[USN-7861-2] Linux kernel (Real-time) vulnerabilities

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==========================================================================
Ubuntu Security Notice USN-7861-2
November 07, 2025

linux-realtime, linux-realtime-6.8 vulnerabilities
==========================================================================

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

- Ubuntu 24.04 LTS
- Ubuntu 22.04 LTS

Summary:

Several security issues were fixed in the Linux kernel.

Software Description:
- linux-realtime: Linux kernel for Real-time systems
- linux-realtime-6.8: Linux kernel for Real-time systems

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.

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;
- Bluetooth subsystem;
- Timer subsystem;
(CVE-2025-37838, CVE-2025-38118, CVE-2025-38352)

Update instructions:

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

Ubuntu 24.04 LTS
linux-image-6.8.1-1037-realtime 6.8.1-1037.38
Available with Ubuntu Pro
linux-image-realtime 6.8.1-1037.38
Available with Ubuntu Pro
linux-image-realtime-6.8.1 6.8.1-1037.38
Available with Ubuntu Pro

Ubuntu 22.04 LTS
linux-image-6.8.1-1037-realtime 6.8.1-1037.38~22.04.1
Available with Ubuntu Pro
linux-image-realtime-6.8.1 6.8.1-1037.38~22.04.1
Available with Ubuntu Pro
linux-image-realtime-hwe-22.04 6.8.1-1037.38~22.04.1
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-7861-2
https://ubuntu.com/security/notices/USN-7861-1
CVE-2025-37838, CVE-2025-38118, CVE-2025-38352, CVE-2025-40300

Package Information:
https://launchpad.net/ubuntu/+source/linux-realtime/6.8.1-1037.38

https://launchpad.net/ubuntu/+source/linux-realtime-6.8/6.8.1-1037.38~22.04.1