SAD DNS Explained - Defeating Source Port Randomization with Fragmentation

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JulioHM

JulioHM

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Oct 25, 2020
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SAD DNS Explained
blog.cloudflare.com

SAD DNS Explained

Researchers from UC Riverside and Tsinghua University found a new way to revive a decade-old DNS cache poisoning attack. Read our deep dive into how the SAD DNS attack on DNS resolvers works, how we protect against this attack in 1.1.1.1, and what the future holds for DNS cache poisoning attacks.
blog.cloudflare.com blog.cloudflare.com

The recent UDP feature of packet fragmentation has brought back to life an old DNS attack that was previously mitigated by port randomization.

As is often the case in computer security, old attacks become new again when attackers discover new capabilities. In 2012, researchers Amir Herzberg and Haya Schulman from Bar Ilan University discovered that it was possible for a remote attacker to defeat the protections provided by source port randomization. This new attack leveraged another feature of UDP: fragmentation. For a primer on the topic of UDP fragmentation, check out our previous blog post on the subject by Marek Majkowski.
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