A Linux kernel security update has been released for Ubuntu Linux 14.04 ESM and 16.04 LTS to address several security issues in the linux and linux-lts-xenial kernels.

USN-4708-1: Linux kernel vulnerabilities

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Ubuntu Security Notice USN-4708-1
January 28, 2021

linux, linux-lts-xenial vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 16.04 LTS
- Ubuntu 14.04 ESM

Summary:

Several security issues were fixed in the Linux kernel.

Software Description:
- linux: Linux kernel
- linux-lts-xenial: Linux hardware enablement kernel from Xenial for Trusty

Details:

Wen Xu discovered that the XFS filesystem implementation in the Linux
kernel did not properly track inode validations. An attacker could use this
to construct a malicious XFS image that, when mounted, could cause a denial
of service (system crash). (CVE-2018-13093)

It was discovered that the btrfs file system implementation in the Linux
kernel did not properly validate file system metadata in some situations.
An attacker could use this to construct a malicious btrfs image that, when
mounted, could cause a denial of service (system crash). (CVE-2019-19813,
CVE-2019-19816)

Bodong Zhao discovered a use-after-free in the Sun keyboard driver
implementation in the Linux kernel. A local attacker could use this to
cause a denial of service or possibly execute arbitrary code.
(CVE-2020-25669)

Daniel Axtens discovered that PowerPC RTAS implementation in the Linux
kernel did not properly restrict memory accesses in some situations. A
privileged local attacker could use this to arbitrarily modify kernel
memory, potentially bypassing kernel lockdown restrictions.
(CVE-2020-27777)

Update instructions:

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

Ubuntu 16.04 LTS:
linux-image-4.4.0-201-generic 4.4.0-201.233
linux-image-4.4.0-201-generic-lpae 4.4.0-201.233
linux-image-4.4.0-201-lowlatency 4.4.0-201.233
linux-image-4.4.0-201-powerpc-e500mc 4.4.0-201.233
linux-image-4.4.0-201-powerpc-smp 4.4.0-201.233
linux-image-4.4.0-201-powerpc64-emb 4.4.0-201.233
linux-image-4.4.0-201-powerpc64-smp 4.4.0-201.233
linux-image-generic 4.4.0.201.207
linux-image-generic-lpae 4.4.0.201.207
linux-image-lowlatency 4.4.0.201.207
linux-image-powerpc-e500mc 4.4.0.201.207
linux-image-powerpc-smp 4.4.0.201.207
linux-image-powerpc64-emb 4.4.0.201.207
linux-image-powerpc64-smp 4.4.0.201.207
linux-image-virtual 4.4.0.201.207

Ubuntu 14.04 ESM:
linux-image-4.4.0-201-generic 4.4.0-201.233~14.04.1
linux-image-4.4.0-201-generic-lpae 4.4.0-201.233~14.04.1
linux-image-4.4.0-201-lowlatency 4.4.0-201.233~14.04.1
linux-image-4.4.0-201-powerpc-e500mc 4.4.0-201.233~14.04.1
linux-image-4.4.0-201-powerpc-smp 4.4.0-201.233~14.04.1
linux-image-4.4.0-201-powerpc64-emb 4.4.0-201.233~14.04.1
linux-image-4.4.0-201-powerpc64-smp 4.4.0-201.233~14.04.1
linux-image-generic-lpae-lts-xenial 4.4.0.201.176
linux-image-generic-lts-xenial 4.4.0.201.176
linux-image-lowlatency-lts-xenial 4.4.0.201.176
linux-image-powerpc-e500mc-lts-xenial 4.4.0.201.176
linux-image-powerpc-smp-lts-xenial 4.4.0.201.176
linux-image-powerpc64-emb-lts-xenial 4.4.0.201.176
linux-image-powerpc64-smp-lts-xenial 4.4.0.201.176
linux-image-virtual-lts-xenial 4.4.0.201.176

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://usn.ubuntu.com/4708-1
CVE-2018-13093, CVE-2019-19813, CVE-2019-19816, CVE-2020-25669,
CVE-2020-27777

Package Information:
  https://launchpad.net/ubuntu/+source/linux/4.4.0-201.233