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Recursive DNS Cache Auditing

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  1. Recursive DNS Cache Auditing • Jose Avila III • Founder, ONZRA

  2. Who Am I? • One of the founders of ONZRA • Security Researcher • Previous Lead Developer at NeuStar for the Managed Internal DNS and SiteBacker2 products

  3. Cache Poisoning Is Not New! • We find out we were poisoned when services start failing! • There is a need for a notification system • Why aren’t there solutions to detect this?

  4. Where Does ONZRA Fit In? • Developing a Cache Verification Tool • Verifies changes seen in cache • Alert on potential Cache Poisoning Events • Similar to DoX concept

  5. How Does It Work? • Takes a dump of the in-memory cache • Finds differences with an old dump • Verifies the changes • Checks authoritative servers • Checks peer recursive servers • Alerts if results could not be verified

  6. Features • Recordset comparison • Content Delivery Network detection • Record type based comparison • Threshold based peer approval • History tracking • Alerting based on percentage of change

  7. Content Delivery Network Detection • Detected by comparing the record sets amongst the peers • Can lower the alert level

  8. Record Comparison • Ordering of records does not matter • We don’t have to verify everything • What we do not verify: • MX Record: Preference • SOA Record: Serial, etc.

  9. Threshold Based Peer Approval • Based on the threshold of required peers we need to alter our probing interval. • If too much time passes we will not be able to verify with peers

  10. Probe Interval • Verify Freq. = TTL-(THRESHxTTL/PEERS) • Verifying against: • 20 Peers • 10% Threshold • 120s Min TTL • Need to verify cache every 108 seconds

  11. History Tracking • Stores a history of prior record sets • If the record is not verified by peers its verified against historic values

  12. Detecting Fast Flux • Value changing quicker than the TTL • Peers will have multiple values represented • Screws up prior formula • How can we verify these? • Shared DB of historic data?

  13. Tool Components • TCP Daemon (Listens for Cache Dumps) • Cache Dump Parsers • Cache Compare • Application Cache • CDN / Fast Flux Detection • Alerter (Currently only SYSLOG)

  14. What Resolvers Are Supported? • Currently Supported • Microsoft DNS • Bind • Supported eventually • DJB DNS w/ custom Patch • PowerDNS

  15. Future Features • Cache Verification Service? • More Research Data • Multiple Query Nodes • Better CDN Detection • Use peer cache dumps instead of querying • Interaction with other DNS Projects

  16. Questions? Jose.Avila@ONZRA.com Keith.Myers@ONZRA.com

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