directly reflects your application architecture. To avoid orphaned records:

• Include DNS creation and removal in your deployment automation (CI/CD) when possible.
• For manual DNS changes, require a ticket or change request with a clear expiration or ownership field.
• When you retire a feature or product, your decommission checklist must include a DNS and subdomain cleanup step.

2. Limit Broad Wildcards and Delegations

Wildcards like *.example.com and delegated sub‑zones can be convenient, but they also increase the risk surface:

• Do not delegate large parts of your namespace to external providers unless necessary.
• Avoid wide wildcards that point entire sub‑trees to third parties.
• Prefer explicit subdomain mappings (e.g. “blog”, “shop”, “status”) with clear ownership.

This makes it easier to track, audit and reason about every subdomain’s purpose and risk profile.

3. Use Clear Naming Conventions for Temporary and Internal Subdomains

Naming conventions help your team identify which subdomains are safe to remove and which ones are long‑term. For example:

• Prefix temporary marketing subdomains with “campaign-” and include the year or quarter.
• Use clearly internal names like “int-“, “dev-“, or “staging-” for non‑public environments, and protect them with IP filtering or VPN.
• Document these patterns in your internal wiki or runbooks.

Combined with access control and noindex/password protection (as covered in our staging and test environment hardening guide), this reduces both takeover and accidental exposure risks.

4. Harden Cookie and Origin Policies

Even if a subdomain is taken over, you can limit what damage it can do:

• Scope sensitive cookies (login, sessions, admin) to the exact host (e.g. “www.example.com”) instead of the whole domain.
• Use SameSite, Secure and HttpOnly cookie attributes to reduce cross‑site and JavaScript access vectors.
• Restrict allowed origins in CORS and CSRF checks to known, required hosts instead of *.example.com.

These are your safety nets if a hostile subdomain appears somewhere in your namespace.

5. Strengthen Overall Domain Security

Subdomain takeover is one part of the broader picture of domain security. Enforcing strong protection at the registrar and DNS layers reduces the chance of attackers adding or modifying records directly. At a minimum, you should consider:

• Registrar lock and transfer lock on valuable domains.
• DNSSEC where supported and appropriate.
• 2FA on registrar and DNS management accounts.

Our domain security best practices guide on registrar lock, DNSSEC, Whois privacy and 2FA explains how to set these up safely and when to prioritise them.

Subdomain Takeover and SEO: Recovery Plan if It Already Happened

Discovering that a subdomain has been taken over or abused is stressful, but you can recover if you move methodically. Here is a practical plan we recommend to customers.

1. Regain Technical Control

Your first priority is to stop serving malicious content:

• Remove or correct the offending DNS record to point to an asset you control.
• If the subdomain is no longer needed at all, delete its records or redirect it (301) to a relevant, owned URL.
• Flush DNS caches where possible (by lowering TTLs beforehand, if you have the chance).

Keep in mind that DNS changes take time to propagate. Users and crawlers may still see old content for a while, depending on previous TTL values. Our article on DNS TTL best practices can help you design a TTL strategy that balances performance, flexibility and incident response.

2. Clean Up in Search Consoles and Analytics

Next, signal to search engines that the problem is resolved and that you are cleaning up:

• Verify the affected subdomain (or the entire domain property) in your search console.
• Check for manual actions, security issues or malware warnings and follow the documented reconsideration process.
• Review indexed URLs under that subdomain and request removal for clearly malicious or irrelevant pages.

If the subdomain had significant legitimate content in the past, consider where that content now lives and set up appropriate 301 redirects so that link equity is preserved while spam pages are removed.

3. Check Blacklists and Email Reputation

Many phishing and malware incidents end up on security feeds and blacklists that browsers and mail providers consult. You should:

• Check your domain and key subdomains against major malware and phishing lists.
• If email was involved, review your sender reputation and spam complaints.
• Follow removal procedures after you have fixed the root cause.

We have a dedicated guide on getting removed from Google Safe Browsing and email blacklists that walks through this process step‑by‑step.

4. Communicate Internally and, If Needed, Externally

Internal communication is essential so that support, marketing and management teams know what happened and how to respond to user questions. For severe incidents, a short external statement may be appropriate, especially if customers encountered phishing or malware under your domain.

Transparency, combined with clear remediation steps, tends to minimise long‑term trust damage.

How dchost.com Fits Into a Safer Domain and DNS Strategy

At dchost.com we see subdomain takeover and orphaned DNS issues most often in environments where DNS, hosting and domain management are split between many providers and teams, with no single point of responsibility. While you can never fully remove human error, you can build an infrastructure that makes it much harder for problems to slip through unnoticed.

Depending on your size and technical preference, there are a few patterns we frequently implement with customers:

• Centralised DNS management: Keep authoritative DNS for your domains under a single, well‑governed system. Use clear roles, 2FA and documented change procedures.
• Consistent naming and documentation: Align your hosting, VPS, dedicated server or colocation architecture with naming conventions in DNS, so each subdomain maps cleanly to a known system.
• Regular reviews: Combine periodic DNS audits with hosting inventory reviews. When a VPS or application is decommissioned, DNS is part of the closure process.

If you already host with dchost.com, our support team can help you review your current DNS zones, suggest clean‑up steps and recommend safer patterns for future projects. If you are planning new domains, rebranding, or a hosting migration, this is an ideal moment to put strong domain and DNS hygiene in place instead of carrying legacy risks forward.

Conclusion: Turn Subdomain Takeover into a Solved Problem

Subdomain takeover and orphaned DNS records are not exotic vulnerabilities – they are the natural by‑product of real‑world growth, experiments, SaaS usage and team changes. The good news is that they can be turned into a mostly solved problem with the right habits: a reliable DNS inventory, clear ownership of subdomains, disciplined decommission processes, and sensible security settings around cookies, origins and registrar access.

From a business point of view, treating DNS as part of your core security and SEO strategy pays off quickly. You avoid phishing pages hiding under your brand, protect hard‑won rankings from spam penalties, and keep users from seeing browser or antivirus warnings associated with your domain. For many organisations, a half‑day audit followed by a short clean‑up sprint already removes dozens of unnecessary records and closes obvious takeover opportunities.

If you would like to review your current setup or design a safer architecture for upcoming projects, our team at dchost.com is ready to help – whether you are running a single corporate website, a portfolio of brands, or a multi‑tenant SaaS on VPS, dedicated servers or colocation. Start by listing your domains and DNS providers, and turn this often‑ignored layer into a well‑managed part of your hosting stack.