The CVE number for this vulnerability is 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.


== Summary
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.

Unbound 1.21.1 includes a fix to limit time spent on name compression.


== Affected products
Unbound up to and including 1.21.0.


== Description
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.


== Solution
Apply the attached patch using:

     patch -p1 < patch_CVE-2024-8508.diff

then run 'make install' to install Unbound.

The patch is tested to work on Unbound 1.21.0.


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