Dynamic DNS

Hunt Hypothesis

Adversaries may use dynamic DNS to maintain persistent,隐蔽 communication channels, allowing them to evade traditional network monitoring. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify potential command and control infrastructure and disrupt ongoing malicious activities.

YARA Rule

rule dyndns {
    meta:
        author = "x0r"
        description = "Dynamic DNS"
	version = "0.1"
    strings:
        $s1 = "SOFTWARE\\Vitalwerks\\DUC" nocase
    condition:
        any of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Scheduled DNS Update for Cloud Infrastructure
  Description: A cloud provider’s management tool (e.g., AWS Route 53, Azure DNS) automatically updates DNS records for load balancing or scaling.
  Filter/Exclusion: Check for known cloud provider IP ranges or use a filter like src_ip IN (cloud_provider_dns_servers).

• Scenario: DNS Server Maintenance Task
  Description: An administrator runs a DNS server maintenance script (e.g., nsupdate, named-checkzone) to refresh or validate zone files.
  Filter/Exclusion: Use a filter like process_name NOT IN ("nsupdate", "named-checkzone") or check for known admin user accounts.

• Scenario: Internal DNS Monitoring Tool
  Description: A company’s internal DNS monitoring tool (e.g., dnsmasq, PowerDNS) periodically checks DNS records for consistency.
  Filter/Exclusion: Filter by process_name or src_ip to exclude internal monitoring tools.

• Scenario: DNS-based Load Balancer Configuration
  Description: A load balancer (e.g., HAProxy, NGINX) updates DNS records to direct traffic to different backend servers.
  Filter/Exclusion: Use a filter like process_name NOT IN ("haproxy", "nginx") or check for known load balancer IP ranges.

• Scenario: User-Initiated DNS Change via GUI
  Description: An admin manually updates DNS settings via a GUI tool (e.g., DNS Manager on Windows Server) for a specific host.
  Filter/Exclusion: Filter by user_account (e.g., admin_user) or check for process_name like dnsmgmt.msc.