We are pleased to announce the release of version 1.21.1 of the Unboundrecursive DNS resolver.

This security release fixes CVE-2024-8508.

A vulnerability has been discovered in Unbound when handling replieswith very large RRsets that Unbound needs to perform name compressionfor.

Malicious upstreams responses with very large RRsets can cause Unboundto spend a considerable time applying name compression to downstreamreplies. This can lead to degraded performance and eventually denial ofservice in well orchestrated attacks.

Unbound version 1.21.1 introduces a hard limit on the number of namecompression calculations it is willing to do per packet.Packets that need more compression will result in semi-compressedpackets or truncated packets, even on TCP for huge messages, to avoidlocking the CPU for long.

This change should not affect normal DNS traffic.

We would like to thank Toshifumi Sakaguchi for discovering andresponsibly disclosing the vulnerability.