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Avoiding dns amplification attacks

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Avoiding dns amplification attacks

  1. 1. Avoiding DNS amplification attacks
  2. 2. Who am I?  @deassain  Security Advisor at a Big 4 company  contributor 
  3. 3. What is DNS amplification?  Distributed Denial of Service Attack  Abusing flaw in the DNS protocol's architecture  Spamhaus 300 Gbit/s
  4. 4. Reasons  DNS request vs DNS response (UDP)  Open resolving name servers  No implementation of BCP38
  5. 5. DNS Request vs Response Size  30 byte request → up to 500 byte response  1 Mbit on your machine → 17 Mbit at the target machine  Amplification
  6. 6. Open resolvers  Resolves DNS queries for any host  Spoof UDP source to target IP address  Tons of DNS responses end up at the target  Get your machines and disable recursion from the internet! (or the crypto bear will kick your ass )
  7. 7. BCP38: Ingres Filtering  Works for IPv4   Upstream providers only allow traffic for IP blocks for which their clients are configured  Cooperation between ISPs