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

USN-5062-1: Linux kernel vulnerability

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Ubuntu Security Notice USN-5062-1
September 08, 2021

linux, linux-aws, linux-kvm, linux-lts-xenial 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:

The system could be made to crash or run programs as an administrator.

Software Description:
- linux: Linux kernel
- linux-aws: Linux kernel for Amazon Web Services (AWS) systems
- linux-kvm: Linux kernel for cloud environments
- linux-lts-xenial: Linux hardware enablement kernel from Xenial for Trusty

Details:

Maxim Levitsky discovered that the KVM hypervisor implementation for AMD
processors in the Linux kernel did not properly prevent a guest VM from
enabling AVIC in nested guest VMs. An attacker in a guest VM could use this
to write to portions of the host's physical memory.

Update instructions:

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

Ubuntu 16.04 ESM:
linux-image-4.4.0-1097-kvm 4.4.0-1097.106
linux-image-4.4.0-1132-aws 4.4.0-1132.146
linux-image-4.4.0-214-generic 4.4.0-214.246
linux-image-4.4.0-214-lowlatency 4.4.0-214.246
linux-image-aws 4.4.0.1132.137
linux-image-generic 4.4.0.214.221
linux-image-kvm 4.4.0.1097.95
linux-image-lowlatency 4.4.0.214.221
linux-image-virtual 4.4.0.214.221

Ubuntu 14.04 ESM:
linux-image-4.4.0-1096-aws 4.4.0-1096.101
linux-image-4.4.0-214-generic 4.4.0-214.246~14.04.1
linux-image-4.4.0-214-lowlatency 4.4.0-214.246~14.04.1
linux-image-aws 4.4.0.1096.94
linux-image-generic-lts-xenial 4.4.0.214.187
linux-image-lowlatency-lts-xenial 4.4.0.214.187
linux-image-virtual-lts-xenial 4.4.0.214.187

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

ATTENTION: Due to an unavoidable ABI change the kernel updates have
been given a new version number, which requires you to recompile and
reinstall all third party kernel modules you might have installed.
Unless you manually uninstalled the standard kernel metapackages
(e.g. linux-generic, linux-generic-lts-RELEASE, linux-virtual,
linux-powerpc), a standard system upgrade will automatically perform
this as well.

References:
  https://ubuntu.com/security/notices/USN-5062-1
CVE-2021-3653