If you manage any kind of online presence, you have a digital footprint – and it’s probably larger than you think. Every domain, subdomain, email server, and DNS record creates a trail that can either strengthen your security or become a vulnerability. The problem is, most organizations have no clear picture of what their complete DNS infrastructure actually looks like.
I learned this the hard way a few years ago when I was managing infrastructure for a growing SaaS company. We thought we had a good handle on our domains, but when we finally did a comprehensive audit, we found 47 subdomains we’d forgotten about. Some were old staging environments, others were demo sites created by sales teams, and a few were complete mysteries. Three of them were pointing to services we’d stopped paying for months earlier – a textbook setup for a subdomain takeover attack.
What DNS Infrastructure Mapping Actually Means
DNS infrastructure mapping is the process of discovering and documenting every DNS record associated with your domains. This includes not just the obvious ones like your main website and email servers, but every subdomain, every DNS record type, and every configuration detail that makes up your DNS presence.
Think of it like creating a map of a building. You wouldn’t just draw the front entrance and call it complete – you need to know about every door, window, utility connection, and access point. Your DNS infrastructure works the same way. Every subdomain is a potential entry point, and you need to know they all exist and where they lead.
Why Your Digital Footprint Matters
The size and complexity of your DNS footprint directly impacts your security posture. Here’s what happens in practice: a developer spins up a test environment at test.yourcompany.com, uses it for a week, then moves on to something else. The subdomain sits there, forgotten. Six months later, the cloud service it pointed to gets decommissioned. Now that subdomain points to nothing – or worse, someone else can claim that cloud resource and suddenly they control test.yourcompany.com.
This isn’t theoretical. Subdomain takeover attacks happen constantly because organizations lose track of their DNS records. In 2019, several major companies discovered that attackers had taken over forgotten subdomains and were using them to serve phishing pages or steal session cookies. The attackers didn’t need to breach anything – they just claimed abandoned cloud resources that DNS records still pointed to.
Common Sources of DNS Sprawl
DNS infrastructure tends to grow organically and chaotically. Marketing teams create campaign-specific subdomains. Developers spin up staging environments. Regional offices set up their own services. Partners get their own subdomains for integrations. Each of these makes sense in isolation, but collectively they create a sprawling infrastructure that nobody fully understands.
The worst part is that DNS records are often created and forgotten. Unlike a server that costs money every month and eventually gets noticed in budget reviews, DNS records are essentially free and invisible. That staging.yourcompany.com subdomain from three years ago? It’s still there in your DNS zone, pointing to who-knows-what, and nobody remembers creating it.
How to Map Your DNS Infrastructure
Start by making a list of all domains you own. This sounds obvious, but many organizations have domains registered across multiple accounts, different registrars, and sometimes in the names of people who no longer work there. Get this consolidated first.
For each domain, you need to discover all associated subdomains. This is harder than it sounds because DNS doesn’t work like a directory listing – you can’t just ask a DNS server ”show me all subdomains.” Instead, you need to use subdomain enumeration techniques like DNS brute-forcing, certificate transparency log searches, and historical DNS data.
Once you’ve discovered your subdomains, document where each one points and what it’s used for. This is where the detective work begins. Some will be obvious – mail.yourcompany.com clearly handles email. Others require investigation. That api-staging-temp-201903.yourcompany.com? You’ll need to track down who created it and whether it’s still needed.
Red Flags to Watch For
Pay special attention to subdomains pointing to cloud services. These are the highest risk for takeover attacks. If you see records pointing to AWS S3 buckets, Azure resources, GitHub Pages, or similar services, verify that you still control those resources. Actually log in and check – don’t just assume they’re fine.
Look for DNS records that haven’t been updated in years. Old records often point to services that no longer exist. Check for inconsistent patterns too. If most of your infrastructure is on AWS but you have random subdomains pointing to a different cloud provider, investigate why.
Missing or incorrect security records are another major issue. Your domain should have SPF records to prevent email spoofing, DKIM for email authentication, and DMARC policies to handle failures. Many organizations have these on their main domain but forget to configure them for subdomains that also send email.
Keeping Your Map Current
DNS infrastructure mapping isn’t a one-time project – it needs to be continuous. Your infrastructure changes constantly, and your map needs to reflect those changes. New subdomains get created, old ones should be removed, and configurations need updates.
The only practical way to handle this is automation. Manual checking doesn’t scale and won’t catch changes in real-time. You need systems that continuously scan your DNS infrastructure, alert you to changes, and flag potential security issues before they become problems.
Set up alerts for specific scenarios: new subdomains appearing, existing subdomains starting to point to different locations, DNS records pointing to services that no longer respond, or security records becoming misconfigured. These alerts let you catch issues immediately instead of discovering them during your next manual audit.
The Real Cost of Not Knowing
Organizations that don’t understand their DNS footprint face concrete risks. Beyond subdomain takeovers, there’s the operational chaos of not knowing what infrastructure you actually have. Teams waste time troubleshooting DNS issues because nobody knows the full picture. Security audits take longer and cost more because the infrastructure has to be discovered before it can be assessed.
There’s also the reputation risk. If attackers take over a forgotten subdomain and use it for phishing or malware distribution, that’s your domain name in the browser bar. Even if the subdomain itself was abandoned, you’ll be the one explaining to customers and partners why yourcompany.com appeared in a phishing attack.
Knowing your complete DNS footprint isn’t optional anymore – it’s a basic security requirement. The good news is that with the right approach and tools, it’s entirely manageable. Start with discovery, maintain continuous monitoring, and treat your DNS infrastructure as the critical security boundary that it actually is.