Passive DNS

Passive DNS is a system that records DNS (Domain Name System) data as it occurs in real-time, without actively querying DNS servers itself. Instead of a system asking "What is the IP address for example.com?", Passive DNS listens to the responses from DNS servers to those queries from other systems.

Here's a breakdown of the key elements:

• Data Collection: Passive DNS systems collect and store DNS records (like A, AAAA, MX, NS records) and their associated metadata (like timestamps) as they are transmitted across the network.

• Historical Record: This creates a historical database of DNS resolutions, allowing security analysts to look back in time and see how DNS records have changed.

• No Active Queries: Passive DNS operates by "passively" observing network traffic, so it does not generate DNS queries itself, making it harder for malicious actors to detect its operation.

• Forensic Analysis: It is used extensively in forensic investigations to:

  • Track the history of domain names and IP addresses.

  • Identify connections between malicious domains and infrastructure.

  • Establish timelines of attacker activity.

• Threat Detection: Passive DNS data is used for threat detection to:

  • Identify potentially malicious domains or IP addresses.

  • Detect patterns of suspicious DNS activity.

  • Correlate DNS data with other security events.

Passive DNS provides a valuable historical record of DNS activity that can be used to investigate security incidents, detect malicious activity, and gain a deeper understanding of network infrastructure.

ThreatNG has features that strongly complement and use information similar to Passive DNS. Here's how:

1. External Discovery: Mapping the Landscape

• ThreatNG's external discovery is similar to the initial data collection phase of understanding DNS.

• An organization's external-facing assets are identified by performing unauthenticated discovery, which inherently involves looking at domain names and related information.

• This sets the stage for the more detailed DNS analysis that ThreatNG performs.

2. External Assessment: Deep Dive into DNS

• ThreatNG's external assessment capabilities include very detailed DNS intelligence:

  • DNS Intelligence: ThreatNG has "DNS Intelligence capabilities which include Domain Name Permutations and Web3 Domains that are available and taken". It uses "Domain Intelligence (Enumeration of Vendor Technologies from DNS and Subdomains)".

  • This goes beyond simple resolution and looks at related domains, a technique often used with Passive DNS to uncover malicious infrastructure.

  • Domain Record Analysis: ThreatNG performs "Domain Record Analysis (IP Identification, Vendors and Technology Identification)". This is a core function of Passive DNS – seeing the records and how they change.

  • Subdomain Intelligence: ThreatNG's "Subdomain Intelligence (HTTP Responses, Header Analysis (Security Headers and Deprecated Headers), Server Headers (Technologies), Cloud Hosting...Subdomain Takeover Susceptibility, Content Identification...Ports (IoT / OT...Databases...Remote Access Services), Known Vulnerabilities, Web Application Firewall Discovery and Vendor Types)" uses DNS data to understand an organization's attack surface.

• Essentially, ThreatNG actively queries DNS to build its picture, but it analyzes the results very similarly to how Passive DNS is used.

3. Reporting: Highlighting DNS-Related Risks

• ThreatNG's reporting can highlight risks directly related to DNS configurations.

• For example, it can report on subdomains vulnerable to takeover, a finding that relies heavily on DNS data analysis.

4. Continuous Monitoring: Tracking DNS Changes

• ThreatNG's continuous monitoring of the external attack surface implicitly involves tracking changes in DNS records.

• While it may not store the entire history like a Passive DNS system, it detects when key records change, which is crucial for security.

5. Investigation Modules: Powerful DNS Tools

• ThreatNG's investigation modules provide tools to analyze DNS data in detail:

  • The Domain Intelligence module is packed with DNS capabilities, as described above.

6. Intelligence Repositories: Contextualizing DNS

• ThreatNG's intelligence repositories provide context that makes DNS analysis more effective.

  • For example, knowing about known malicious domains helps prioritize DNS findings.

7. Working with Complementary Solutions

• This is where ThreatNG truly shines concerning Passive DNS. It's designed to work with other security data:

  • SIEM Systems: You could feed ThreatNG's DNS findings (e.g., vulnerable subdomains) into a SIEM, and correlate it with Passive DNS data from a dedicated system to get a much richer picture of an attack.

  • Threat Intelligence Platforms: Correlating ThreatNG's active DNS scans with Passive DNS data helps identify malicious infrastructure faster.

• For example, imagine ThreatNG finds a new subdomain. A security analyst could then use a Passive DNS database to see the history of that subdomain's IP address, revealing if it was previously used for malicious activity.

In summary, while ThreatNG is not a Passive DNS system itself, it uses DNS data extensively, and its capabilities are greatly enhanced by integration with Passive DNS data from other sources.