unbound-1.6.6-5.0.2.el7.AXS7

Unbound is a validating, recursive, and caching DNS(SEC) resolver.

The C implementation of Unbound is developed and maintained by NLnet Labs. It is
based on ideas and algorithms taken from a java prototype developed by Verisign
labs, Nominet, Kirei and ep.net.

Unbound is designed as a set of modular components, so that also DNSSEC (secure
DNS) validation and stub-resolvers (that do not run as a server, but are linked
into an application) are easily possible.

Security Fix(es):

* CVE-2022-3204: add max number of lookups in the cache for target nameserver
names

CVE(s):
CVE-2022-3204
A vulnerability named 'Non-Responsive Delegation Attack' (NRDelegation Attack) has been discovered in various DNS resolving software. The NRDelegation Attack works by having a malicious delegation with a considerable number of non responsive nameservers. The attack starts by querying a resolver for a record that relies on those unresponsive nameservers. The attack can cause a resolver to spend a lot of time/resources resolving records under a malicious delegation point where a considerable number of unresponsive NS records reside. It can trigger high CPU usage in some resolver implementations that continually look in the cache for resolved NS records in that delegation. This can lead to degraded performance and eventually denial of service in orchestrated attacks. Unbound does not suffer from high CPU usage, but resources are still needed for resolving the malicious delegation. Unbound will keep trying to resolve the record until hard limits are reached. Based on the nature of the attack and the replies, different limits could be reached. From version 1.16.3 on, Unbound introduces fixes for better performance when under load, by cutting opportunistic queries for nameserver discovery and DNSKEY prefetching and limiting the number of times a delegation point can issue a cache lookup for missing records.