[USN-7874-3] Linux kernel (IoT) vulnerabilities

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==========================================================================
Ubuntu Security Notice USN-7874-3
December 04, 2025

linux-iot vulnerabilities
==========================================================================

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

- Ubuntu 20.04 LTS

Summary:

Several security issues were fixed in the Linux kernel.

Software Description:
- linux-iot: Linux kernel for IoT platforms

Details:

Jean-Claude Graf, Sandro Rüegge, Ali Hajiabadi, and Kaveh Razavi discovered
that the Linux kernel contained insufficient branch predictor isolation
between a guest and a userspace hypervisor for certain processors. This
flaw is known as VMSCAPE. An attacker in a guest VM could possibly use this
to expose sensitive information from the host OS. (CVE-2025-40300)

Several security issues were discovered in the Linux kernel.
An attacker could possibly use these to compromise the system.
This update corrects flaws in the following subsystems:
- HSI subsystem;
- I3C subsystem;
- SMB network file system;
- Padata parallel execution mechanism;
- Timer subsystem;
- Networking core;
(CVE-2023-52854, CVE-2024-35867, CVE-2024-50061, CVE-2024-56664,
CVE-2025-21727, CVE-2025-37838, CVE-2025-38352)

Update instructions:

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

Ubuntu 20.04 LTS
linux-image-5.4.0-1056-iot 5.4.0-1056.59
Available with Ubuntu Pro

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-7874-3
https://ubuntu.com/security/notices/USN-7874-2
https://ubuntu.com/security/notices/USN-7874-1
CVE-2023-52854, CVE-2024-35867, CVE-2024-50061, CVE-2024-56664,
CVE-2025-21727, CVE-2025-37838, CVE-2025-38352, CVE-2025-40300