How to Detect and Analyze Suspicious Domain Name Resolution Requests in DNS Logs

Suspicious DNS activity can indicate malicious behavior, such as command-and-control (C2) communication, data exfiltration, or malware activity. Detecting such activity involves monitoring DNS logs for anomalies and correlating them with threat intelligence.

---

1. Monitor for High Frequency of DNS Queries

What to Look For:

• Query Volumes:

  • High-frequency queries to specific domains or IPs, especially those not commonly accessed.

• Patterns:

  • Repeated queries to newly registered domains or domains associated with suspicious activity.

• Potential Indicators:

  • Command-and-control (C2) communication or data exfiltration.

Red Flags: Unusual spikes in DNS queries from specific hosts or targeting uncommon domains.

---

2. Check for Suspicious or Malformed Domain Names

What to Look For:

• Domain Characteristics:

  • Long, random-looking domain names.

  • Domains associated with typosquatting (e.g., g00gle.com instead of google.com).

  • Domains with uncommon Top-Level Domains (TLDs), such as .xyz, .pw, or .top.

• Domain Generation Algorithms (DGAs):

  • Automatically generated domain names that appear nonsensical or overly complex.

Red Flags: Queries to domains with odd or unpredictable structures, often used by attackers to evade detection.

---

3. Investigate Nonexistent Domain (NXDOMAIN) Responses

What to Look For:

• NXDOMAIN Patterns:

  • A high number of NXDOMAIN responses for queries originating from the same host.

• Attack Techniques:

  • Attackers cycling through domains generated by DGAs to find active command-and-control servers.

Red Flags: Frequent NXDOMAIN responses, indicating repeated failed attempts to resolve malicious domains.

---

4. Analyze Queries to External DNS Servers

What to Look For:

• External Server Usage:

  • DNS queries sent to unauthorized or external DNS servers, bypassing internal DNS infrastructure.

• Potential Indicators:

  • Malware or attackers attempting to hide activity from internal monitoring.

Red Flags: Unexpected queries to public DNS servers (e.g., 8.8.8.8, 1.1.1.1) or unrecognized external servers.

---

5. Cross-Reference with Threat Intelligence

What to Do:

• Threat Intelligence Feeds:

  • Correlate queried domains against threat intelligence databases for known malicious or suspicious domains.

• Real-Time Integration:

  • Leverage security tools to flag domains with a history of malicious activity.

Red Flags: Domains flagged as malicious by threat intelligence or associated with recent attack campaigns.

---

6. Immediate Response

What to Do:

• Block Malicious Domains:

  • Use firewalls, DNS filtering solutions, or endpoint security tools to block access to the identified domains.

• Investigate Source Hosts:

  • Analyze logs to identify the systems or users responsible for the suspicious DNS queries.

• Notify Relevant Teams:

  • Alert incident response and security teams to investigate and contain the threat.

• Harden DNS Infrastructure:

  • Enforce DNS filtering policies and monitor for further anomalies.

Post-Incident Actions:

• Educate Users:

  • Train staff on recognizing phishing and other tactics that may trigger malicious DNS activity.

• Enhance Monitoring:

  • Deploy real-time DNS monitoring tools to detect and block suspicious queries proactively.

• Review and Update Threat Feeds:

  • Ensure threat intelligence feeds are current and comprehensive.

---

Conclusion

By analyzing DNS logs for high-frequency queries, malformed domain names, and unauthorized external resolutions, organizations can detect and mitigate suspicious activity early. Proactive monitoring, coupled with threat intelligence, ensures a robust defense against DNS-based threats.