dnsmasq vulnerabilities

USN-6657-1 fixed several vulnerabilities in Dnsmasq. This update provides
the corresponding update for Ubuntu 16.04 LTS and Ubuntu 18.04 LTS.

Original advisory details:

Elias Heftrig, Haya Schulmann, Niklas Vogel, and Michael Waidner discovered
that Dnsmasq icorrectly handled validating DNSSEC messages. A remote
attacker could possibly use this issue to cause Dnsmasq to consume
resources, leading to a denial of service. (CVE-2023-50387)

It was discovered that Dnsmasq incorrectly handled preparing an NSEC3
closest encloser proof. A remote attacker could possibly use this issue to
cause Dnsmasq to consume resources, leading to a denial of service.
(CVE-2023-50868)

It was discovered that Dnsmasq incorrectly set the maximum EDNS.0 UDP
packet size as required by DNS Flag Day 2020. This issue only affected
Ubuntu 23.10. (CVE-2023-28450)