DNS (Domain Name System) is the internet's address book—and a critical attack surface. Attackers exploit DNS for phishing, malware distribution, and data exfiltration. Security professionals use DNS intelligence to detect threats, investigate incidents, and protect their organizations.
DNS Security Fundamentals
DNS translates domain names to IP addresses, making it essential infrastructure—and a prime target.
Common DNS Attacks
| Attack | Description | Impact |
|---|---|---|
| DNS Poisoning | Inject false records into DNS cache | Redirect users to malicious sites |
| DNS Hijacking | Take control of DNS settings | Full traffic interception |
| DNS Tunneling | Encode data in DNS queries | Data exfiltration, C2 communication |
| Typosquatting | Register similar domain names | Phishing, credential theft |
| DNS Amplification | Abuse DNS for DDoS | Service disruption |
📚 DNS Poisoning Explained: How cache poisoning attacks work and how to defend against them.
DNS Security Controls
1. DNSSEC (DNS Security Extensions)
- Cryptographically signs DNS records
- Validates record authenticity
- Prevents cache poisoning
2. DNS Filtering
- Block known malicious domains
- Prevent access to threat categories
- Log DNS queries for analysis
3. Encrypted DNS
- DNS over HTTPS (DoH)
- DNS over TLS (DoT)
- Prevents eavesdropping on queries
Domain Monitoring for Security
Proactive domain monitoring detects threats before they impact your organization.
📚 Monitor Domains for Security Threats: Setting up effective domain monitoring.
What to Monitor
Your domains:
- DNS record changes
- Certificate issuance
- Expiration dates
- Nameserver modifications
Threat domains:
- Lookalike domains (typosquatting)
- Newly registered domains in your space
- Domains referencing your brand
- Phishing infrastructure
Monitoring Approaches
- Certificate Transparency logs
- Passive DNS databases
- Domain registration feeds
- Brand monitoring services
WHOIS for Security Investigations
WHOIS data provides valuable intelligence for threat investigations and due diligence.
Useful WHOIS Fields
| Field | Security Value |
|---|---|
| Registration Date | New domains are higher risk |
| Registrar | Some registrars attract abuse |
| Nameservers | Shared infrastructure patterns |
| Contact Info | Threat actor attribution |
| Domain Status | Suspended domains indicate abuse |
📚 Interpreting WHOIS Dates for Security: What registration and update dates reveal.
WHOIS Resources
- WHOIS Accuracy and Limitations - Understanding data quality
- WHOIS Privacy and GDPR - Privacy impact on investigations
- WHOIS Lookup Tool - Query domain registration data
Certificate Transparency for Discovery
Certificate Transparency (CT) logs record all issued SSL certificates—providing a goldmine for subdomain discovery.
📚 Subdomain Discovery via Certificate Transparency: Leveraging CT logs for reconnaissance.
CT Log Use Cases
Defensive:
- Discover unknown subdomains in your infrastructure
- Detect unauthorized certificate issuance
- Monitor for brand abuse in certificates
Offensive (authorized testing):
- Map target infrastructure
- Find forgotten/legacy systems
- Identify development environments
CT Monitoring Tools
- crt.sh - Free CT log search
- Censys - Certificate and host search
- Certstream - Real-time CT monitoring
Email Security DNS Records
DNS plays a critical role in email security through authentication records.
Essential Email DNS Records
SPF (Sender Policy Framework)
- Lists authorized mail servers
- Prevents spoofing of your domain
DKIM (DomainKeys Identified Mail)
- Cryptographic email signatures
- Verifies message integrity
DMARC (Domain-based Message Authentication)
- Policy for handling auth failures
- Reporting on email abuse
📚 DNS Lookup and Email Security: Verifying email security configuration.
DNS in Threat Intelligence
DNS data enriches threat intelligence:
Passive DNS:
- Historical DNS resolutions
- Domain-to-IP relationships over time
- Infrastructure pattern analysis
DNS Reputation:
- Domain age and history
- Associated malware families
- Threat actor attribution
Fast Flux Detection:
- Rapidly changing DNS records
- Indicates botnet infrastructure
- Bulletproof hosting patterns
Tools for DNS and Domain Security
| Tool | Purpose |
|---|---|
| DNS Lookup | Query DNS records (A, MX, TXT, etc.) |
| WHOIS Lookup | Domain registration information |
| Email Security Checker | Verify SPF, DKIM, DMARC |
Best Practices
For Your Domains
- Enable DNSSEC on all domains
- Monitor CT logs for certificate issuance
- Set calendar reminders for domain renewals
- Use registrar lock to prevent hijacking
- Implement SPF, DKIM, DMARC for email
- Register common typosquats defensively
For Threat Analysis
- Check domain age - new domains are suspicious
- Analyze registration patterns - bulk registrations indicate campaigns
- Map infrastructure - shared hosting reveals connections
- Monitor DNS changes - modifications indicate activity
- Cross-reference indicators - combine with other threat intel
Conclusion
DNS and domain intelligence are essential capabilities for modern security teams. Whether you're defending your infrastructure, investigating incidents, or hunting threats, understanding DNS security provides crucial visibility into attacker operations.
Key takeaways:
- Protect your DNS with DNSSEC and monitoring
- Monitor for abuse of your brand and domains
- Use WHOIS and CT logs for investigation and discovery
- Implement email authentication to prevent spoofing
- Leverage DNS intelligence for threat detection
The domain name system is both a critical dependency and a valuable data source. Secure your DNS infrastructure and use DNS intelligence to stay ahead of threats.
