Unbound 1.21.1

This security release fixes CVE-2024-8508.

A vulnerability has been discovered in Unbound when handling replies
with very large RRsets that Unbound needs to perform name compression
for.

Malicious upstreams responses with very large RRsets can cause Unbound
to spend a considerable time applying name compression to downstream
replies. This can lead to degraded performance and eventually denial of
service in well orchestrated attacks.

The vulnerability can be exploited by a malicious actor querying Unbound
for the specially crafted contents of a malicious zone with very large
RRsets.
Before Unbound replies to the query it will try to apply name
compression which was an unbounded operation that could lock the CPU
until the whole packet was complete.

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

This change should not affect normal DNS traffic.

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

Bug Fixes:

• Fix CVE-2024-8508, unbounded name compression could lead to denial of
  service.