If the Internet were a gigantic city, the DNS would be its address system, its phone book, and at the same time, one of its biggest points of control. Although almost no one sees it and few think about it on a daily basis, nothing on the Internet works without DNS. And precisely for this reason, it is also one of the favorite attack vectors.

In this article we are going to explore the world of DNS from scratch, but with a cybersecurity mentality: what it is, how it works, what it is used for, how it is integrated into real environments, what risks it has, and how to protect it correctly.

DNS (Domain Name System) is the system that translates human-readable names into machine-readable IP addresses.

In simple terms:

DNS converts www.ejemplo.com to 142.250.72.196

Humans remember names. Computers communicate with numbers. DNS is the universal translator between both worlds.

Without DNS, each user would have to memorize IP addresses to access any service. The Internet, as we know it, would be impracticable.

When you type a URL into your browser, a string of events occurs that typically lasts milliseconds:

1. The operating system checks your local DNS cache.
2. If there is no response, query when resolving configured DNS (ISP, enterprise, public provider).
3. Solving questions to:
   • Root Servers
   • TLD servers (.com, .net, .org, etc.)
   • Authoritative domain server
4. The returned IP is cached.
5. The browser already knows which server to connect to.

This entire process happens before HTTPS, authentication, or data exchange exists. That’s why, if the DNS is compromised, everything else can be compromised as well.

Although many associate it with just “entering a web page,” DNS is critical for multiple functions:

• Web browsing (HTTP / HTTPS)
• Sending and receiving emails (MX records)
• Cloud Services
• Microservices and containers
• Authentication and federation
• Load balancing
• Geographic failover
• VPNs and Remote Access
• Active Directory and corporate environments

In enterprise environments, DNS is a silent dependency: no one notices it until it fails.

DNS is attractive to attackers for three key reasons:

1. It’s everywhere
2. It is reliable by design
3. Historically it was poorly protected

DNS is trusted by design… and that is precisely why it is so exploited. Below we discuss the most common attacks and, most importantly, how to mitigate them with current technologies.

Poisoning the truth

What does it consist of?

The attacker pushes fake DNS responses into a resolver’s cache, so that future legitimate queries resolve to malicious IP addresses.

The user types in the correct URL, but ends up on the attacker’s server.

How it operates

• DNS Response Forgery
• Leverage misconfigured resolvers
• Race attacks (respond before the legitimate server)
• Exploiting lack of cryptographic validation

Impact

• Stealth phishing
• Credential theft
• Malware distribution
• Massive user engagement

How to protect yourself

• Enable DNSSEC
• Using resolvers that validate signatures
• Avoid open resolvers
• Minimize excessive time-to-live (TTL)
• Segmentation of internal resolvers

Technologies/Tools

• DNSSEC
• BIND with validation
• Unbound
• PowerDNS
• Cisco Umbrella
• Cloudflare DNS
• Route 53 + DNSSEC

When they change your GPS without you noticing it

What does it consist of?

The attacker modifies the DNS settings in:

• Routers
• End teams
• Authoritative Servers
• Domain Dashboards

All traffic is resolved by servers controlled by the attacker.

How it operates

• Weak credentials
• Vulnerable home routers
• Commit Accounts to Register
• Malware that changes local DNS

Impact

• Total traffic redirection
• Persistent phishing
• Loss of domain control
• Interception of communications

How to protect yourself

• Multi-factor authentication in registrars
• DNS Change Monitoring
• Endpoints with protection against unauthorized changes
• Blocking unprivileged network modifications
• Zero Trust DNS

Technologies/Tools

• MFA in registrars (GoDaddy, Namecheap, etc.)
• EDR (CrowdStrike, Defender)
• Cisco Umbrella Roaming Client
• Cloudflare Registrar + DNS Lock
• SIEM with DNS Change Alerts

Intercepting the conversation from the start

What does it consist of?

The attacker positions itself between the client and the DNS resolver, intercepting and manipulating queries.

How it operates

• Open Wi-Fi networks
• ARP poisoning
• DHCP spoofing
• Unencrypted DNS (UDP/53)

Impact

• Silent redirection
• Session Capture
• HTTPS degradation
• Attacks combined with SSL stripping

How to protect yourself

• DNS encryption
• Avoid Flat DNS
• Using Corporate VPN
• Strict network policies

Technologies/Tools

• DNS over HTTPS (DoH)
• DNS over TLS (DoT)
• Cloudflare 1.1.1.1
• Google DoH
• Cisco Umbrella + DoH
• ZTNA (Zscaler, Cloudflare Zero Trust)

Exfiltration hidden in seemingly innocent queries

What does it consist of?

Using DNS queries to:

• Exfiltrate data
• Create command-and-control channels
• Bypassing traditional firewalls

The data travels encoded within domain names.

How it operates

• Long and random subdomains
• High entropy
• Frequently Asked Questions
• Using TXT Records

Impact

• Information theft
• Malware persistence
• Bypass of perimeter controls
• Difficulty of detection

How to protect yourself

• DNS Behavioral Analysis
• Entropy Detection
• Limit query length
• Blocking suspicious domains

Technologies/Tools

• Cisco Umbrella
• Infoblox BloxOne Threat Defense
• Palo Alto DNS Security
• Azure Defender for DNS
• SIEM + UEBA
• Zeek / Meerkat

Lots of traffic with little effort

What does it consist of?

The attacker uses open DNS servers to amplify traffic to a victim.

A small query generates a much larger response.

How it operates

• Misconfigured open DNS
• IP spoofing
• Reflection attacks
• Using ANY queries

Impact

• Network saturation
• Drop in services
• Economic losses
• Reputational damage

How to protect yourself

• Close open resolvers
• Rate limiting
• Disable ANY queries
• DDoS Mitigation Services

Technologies/Tools

• Cloudflare DDoS Protection
• AWS Shield
• Azure DDoS Protection
• Akamai
• BIND rate-limiting
• Firewalls L7

The deception begins before the mail

What does it consist of?

Creation of malicious domains visually similar to legitimate ones, combined with valid DNS resolutions.

How it operates

• Typosquatting
• Homoglyph attacks
• Newly registered domains
• Ephemeral infrastructure

Impact

• Credential theft
• Account Compromise
• Financial fraud
• Initial accesses for major attacks

How to protect yourself

• Locking newly created domains
• Threat intelligence
• Policies by category
• User Awareness

Technologies/Tools

• Cisco Umbrella
• Proofpoint DNS
• Quad9
• Microsoft Defender for DNS
• Secure Web Gateways
• DMARC + SPF + DKIM (Supplemental)

Malware that speaks softly

What does it consist of?

The malware uses DNS as a channel for:

• Communication
• Update
• Receiving Commands

Avoid detection because DNS is usually allowed.

How it operates

• Regular consultations
• Algorithmically generated domains (DGA)
• Using TXT records
• Distributed Infrastructure

Impact

• Prolonged persistence
• Remote control of systems
• Lateral movement
• Data exfiltration

How to protect yourself

• DGA Detection
• DNS Pattern Analysis
• Automatic locking
• DNS + EDR integration

Technologies/Tools

• Cisco Umbrella
• CrowdStrike Falcon
• Microsoft Defender XDR
• Cortex XDR High Stick
• SIEM + Threat Intelligence
• SOAR for autoresponder

For years, DNS was seen as a “neutral” service. Today it is a key defensive tool.

Modern security controls over DNS

• DNS Filtering (blocking malicious domains)
• Built-in Threat Intelligence
• DNSSEC (cryptographic signed)
• Logging and visibility
• C2 Lock
• Data exfiltration prevention
• Zero Trust DNS

In many environments, DNS is the first line of defense, even before the firewall.

Well-known public providers

Supplier	DNS	Security	Approach
Google	8.8.8.8	Basic	Performance
Cloudflare	1.1.1.1	Media	Privacy
OpenDNS (Cisco Umbrella)	Yes	High	Enterprise Security
Quad9	9.9.9.9	Medium–High	Blocking malware
AWS Route 53	Yes	High	Cloud / Infrastructure
Azure DNS	Yes	High	Microsoft Integration

Key Differences

• Google: fast, but little security control.
• Cloudflare: Focus on privacy and speed.
• Umbrella: threat intelligence, policies, visibility.
• Route 53 / Azure DNS: Ideal for cloud and automation.

The choice depends on whether you’re looking for speed, security,  or enterprise control.

On a personal computer

• Configured at the operating system level
• It can aim at:
  • ISP
  • Public DNS
  • Corporate DNS
  • Security DNS

In a company

• Internal DNS + External DNS
• Split-horizon DNS
• Active Directory Integration
• Policies by user or network
• Centralized logging

In the cloud

• DNS as Code
• High availability
• CI/CD Integration
• Intelligent routing

Today, DNS doesn’t live alone. Integrates with:

• ALWAYS
• SOAR
• EDR/XDR
• Next-generation firewalls
• CASB
• ZTNA
• Identity Platforms

Real example:

An infected endpoint attempts to resolve a C2 domain →DNS blocks it → generates an alert → SOAR isolates the computer → SOC investigates.

It all starts with a simple DNS query.

Example 1: Secure DNS for users

• Solve: Cisco Umbrella
• Policies:
  • Malware blocking
  • Phishing blocking
  • Categories by role
• Logging enabled

Example 2: Hybrid corporate DNS

• Internal DNS: Active Directory
• Forwarders:
  • Resolve External Insurance
• DNSSEC enabled
• Continuous monitoring

Example 3: Cloud DNS

• Route 53
• Automated Registrations
• Health checks
• Cross-region failover

For a long time, DNS was treated as a basic service. Today, DNS is a strategic layer of security, visibility, and control.

Who understands DNS:

• Improve your security posture
• Detect attacks earlier
• Reduces exhibition surface
• Gain control over your traffic

In cybersecurity, the invisible is often the most critical. And DNS is, without a doubt, one of the best examples.

Thanks for reading me!!