Passive DNS Monitoring

Passive DNS monitoring enables the firewall to act as a passive DNS sensor and send DNS information to Palo Alto Networks for analysis to improve threat intelligence and threat prevention capabilities. The data collected includes non-recursive DNS query (that is, the web browser sends a query to a DNS server to translate a domain to an IP address, and the server returns a response without querying other DNS servers) and response packet payloads. See DNS Overview for more background information about DNS.
The threat intelligence that the firewall collects from passive DNS monitoring consists solely of domain-to-IP address mappings. Palo Alto Networks retains no record of the source of this data and does not have the ability to associate it with the submitter at a future date. The Palo Alto Networks threat research team uses passive DNS information to gain insight into malware propagation and evasion techniques that abuse the DNS system. Information gathered through this data collection is used to improve PAN-DB URL category and DNS-based C2 signature accuracy and WildFire malware detection.
The firewall forwards DNS responses only when the following requirements are met:
  • DNS response bit is set
  • DNS truncated bit is not set
  • DNS recursive bit is not set
  • DNS response code is 0 or 3 (NX)
  • DNS question count bigger than 0
  • DNS Answer RR count is bigger than 0 or if it is 0, the flags need to be 3 (NX)
  • DNS query record type are A, NS, CNAME, AAAA, MX

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