Networking / Beginners

DNS Fields

Different DNS fields can disclose information to attackers. For example, any host listed in the MX field runs a mail server on port 25/TCP. Similarly, hosts listed in the NS field run DNS servers. Although less common today, the HINFO field is intended to store host information. This may include operating system, architecture, or contact information. Finally, the TXT field is used for generic comments. This information may provide additional insight for an attacker.

Information Hiding

Each piece of DNS information is associated with a 2-byte type field. NS, MX, and TXT are three of the 65,536 possible values (they are 2, 15, and 16, respectively) [RFC1035]. Because new types may be defined in the future, many DNS servers permit caching unknown field types. These undefined fields can be used to store covert information-only clients that know to ask for the information will receive it.

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In this tutorial:

  1. Domain Name System (DNS)
  2. DNS Common Uses
  3. Hostname-to-Address Mapping
  4. Common Lookup Tools
  5. Naming Confusion Attack Vectors
  6. Dotted Names
  7. Name Formatting
  8. Exploited Anonymity
  9. Mail Servers
  10. Sender Policy Framework Overloading
  11. Domain Keys Overloading
  12. DNS Protocol
  13. Packet Information
  14. Simple DNS Server
  15. Distributed Architecture
  16. Top Level Domain Servers
  17. Generic Top Level Domain (gTLD)
  18. Secondary Level Domain (SLD)
  19. Primary and Secondary Servers
  20. Caching Servers
  21. DNS Management
  22. DNS Direct Risks
  23. DNS Performance versus Security
  24. DNS Cache Poisoning
  25. Corrupt DNS Packets
  26. DNS Domain Hijacking
  27. DNS Server Hijacking
  28. Dynamic DNS
  29. Similar Hostnames
  30. Domain Renewals
  31. Hostnames
  32. Zone Transfers
  33. Host Listing
  34. DNS Fields
  35. Mitgation Option
  36. Technical Threat Mitigation
  37. Social Threat Mitigation
  38. Defining Trusted Replies