A DHCP security update has been released for Ubuntu Linux 14.04 ESM and 16.04 ESM.

USN-4969-2: DHCP vulnerability

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Ubuntu Security Notice USN-4969-2
May 27, 2021

isc-dhcp vulnerability
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 16.04 ESM
- Ubuntu 14.04 ESM

Summary:

DHCP could be made to crash if it received specially crafted network
traffic.

Software Description:
- isc-dhcp: DHCP server and client

Details:

USN-4969-1 fixed a vulnerability in DHCP. This update provides
the corresponding update for Ubuntu 14.04 ESM and 16.04 ESM.

Original advisory details:

Jon Franklin and Pawel Wieczorkiewicz discovered that DHCP incorrectly
handled lease file parsing. A remote attacker could possibly use this issue
to cause DHCP to crash, resulting in a denial of service.

Update instructions:

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

Ubuntu 16.04 ESM:
isc-dhcp-client 4.3.3-5ubuntu12.10+esm1
isc-dhcp-server 4.3.3-5ubuntu12.10+esm1

Ubuntu 14.04 ESM:
isc-dhcp-client 4.2.4-7ubuntu12.13+esm1
isc-dhcp-server 4.2.4-7ubuntu12.13+esm1

In general, a standard system update will make all the necessary changes.

References:
  https://ubuntu.com/security/notices/USN-4969-2
  https://ubuntu.com/security/notices/USN-4969-1
CVE-2021-25217