A Dnsmasq security update has been released for Ubuntu Linux 18.04 LTS, 20.04 LTS, 20.10, and 21.04.

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Ubuntu Security Notice USN-4976-1
June 02, 2021

dnsmasq vulnerability
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 21.04
- Ubuntu 20.10
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS

Summary:

Dnsmasq could be exposed to cache poisoning.

Software Description:
- dnsmasq: Small caching DNS proxy and DHCP/TFTP server

Details:

Petr Mensik discovered that Dnsmasq incorrectly randomized source ports in
certain configurations. A remote attacker could possibly use this issue to
facilitate DNS cache poisoning attacks.

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 21.04:
dnsmasq 2.84-1ubuntu2.1
dnsmasq-base 2.84-1ubuntu2.1
dnsmasq-utils 2.84-1ubuntu2.1

Ubuntu 20.10:
dnsmasq 2.82-1ubuntu1.3
dnsmasq-base 2.82-1ubuntu1.3
dnsmasq-utils 2.82-1ubuntu1.3

Ubuntu 20.04 LTS:
dnsmasq 2.80-1.1ubuntu1.4
dnsmasq-base 2.80-1.1ubuntu1.4
dnsmasq-utils 2.80-1.1ubuntu1.4

Ubuntu 18.04 LTS:
dnsmasq 2.79-1ubuntu0.4
dnsmasq-base 2.79-1ubuntu0.4
dnsmasq-utils 2.79-1ubuntu0.4

After a standard system update you need to reboot your computer to make
all the necessary changes.

References:
  https://ubuntu.com/security/notices/USN-4976-1
CVE-2021-3448

Package Information:
  https://launchpad.net/ubuntu/+source/dnsmasq/2.84-1ubuntu2.1
  https://launchpad.net/ubuntu/+source/dnsmasq/2.82-1ubuntu1.3
  https://launchpad.net/ubuntu/+source/dnsmasq/2.80-1.1ubuntu1.4
  https://launchpad.net/ubuntu/+source/dnsmasq/2.79-1ubuntu0.4