A Linux kernel security update has been released for Ubuntu Linux 16.04 LTS and 18.04 LTS.

[USN-6396-1] Linux kernel vulnerabilities

==========================================================================
Ubuntu Security Notice USN-6396-1
September 26, 2023

linux, linux-aws, linux-aws-hwe, linux-azure, linux-azure-4.15, linux-gcp,
linux-gcp-4.15, linux-hwe, linux-oracle vulnerabilities
==========================================================================

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

- Ubuntu 18.04 LTS (Available with Ubuntu Pro)
- Ubuntu 16.04 LTS (Available with Ubuntu Pro)

Summary:

Several security issues were fixed in the Linux kernel.

Software Description:
- linux: Linux kernel
- linux-aws: Linux kernel for Amazon Web Services (AWS) systems
- linux-azure-4.15: Linux kernel for Microsoft Azure Cloud systems
- linux-gcp-4.15: Linux kernel for Google Cloud Platform (GCP) systems
- linux-aws-hwe: Linux kernel for Amazon Web Services (AWS-HWE) systems
- linux-azure: Linux kernel for Microsoft Azure Cloud systems
- linux-gcp: Linux kernel for Google Cloud Platform (GCP) systems
- linux-hwe: Linux hardware enablement (HWE) kernel
- linux-oracle: Linux kernel for Oracle Cloud systems

Details:

It was discovered that some AMD x86-64 processors with SMT enabled could
speculatively execute instructions using a return address from a sibling
thread. A local attacker could possibly use this to expose sensitive
information. (CVE-2022-27672)

Daniel Moghimi discovered that some Intel(R) Processors did not properly
clear microarchitectural state after speculative execution of various
instructions. A local unprivileged user could use this to obtain to
sensitive information. (CVE-2022-40982)

Yang Lan discovered that the GFS2 file system implementation in the Linux
kernel could attempt to dereference a null pointer in some situations. An
attacker could use this to construct a malicious GFS2 image that, when
mounted and operated on, could cause a denial of service (system crash).
(CVE-2023-3212)

It was discovered that the NFC implementation in the Linux kernel contained
a use-after-free vulnerability when performing peer-to-peer communication
in certain conditions. A privileged attacker could use this to cause a
denial of service (system crash) or possibly expose sensitive information
(kernel memory). (CVE-2023-3863)

It was discovered that the bluetooth subsystem in the Linux kernel did not
properly handle L2CAP socket release, leading to a use-after-free
vulnerability. A local attacker could use this to cause a denial of service
(system crash) or possibly execute arbitrary code. (CVE-2023-40283)

It was discovered that some network classifier implementations in the Linux
kernel contained use-after-free vulnerabilities. A local attacker could use
this to cause a denial of service (system crash) or possibly execute
arbitrary code. (CVE-2023-4128)

Update instructions:

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

Ubuntu 18.04 LTS (Available with Ubuntu Pro):
linux-image-4.15.0-1155-gcp 4.15.0-1155.172
linux-image-4.15.0-1161-aws 4.15.0-1161.174
linux-image-4.15.0-1170-azure 4.15.0-1170.185
linux-image-4.15.0-218-generic 4.15.0-218.229
linux-image-4.15.0-218-lowlatency 4.15.0-218.229
linux-image-aws-lts-18.04 4.15.0.1161.159
linux-image-azure-lts-18.04 4.15.0.1170.138
linux-image-gcp-lts-18.04 4.15.0.1155.169
linux-image-generic 4.15.0.218.202
linux-image-lowlatency 4.15.0.218.202
linux-image-virtual 4.15.0.218.202

Ubuntu 16.04 LTS (Available with Ubuntu Pro):
linux-image-4.15.0-1124-oracle 4.15.0-1124.135~16.04.1
linux-image-4.15.0-1155-gcp 4.15.0-1155.172~16.04.1
linux-image-4.15.0-1161-aws 4.15.0-1161.174~16.04.1
linux-image-4.15.0-1170-azure 4.15.0-1170.185~16.04.1
linux-image-4.15.0-218-generic 4.15.0-218.229~16.04.1
linux-image-4.15.0-218-lowlatency 4.15.0-218.229~16.04.1
linux-image-aws-hwe 4.15.0.1161.144
linux-image-azure 4.15.0.1170.154
linux-image-gcp 4.15.0.1155.145
linux-image-generic-hwe-16.04 4.15.0.218.2
linux-image-gke 4.15.0.1155.145
linux-image-lowlatency-hwe-16.04 4.15.0.218.2
linux-image-oem 4.15.0.218.2
linux-image-oracle 4.15.0.1124.105
linux-image-virtual-hwe-16.04 4.15.0.218.2

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-6396-1
CVE-2022-27672, CVE-2022-40982, CVE-2023-3212, CVE-2023-3863,
CVE-2023-40283, CVE-2023-4128